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Wind activity is a powerful force that shapes the landscapes of deserts, coastal areas, and regions adjacent to ice sheets, and it has significant implications for human settlement. In southern Greenland, it has been proposed that the increased wind and soil erosion observed around Norse settlements (~985–1450 CE) were caused by overgrazing by animals, which ultimately contributed to the decline of the Norse culture. Alternatively, some studies have linked the observed intensification of aeolian activity to changes in large‐scale atmospheric circulation patterns in the North Atlantic. However, the timing and impact of this increased aeolian activity in southern Greenland remain uncertain due to a lack of well‐dated records. In this study, we use a lake record and optically stimulated luminescence (OSL) dating of adjacent dunes to reconstruct the Holocene history of aeolian activity at Igaliku Kujalleq (Søndre Igaliku) in southern Greenland. Our findings indicate two periods of intensified aeolian activity over the past 10 000 years: from ~500 to 1200 CE and ~1450 CE. Importantly, the peak aeolian activity observed in the Igaliku Kujalleq records was unrelated to Norse activities and their decline. Instead, we suggest that changes in the North Atlantic atmospheric circulation pattern combined with Neoglacial glacier advances led to increased katabatic wind activity and triggered increased aeolian activity from large outwash plains. [ABSTRACT FROM AUTHOR]

This study projects the changes in tropical cyclone (TC) landfalls in the western North Pacific under shared socioeconomic pathway (SSPs) scenarios during the TC peak season by using low‐resolution global climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). Projections are based on the relationship between mid‐ and lower‐level atmospheric circulation and TC landfall frequency during the historical period from 1985 to 2014 and the future climate period from 2015 to 2100. The landfall areas for TCs are divided into northern East Asia (NEA), middle East Asia (MEA) and southern East Asia (SEA); the TC peak seasons are July–September for NEA and MEA, and July–November for SEA. To evaluate reproducibility, both ensemble and individual model outputs for mid‐ and lower‐level atmospheric circulations associated with TC landfall in each East Asian subregion are compared to the reanalysis. An ensemble of seven models with stable results for all three regions is more reasonable in simulating atmospheric circulation patterns than an ensemble of all CMIP6 models. The findings suggest that TC landfall is projected to increase by about 12% and 32% in NEA and MEA, respectively, in the late 21st century under the SSP5‐8.5 scenario compared to the historical period, while decreasing by 13% in SEA. These changes are consistent under both warming scenarios, and are more pronounced in the SSP5‐8.5 scenario compared to SSP1‐2.6, particularly in the later period of this century. An analysis of future atmospheric circulations suggests that global warming will weaken the western North Pacific subtropical high and cause its boundary to retreat eastward. This will lead to changes in the steering flow, which is closely related to TC tracks, resulting in TC landfalls to increase or decrease depending on the East Asian subregion. [ABSTRACT FROM AUTHOR]

Arctic Oscillation (AO) is the dominant mode of atmospheric circulation in the extratropical Northern Hemisphere regions. The spatial pattern of the AO Arctic center affects the extent of polar cold air outbreaks southward. However, the underlying nature and causes of its interdecadal variation remain unclear. Utilizing ERA5 reanalysis data, this study identifies two distinct spatial patterns of the wintertime AO Arctic center through the K‐means clustering method, which alternate over different decade periods. The Double‐trough pattern generates a tripolar temperature pattern of "cold Arctic‐warm Eurasia‐cold Tibetan Plateau" through a Rossby wave train during 1960–1997/2013–2024. While the Single‐trough pattern leads to a dipolar temperature pattern in 1998–2012. Furthermore, interdecadal variations in North Atlantic sea surface temperature meridional gradient act as an influencing factor in shaping the spatial pattern of the AO Arctic center. This research aids the understanding and prediction of climate anomalies using AO signals within various decadal contexts. Plain Language Summary: Arctic Oscillation (AO) is a key extratropical atmospheric variability mode in the Northern Hemisphere, significantly influencing weather and climate anomalies in the mid‐latitudes. The shape of AO's trough in the Arctic center governs the southward advancement of Arctic cold air. Using the K‐means clustering method, the spatial patterns of the wintertime AO Arctic center are primarily divided into two distinct categories, which alternate across different decades. Specifically, from 1960 to 1997 and 2013 to 2024, the AO Arctic center exhibits dual troughs over the Ural Mountains and North America, resulting in a distribution of "cold Arctic‐warm Eurasia‐cold Tibetan Plateau." However, during the period from 1998 to 2012, only the North American trough is present, and its temperature connection with Eurasia weakens. Notably, interdecadal variations in the AO Arctic center are affected by North Atlantic sea surface temperature meridional gradient. This study enhances our understanding of the physical significance of AO and assists us in better utilizing it to predict winter weather and climate anomalies. Key Points: The AO Arctic center shows two spatial patterns alternating between Double‐ and Single‐trough configurations on an interdecadal timescaleThe two spatial patterns of the AO Arctic center are modulated by the interdecadal variations of North Atlantic SST meridional gradientThe Double‐trough pattern of the AO Arctic center can cause a unique tripolar pattern of "cold Arctic‐warm Eurasia‐cold Tibetan Plateau" [ABSTRACT FROM AUTHOR]

Understanding sub‐daily precipitation extremes (SPEs) can provide scientific insights for taking effective measures to mitigate climate risks. Leveraging gauge observations at hourly precipitation in 2,312 meteorological stations and extreme sub‐daily precipitation indices (ESPIs), we investigate the changes of SPEs in flooding season of 1971–2022 in China. On country scale, the occurrences and intensity of SPEs have significantly increased and even accelerated since the 21st century, suggesting increases in 2010s by 15%–38% compared with that in 1970s. The SPE risks for 20‐year and 50‐year return‐period increased by 2–4 and 8–20 times in 2001–2022 compared with that in 1971–2000, respectively. Over 80% stations are found to have positive trends in all ESPIs. On regional scale, seven sub‐regions experienced significant increases in ESPIs with larger magnitudes in the East China. The enlarged 500‐hPa geopotential height, 700‐hPa pseudoequivalent potential temperature, 700‐hPa specific humidity, saturated vapor pressure and urbanization ratio may be bonded to more SPEs. Plain Language Summary: Short‐term precipitation extremes have serious impacts on human safety, agriculture, energy, and infrastructure. It is very urgent to understand their variations and underlying mechanisms for policy‐makers to take effective approaches to mitigate extreme precipitation‐related risks. Here, we investigate the spatio‐temporal changes of sub‐daily precipitation extremes in the flooding season of 1971–2022 in China. We examine six metrics of extreme sub‐daily precipitation based on hourly observation data. We find that the occurrences and intensity of SPEs have significantly increased during the recent 52 years with acceleration since the 21st century on both country and regional level. The once‐in‐20‐year and once‐in‐50‐year events in 2001–2022 increased by 2–4 and 8–20 times compared with that in 1971–2000, respectively. The larger upward magnitudes of ESPIs are mainly located in the East China. In the era of rapid global warming, thermodynamic effects of abnormal atmospheric circulation and rapid urbanization possibly facilitate the occurrences of more SPEs in China. Key Points: Sub‐daily precipitation extremes have substantially increased over China during 1971–2022, even accelerating since the 21st centuryMost of China exhibits consistent upward trends in all extreme sub‐daily precipitation indices with lager magnitudes in the East ChinaThermodynamic effects of abnormal atmospheric circulation and urbanization are possibly boned to increased sub‐daily precipitation extremes [ABSTRACT FROM AUTHOR]

The coast of Terra Nova Bay (TNB) is known as one of the intense katabatic wind confluence zones in Antarctica. Strong westerly winds with topography‐specific foehn effects (foehn‐like winds, FLWs) could have influenced surface temperatures in this area downwind of the Transantarctic Mountains, yet their impact remains unstudied. Jang Bogo Station (JBS) in TNB has weak winds year‐round, with occasional strong winds causing significant winter temperature increases. This study aims to investigate the FLWs and their recent variability in occurrence at JBS in terms of surface temperature variability. During the strong wind events, the surface warms due to foehn effects such as adiabatic heating and vertical mixing. FLWs occur approximately 16% (10%) of the time in winter (annually). FLWs are caused by cyclones in the eastern Ross Sea. Meteorological records for 2015–2022 revealed an increased FLW frequency, particularly in winter, which has increased temperatures in recent years. Plain Language Summary: Foehn is mainly related to winds ascending along high mountains, and the resulting descending winds make the air warm and dry on the mountain's leeward side. They significantly contribute to rising surface temperature and melting ice shelf in Antarctica. Foehn‐like winds (FLWs), different from typical foehn but with the same effect, were speculated to occur on the coasts of Terra Nova Bay (TNB), Ross Sea, which are known to have intense katabatic winds (strong and cold air blowing along a slope inland to the coast) year‐round because most coastal areas are located downwind of the Transantarctic Mountains. This study investigated whether strong inland winds are foehn‐like and related to the recent temperature increase at Jang Bogo Station in TNB. We found that the downward strong westerly winds from inland are foehn‐like, and their increase in frequency has increased the surface temperature at Jang Bogo Station over the last 8 years. Large‐scale cyclones in the eastern Ross Sea are responsible for FLWs. The change in FLW frequency may imply atmospheric circulation changes over the Ross Sea. Key Points: The study showed that the foehn effect is significant when strong inland winds blow from west, particularly in winterThe recent rise in winter temperatures is related to an increase in the frequency of foehn‐like wind aboveSynoptic scale cyclones centered in the eastern Ross Sea cause foehn‐like winds at Jang Bogo Station [ABSTRACT FROM AUTHOR]

A fundamental characteristic of extreme precipitation events (EPEs) is their horizontal scale. This horizontal scale can influence the intensity of an EPE through its effect on the timescale of an EPE as well as its effect on the strength of convective feedbacks. Thus, to have confidence in future projections of extreme precipitation, the horizontal scales of EPEs in global climate models (GCMs) should be evaluated. Analyzing daily output from 27 models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6), including 13 models participating in the High Resolution Model Intercomparison Project (HighResMIP), we computed the horizontal scales of EPEs and extreme ascent for annual maximum EPEs during 1981–2000. We found that the horizontal scales of both EPEs and the associated ascending motion are resolution‐dependent: for a factor of seven increase in horizontal resolution, the horizontal scale decreases by a factor of approximately two to five, with higher sensitivity in the tropics than in the midlatitudes. Further analysis in the southern hemisphere midlatitudes reveals that this resolution dependence results from precipitation during the simulated EPEs that is almost entirely resolved rather than parameterized. However, the EPEs are not simply grid box storms, and analysis of the horizontal scales of geopotential anomalies suggests that the planetary‐scale dynamics in GCMs is not resolution‐dependent. Thus, the dominance of resolved precipitation during EPEs is more likely due to convection on the model grid or formation of strong, poorly resolved fronts, and additional work is needed to explore these possibilities and find a remedy for this resolution dependence. Plain Language Summary: Extreme precipitation is of great human interest because of the potentially severe flooding that it can cause. We are reliant on global climate models (GCMs) to project future changes in extreme precipitation, so there is a need to assess the realism of extreme precipitation in GCMs. One fundamental characteristic of an extreme precipitation event (EPE) is its horizontal size or "scale." In this study, we analyze a large archive of output from simulations using state‐of‐the‐art GCMs and compute the horizontal scale of EPEs during 1981–2000. We found that the horizontal scale depends on the spacing between grid points in the model. These grid points are like pixels in a digital photo, and the smaller the distance between grid points, the higher the model resolution. The fact that the EPE horizontal scale in GCMs is resolution‐dependent is concerning because the horizontal scale should be dictated by realistic physical processes rather than artificial aspects of the model configuration. While we have provided some initial insights into the reasons for this resolution dependence, additional work is needed to develop more complete explanations and improve models. Key Points: The simulated horizontal scale of the annual maximum of daily precipitation anomalies is sensitive to a model's horizontal resolutionThis extreme precipitation horizontal scale is determined almost entirely by resolved, not parameterized, precipitationThe simulated horizontal scale of geopotential disturbances during these extreme precipitation events is not resolution dependent [ABSTRACT FROM AUTHOR]

In this study, a record‐breaking surface gust wind event of over 45 m s−1, which occurred in the coastal region of East China during the early evening hours of 30 April 2021, is examined. The dynamical characteristics of this event is explored by using a high‐resolution mesonet comprised of eight radar wind profilers (RWPs), surface observations, radar and satellite data. Observational analyses show the development of several cloud clusters ahead of the axis of a midlevel trough with pronounced baroclinicity, and the subsequent organization into a comma‐shaped squall system with a leading convective line over land and a trailing stratiform region moved offshore. The latter is embedded by a mesovortex with intense northerly rear inflows descending to the surface, accounting for the generation of the gusty winds. Results indicate the different roles of multi‐scale processes in accelerating the surface winds to extreme intensity. Specifically, the large‐scale baroclinic trough provides intense background rear inflows that are enhanced by the formation of the mesovortex, while moist downdrafts in the rear inflows account for the downward transport of horizontal momentum, leading to the generation of intense cold outflows and gusty winds close to the leading convective line. Despite the lack of sufficient observations for quantitative analysis, this study provides a qualitative analysis that offers valuable insights into the dynamics of extreme gusty winds. Moreover, the above results underscore the value of RWP mesonet observations in enhancing our understanding of extreme wind events and in improving the nowcasting and prediction efforts in the future. Plain Language Summary: Predicting extreme surface wind events is challenging, especially under a warming climate, which desperately needs high‐resolution three‐dimensional atmospheric observations. This study focuses on a record‐breaking gust‐wind event in East China, using data from a network of radar wind profilers (RWPs). These instruments allow us to analyze how atmospheric dynamics evolves during the event. We found that the extreme wind is determined by multiscale flows: an intense background flow that is enhanced by a mesovortex, and the downward transport of higher horizontal momentum in convective downdrafts behind the gust front. This research underscores the complex interactions that lead to extreme winds and highlights the value of RWP networks in enhancing our ability to monitor and predict such events. Key Points: A mesonet consisting of eight radar wind profilers captures the vertical structures and evolution of an extreme gust‐wind eventDownward transport of intense mid‐tropospheric horizontal momentum is key to the extreme wind eventThe extreme wind event is enhanced by descending rear inflows associated with a mesovortex [ABSTRACT FROM AUTHOR]

ABSTRACT The Indo‐Pacific warm pool (IPWP), enclosed by a 28°C isotherm, is vital in controlling atmospheric circulations affecting monsoonal flow. The warming trend of sea surface temperatures (SSTs) over the IPWP has expanded the IPWP region. This study examines the impact of the IPWP warming on the Indian summer monsoon rainfall (ISMR) patterns using ERA5 reanalysis and India Meteorological Department rainfall records based on station data from 1959 to 2021. Analyses based on correlation, regression and composite anomalies show the complex relationship between recent decades of IPWP expansion/warming and monsoon circulation. However, the effects of regional IPWP SST warming changes on the ISMR pattern remain unexplored. Here, we explore the changes in the monsoonal circulation owing to the warming and expansion of IPWP, by comparing two equal periods (1959–1989 and 1990–2021). The responses of monsoons to IPWP warming in these two periods revealed some interesting facts, but the complexity remained. Further, we examined the composite impacts of IPWP SST warming in three categories, that is, very cool, usual and extremely warm, on the dynamics of monsoon circulations. The very cool IPWP is associated with the dry monsoon, while the extremely warm IPWP produces copious rainfall over southern India and dryness over eastern north India. The study confirms the non‐linear relationship between IPWP warming and ISMR, which has been investigated in detail. [ABSTRACT FROM AUTHOR]

Synoptic climatology, which connects atmospheric circulation with regional environmental conditions, is pivotal to understanding climate dynamics. While regional climate models (RCMs) can reproduce key mesoscale precipitation patterns, biases related to synoptic circulation from the driving model, typically global climate models (GCMs), often remain unaddressed. This study examines the influence of correcting systematic bias in RCM boundaries on the representation of Australian synoptic systems. We utilize a structural self‐organizing map to evaluate the frequency, persistence, and transitions of daily synoptic systems. Our findings reveal that an RCM with multivariate bias‐corrected boundaries improves the representation of synoptic systems compared to the driving GCM, or an RCM with uncorrected or simply bias‐corrected boundaries, particularly in reference to the frequency of systems identified. This demonstrates that appropriately correcting RCM boundary conditions helps correct many of the circulation errors inherited from the driving GCM but not all. Plain Language Summary: Global climate models (GCMs) have limitations in accurately simulating precipitation characteristics at finer scales. Regional climate models (RCMs), driven by GCM data, are employed to overcome these limitations. However, GCM biases in regional circulations are inherited by the RCM, leading to errors in the simulated weather. This study investigates the effects of multivariate bias correction of RCM boundary conditions on the model's ability to simulate daily synoptic systems. Results indicate that RCMs with corrected boundaries better represent weather systems, overcoming some of the circulation errors in the GCM. Key Points: Regional climate models (RCMs) with uncorrected and simple bias‐corrected boundaries show large errors when simulating climatological frequency of synoptic systemsAn RCM with multivariate bias‐corrected boundaries demonstrates enhanced accuracy in the simulation of synoptic systemsThese findings demonstrate that correcting RCM boundaries improves the RCM representation of weather systems as well as the climate [ABSTRACT FROM AUTHOR]

Despite routine detection of coseismic acoustic‐gravity waves (AGWs) in Global Navigation Satellite System (GNSS) total electron content (TEC) observations, models of the earthquake‐atmosphere‐ionosphere dynamics, essential for validating data‐driven studies, remain limited. We present the results of three‐dimensional numerical simulations encompassing the entire coupling from Earth's interior to the ionosphere during the Mw ${M}_{w}$ 7.8 2016 Kaikoura earthquake. Incorporating the impact of data/model uncertainties in estimating the ionospheric state, the results show a good agreement between observed and simulated slant TEC (sTEC) signals, assessed through a set of metrics. The signals exhibit intricate waveforms, resulting from the integrated nature of TEC and phase cancellation effects, emphasizing the significance of direct signal comparisons along realistic line‐of‐sight paths. By comparing simulation results initialized with kinematic and dynamic source models, the study demonstrates the quantifiable sensitivity of sTEC to AGW source specifications, pointing to their utility in the analysis of coupled dynamics. Plain Language Summary: Earthquakes launch acoustic‐gravity waves (AGWs) into the atmosphere, spanning periods from seconds to minutes, that can reach the ionosphere at ∼ ${\sim} $100–400 km altitude. The majority of AGW detections in the ionosphere are performed with the use of GNSS signals collected with ground‐based receivers that nowadays comprehensively cover seismically active regions. However, the modeling of earthquake‐atmosphere‐ionosphere processes together, essential for validating and supporting data‐driven studies, remains rare. We present the outcomes of three‐dimensional numerical modeling of interconnected processes, spanning from Earth's interior to the ionosphere. We conducted a case study focused on the 2016 Mw ${M}_{w}$ 7.8 earthquake in New Zealand, renowned for its complexity and comprehensive observations of coseismic AGWs recorded with GNSS signals. Our results demonstrate a high level of accuracy of simulated GNSS signals, also revealing the high sensitivity to the chosen earthquake model and the complexity of resulting ionospheric signals, highlighting the necessity of attributing realistic geometries of GNSS TEC observations. The findings highlight the potential for using GNSS signals to investigate coseismic AGWs to infer characteristics of earthquakes. Key Points: Acoustic‐gravity wave‐driven slant total electron content (sTEC) signals are analyzed in terms of amplitude, waveform, and onset timeIntricate sTEC signal waveforms result from ionospheric fluctuations measured along lines‐of‐sight between satellites and receiversHigh sensitivity of sTEC signals to acoustic‐gravity wave source specification provides additional basis for earthquake characterization [ABSTRACT FROM AUTHOR]

Compound hazards involving tropical cyclones and extreme heat ("TC‐heat") have rarely been examined in prior research. Peripheral subsidence associated with cyclones can warm an area to varying degrees, depending on the cyclone's strength and position. Meanwhile, the peripheral airflow also overwhelmed the land‐sea breeze circulation system in coastal cities and favored downwind urbanized heat advection on the Southern China coastline. Here, we systematically applied ERA5 global reanalysis data, local surface‐level observations, MODIS‐based land‐cover data and HYSPLIT backward trajectories to evaluate how the position of distant TCs may divert the monsoon system and foster the surface heat advection from upwind urban agglomerate amplifying air temperature in downwind coastline. The analysis suggests when a distant TC is situated in a favorable area (the vicinity of Taiwan and Luzon Strait) at roughly 500–1,250 km to the east of Hong Kong, it forms a unique meteorological condition which allows the surface heat transport from the Greater Bay Area to Hong Kong, reflecting that regional build‐up of heat could be an important mechanism for producing local heat extremes. Plain Language Summary: Rapid urbanization and global climate change bring us new hazards through compound extreme weather events in urban society. Tropical cyclones (TC) are known to bring violent wind and heavy rain upon arrival, while in distant they can also send very hot weather conditions (called TC‐heat events) to regions under its subsidence airflow. This study shows the combined effect of heat from upwind urban areas in coincidence with the TC‐induced subsidence could bring even higher temperatures to the downstream cities like Hong Kong. Comprehensive analysis with global climate data, local weather observations, and backward simulation models were used to further understand how the location of TC may adverse the wind circulation patterns in inland areas and contribute to a larger extreme heat threat to the coastal cities. This can facilitate the early forecast and warning for the potential occurrence of such TC‐heat compound hazard, potentially benefitting public preparedness and response in combating extreme heat and cyclone influences. Key Points: High temperature events occur when distant Tropical Cyclone (DistTC) located at 500–1,250 km from Hong KongSurface heat can be built‐up in inland China cities, transport to Hong Kong as downwind footprint and contribute to the temperature enhancementProbability of high temperature events with DistTC is 15% higher than the normal summer days in Hong Kong [ABSTRACT FROM AUTHOR]

The theory of radiative transfer in the atmosphere is crucial in the study of climate, because radiative exchanges are at the origin of the atmospheric dynamics. It is therefore important to evaluate this phenomenon in order to be able to take effective measures to tackle climate change. The objective of this work is to evaluate the capability of the RegCM5 climate model to reproduce radiative transfer over Central Africa. The analysis is carried out over a 10‐year period, from January 2002 to December 2011 preceded by 1 year as spin‐up. RegCM5 model were evaluated using the ERA5 dataset for the radiative transfer parameters (the shortwave radiation [SWR], longwave radiation [LWR], cloud cover [CLT], surface albedo [ALB] and surface temperature), as well as CHIRPS dataset for precipitation. Three subregions were identified for more specific analysis of the model, namely the Sahel, Congo basin and Cameroon highlands. Two radiative schemes were used: the radiative scheme of the community climate model (CCM) and Rapid Radiative Transfer Model (RRTM). The assessment of radiative transfer parameters was carried out by examining their seasonal variability and annual cycles using data from two RegCM5 experiments, RegCM5‐CCM3 and RegCM5‐RRTM. Before this assessment, a sensibility analysis to convective schemes carried out with the default RegCM5 radiative scheme (CCM3) shows that Grell scheme with Arakawa and Shulber closure is the best scheme to represent key radiation parameters (LWR and SWR). This convective scheme is therefore used for assessing the two Radiative transfer schemes. Results show that both RegCM5 experiments simulate relatively well the variables linked to radiative transfer for the four seasons of the year. However, RegCM5 with RRTM as radiative scheme depicts better performance over all subregions and seasons, suggesting that the choice of this scheme does not depend on land cover, topography and rainfall regimes in a complex region such as Central Africa. [ABSTRACT FROM AUTHOR]

In recent decades, India has witnessed an increase in the intensity, frequency, and spread of extreme weather events. The widespread increase in extreme precipitation over the Western Coast of India is a matter of great concern. The factors contributing to such devastating extreme precipitation remain unclear due to the variability present in meteorological and oceanic variables and associated large‐scale circulations. Using reanalysis and observed datasets, we attempted to identify a combination of dynamic, thermodynamic, and cloud microphysics processes contributing to the anomalous precipitation from August 1 to 10, 2019 against its climatology. Our key findings highlight the crucial role of warm sea surface temperatures (anomaly >1.4°C), outgoing longwave radiation (anomaly <−50 W·m−2), and atmospheric temperature (anomaly over the ocean is >1.6°C) in enhancing the moisture‐holding capacity of the atmosphere by almost 10%. This elevated moisture, propelled by intensified low‐level winds (anomalies exceeding 4 m·s−1), leads to a shift from ocean to land. Notably, we observe that vertical updrafts (anomalies >−0.4 m·s−1) contribute to increased atmospheric instability and moisture convergence. The presence of an ample amount of cloud hydrometeors, with anomalies surpassing 2.5 × 10−4 kg·kg−1, establishes conditions conducive to sustained intense precipitation. Our findings deepen our understanding of the complex relationships between ocean and atmospheric dynamics, and wind patterns, and emphasize their pivotal influence on regional weather patterns and land surface hydrology. [ABSTRACT FROM AUTHOR]

The current study investigates the modulation of the tropical cyclone (TC) frequency (TCF) over the Bay of Bengal (BoB) by the southern annular mode (SAM). The analysis reveals that the SAM–TCF relationship during October–November–December has undergone interdecadal changes from significant during 1971–1994 to insignificant during 1995–2021. This contrasting influence of the SAM on the TCF occurrence is also echoed in the large‐scale environmental variables conducive to forming tropical cyclones (TCs). Based on the possible mechanism, we found that the SAM can imprint tripole sea surface temperature (SST) patterns in the southern Indian Ocean via altering surface wind speed from 1971 to 1994. The SAM‐related tripole SST pattern induces the surface‐level anticyclone anomaly, which enhances the south easterlies towards the western equatorial Indian Ocean. Such intensified anomalous wind crosses the equator and diverts towards the east to form the cyclone anomaly in the BoB. Meanwhile, at 200 hPa, the anomalous anticyclone over western Australia induces divergent wind flows over the study region. Consequently, the ascending motion in BoB promotes the tropical cyclone generation. During 1995–2021, however, the SAM is associated with the dipole SST pattern in the southern Indian Ocean. Correspondingly, the SAM‐related dipole SST yields anomalous atmospheric circulations confined to the Southern Hemisphere and eventually fails to impact the formation of TCs in the northern Indian Ocean, where the study region is located. The findings of this research can be useful in advancing our knowledge of the interannual variability of TCs activity in the BoB based on the remote climate signal. [ABSTRACT FROM AUTHOR]

Observational evidence shows that Sahel summer precipitation has experienced a considerable increase since the 1980s, coinciding with significant diverging trends of increased sulfate emissions in Asia and decreased emissions in Europe (dipole pattern of aerosols between Asia and Europe). The decrease in European sulfate aerosols has substantial effects on the Sahel summer precipitation increase, but the corresponding effect of increased Asian sulfate is unknown. Multi‐model simulations in the Precipitation Driver and Response Model Intercomparison Project (PDRMIP) show, compared to decreased European aerosols, that increased Asian aerosols similarly enhance the Sahel summer precipitation but with different large‐scale atmospheric circulation changes. Further analysis of the Sixth Coupled Model Intercomparison Project (CMIP6) simulations under historical attribution and various emission scenarios reinforces the results about the climate impacts of anthropogenic aerosols and suggests that in future scenarios with strong international cooperation and rapid climate mitigations (SSP2‐45), the Sahel drought will be intensified likely due to the decline in Asian aerosol emissions. Our results suggest that Asian anthropogenic aerosols are likely a non‐negligible driver of the recent recovery in Sahel precipitation amounts. Plain Language Summary: Due to the widespread influences of Sahel summer rainfall on local people's livelihoods, sustainable resource management, ecosystem, and food security, its dynamic evolution and driving factors are a severe socio‐economic concern. Owing to urbanization and industrialization, anthropogenic aerosol emissions over Asia have rapidly increased since the 1980s, but the climate impact of Asian aerosol emissions on local precipitation is unknown. Using the multi‐model simulations in the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), we show that increased Asian and reduced European sulfate aerosol emissions both enhance Sahel summer precipitation through different large‐scale atmospheric circulation changes. Here, we highlight the long‐range impact of Asian anthropogenic air pollutants on the recent recovery of Sahel precipitation and propose the Sahel drought will be intensified likely due to the decline in Asian aerosol emissions in future scenarios with strong international cooperation and rapid climate mitigations. Key Points: Increased Asian and reduced European sulfate aerosol emissions both enhance Sahel summer precipitationAsian anthropogenic aerosols partly drive the recent recovery in Sahel precipitation amountsThe Sahel drought will be intensified likely due to the reductions in Asian aerosol emissions in SSP2‐45 [ABSTRACT FROM AUTHOR]

Detecting and quantifying the global teleconnections with flash droughts (FDs) and understanding their causal relationships is crucial to improve their predictability. This study employs causal effect networks (CENs) to explore the global predictability sources of subseasonal soil moisture FDs in three regions of the United States (US): upper Mississippi, South Atlantic Gulf (SAG), and upper and lower Colorado river basins. We analyzed the causal relationships of FD events with global 2‐m air temperature, sea surface temperature, water deficit (precipitation minus evaporation), and geopotential height at 500 hPa at the weekly timescale over the warm season (April to September) from 1982 to 2018. CENs revealed that the Indian Ocean Dipole, Pacific North Atlantic patterns, Bermuda high‐pressure system, and teleconnection patterns via Rossby wave train and jet streams strongly influence FDs in these regions. Moreover, a strong link from South America suggests that atmospheric circulation forcings could affect the SAG through the low‐level atmospheric flow, reducing inland moisture transport, and leading to a precipitation deficit. Machine learning utilizing the identified causal regions and factors can well predict major FD events up to 4 weeks in advance, providing useful insights for improved subseasonal forecasting and early warnings. Plain Language Summary: This study investigates the global factors affecting flash droughts (FDs) in the upper Mississippi, South Atlantic Gulf, and upper and lower Colorado river basins in the United States. Using causal effect networks, the research identifies key global influences, such as the Indian Ocean Dipole, Pacific North Atlantic patterns, and Bermuda high‐pressure system, which affect FDs through atmospheric circulation and jet streams. Findings show that these factors, along with local and remote climate processes, can predict FDs up to 4 weeks in advance. Machine learning models utilizing these climate variables effectively forecast FDs events. The study highlights the importance of large‐scale climate oscillations and teleconnections in predicting FDs, offering useful insights for improving early warnings and climate risk management. Key Points: Causal discovery framework identified local and remote regions over the globe causing U.S. Flash droughts (FDs)Machine learning with climate variables over the discovered regions can well predict U.S. FDs up to 4 weeks in advanceThe discovered regions are consistent with the known sources of predictability but also reveal potentially new sources of predictability [ABSTRACT FROM AUTHOR]

Increased resolution has enabled kilometer‐scale weather and climate models to partially resolve secondary circulations, including horizontal convective rolls (HCRs) and cold pool gust fronts. Although these circulations are ubiquitous in convective boundary layers over land, their impacts on the surface energy balance are largely unknown. Doppler lidar and surface observations were combined with DOE E3SM land model experiments, revealing increased surface winds (5 m/s) and heat fluxes (50 W/m2) in convergent branches of HCRs. Larger wind‐driven flux responses (up to 150 W/m2) were found along gust fronts. Surface energy balance shifts to accommodate wind‐driven fluxes, reducing ground heat conduction and longwave cooling. Our findings from the US Southern Great Plains are broadly relevant to modeling convective boundary layers. In particular, widely used subgrid wind gust parameterizations were found to be physically inconsistent with resolved secondary circulations and could worsen climate prediction biases at kilometer‐scales. Plain Language Summary: Earth's surface is heated by solar radiation, and this energy is transferred to the overlying air in the form of sensible and latent heat fluxes. Surface heat fluxes are generated by turbulent motions that are too small to be directly simulated in weather and climate models. Instead, models use mathematical functions, known as parameterizations, to predict surface fluxes from simulated winds and surface‐to‐air differences in moisture and temperature. Observed winds near Earth's surface are known to organize into patterns referred to as secondary circulations, creating frequently observed "cloud streets," and influencing the soaring patterns of birds. With increasing computational power, weather, and climate models have begun to resolve these circulations in winds simulated at kilometer scales. Although they are widely observed, this study provides new evidence that secondary circulations significantly alter surface heat fluxes and the energy balance of the land surface. It is also shown that current parameterizations of wind‐driven heat fluxes can be made more realistic to improve predictions in weather and climate models that are run at kilometer‐scale spatial resolutions. Key Points: Lidar and surface wind measurements provide evidence linking widely observed secondary circulations to surface wind gustsThe circulations alter the land surface energy balance and increase surface heat fluxes in convergent branches of circulation updraftsLand model parameterizations are inconsistent with resolved circulations, pointing to needed improvements at kilometer‐scale resolutions [ABSTRACT FROM AUTHOR]

The sub‐grid turbulent orographic form drag (STOFD) significantly affects the regional circulation and precipitation. This study explores the local and remote effects of the STOFD on the summer monsoon precipitation across Eastern China using the Regional Climate Model Version 4 adopting a STOFD scheme. Results indicate that the local and remote effects of the STOFD primarily influence the improvement of summer precipitation simulation in the Southeastern and Northern China, respectively. The local effects of the STOFD can lead to 37.1% and 10.7% reduction of the absolute error and the root mean square error (RMSE) of simulated summer precipitation in the Southeastern China with complex sub‐grid terrains. The remote effects of the STOFD within the Indochina Peninsula and Yunnan‐Guizhou Plateau result in the absolute error and RMSE of simulated summer precipitation in the Northern China with mild sub‐grid terrain decreased by 90.1% and 32.9%, respectively. Moreover, the remote effects of the STOFD within the Tianshan Mountains and Tibetan Plateau can clearly improve the simulated precipitation in both the Southeastern and Northern China. The disturbances generated by the local effects of the STOFD are more locally concentrated than those produced by the STOFD remote effects, leading to a more significant improvement of precipitation simulation in the Southeastern China. While the disturbances resulted from the remote effects of the STOFD affect the summer precipitation in both the Southeastern and Northern China obviously. This study highlights the significance of the remote effects of the STOFD in improving the summer precipitation simulation in Eastern China. Plain Language Summary: Due to resolution limitations, micro‐scale terrains are often ignored in climate simulations. While the collision between airflow and sub‐grid micro‐scale terrains produces turbulence, which results in sub‐grid turbulent orographic form drag (STOFD). A STOFD scheme has been applied in the Regional Climate Model and proved its ability to improve the summer precipitation simulation in Eastern China. However, the specific source of the improvements remains unclear. This study explores the local and remote effects of the STOFD on precipitation simulation and reveals possible mechanisms. Results show that the remote effects of the STOFD greatly improve the precipitation simulation in the Northern China with mild sub‐grid terrains by inducing substantial disruptions in atmospheric circulation and related factors. Whereas both the local and remote effects of the STOFD significantly affect the precipitation simulation in the Southeastern China with complex sub‐grid terrains. This research emphasizes the crucial role of the remote effects of the STOFD. Key Points: Local (remote) effects of the sub‐grid turbulent orographic form drag (STOFD) affect precipitation in the Southeastern (Northern) ChinaRemote effects of the STOFD strongly affect the atmospheric circulation and improve the precipitation simulation in the Northern ChinaLocal effects of the STOFD can enhance the precipitation in the Southeastern China by generating more concentrated disturbances [ABSTRACT FROM AUTHOR]

Temperature and water vapor are known to fluctuate on multiple scales. In this study 27 years of airborne measurements of temperature and relative humidity from In‐service Aircraft for a Global Observing System (IAGOS) are used to parameterize the distribution of water vapor in the upper troposphere and lower stratosphere. The parameterization is designed to simulate water vapor fluctuations within gridboxes of atmospheric general circulation models (AGCMs) with typical size of a few tens to a few hundred kilometers. The distributions currently used in such models are often not supported by observations at high altitude. More sophisticated distributions are key to represent ice supersaturation, a physical phenomenon that plays a major role in the formation of natural cirrus and contrail cirrus. Here the observed distributions are fitted with a beta law whose parameters are adjusted from the gridbox mean variables. More specifically the standard deviation and skewness of the distributions are expressed as empirical functions of the average temperature and specific humidity, two typical prognostic variables of AGCMs. Thus, the distribution of water vapor is fully parameterized for a use in these models. The new parameterization reproduces the observed distributions with a determination coefficient always greater than 0.917 and with a mean value of 0.997. The parameterization is robust to a selection of various geographical subsets of data and to gridbox sizes varying between 25 and 300 km. Plain Language Summary: Temperature and water vapor fluctuate in the atmosphere on different scales, from micrometers to thousands of kilometers. In this study we use airborne measurements of temperature and water vapor to study the spatial variability of humidity in the upper troposphere and lower stratosphere. The observations are used to build a simple modeling of water vapor distribution on scales from tens of kilometers to hundreds of kilometers, which is designed to be used in atmospheric general circulation models (AGCMs), the atmospheric components of Earth system models. This new modeling of water vapor fluctuations aims to increase the physical representation of cirrus clouds and aviation‐induced cloudiness in AGCMs. The observed water vapor distributions are modeled with a beta distribution, whose parameters are completely determined as empirical functions of two major variables of AGCMs, the average temperature in a gridbox, and the average water vapor in a gridbox. Overall, the modeled distributions fit those observed very well. Key Points: The fine‐scale distribution of water vapor in the upper troposphere is fully parameterized for use in atmospheric general circulation modelsThe parameterization is empirical and based on 257 million airborne observations made between 1995 and 2021This parameterization aims to improve the quality of the simulation of ice supersaturation, and the formation of cirrus and contrail clouds [ABSTRACT FROM AUTHOR]

The atmospheric circulation in the northern hemisphere interacts with that in the southern hemisphere mainly via lateral coupling and atmospheric mass exchanges across equator. Using the NCEP‐NCAR daily reanalysis over period 1979–2019, we examine the Inter‐Hemispheric Oscillation (IHO) on the synoptic timescale during boreal winter and its associations with Rossby waves by employing a 9‐day high‐pass filter and the time‐lag regression method. Our results demonstrate that the IHO exist in the surface air pressure anomalies on synoptic timescale which links to both the quasi‐stationary and migratory Rossby waves with large amplitudes in the mid‐ and high‐ latitudes from the troposphere up to the stratosphere. The synoptic‐IHO related quasi‐stationary waves appear mainly in zonal, roughly dominated by waves with wave‐number 1–7 at different latitudes. These waves disperse the wave energy eastward along westerly jet streams. On the other hand, the synoptic‐IHO related migratory Rossby waves are mainly observed in mid latitudes between 30°N–65°N and 30°S–60°S with stronger intensity in northern than in southern hemisphere. The phase speed of these waves is roughly estimated at about 9.5lon/d. The energy of intrinsic Rossby waves also propagates mainly eastward. The synoptic‐IHO has important impacts on surface air temperature via both the quasi‐stationary and migratory Rossby waves, inducing significant temperature changes over both Eurasian continent and North America as estimated from 40 winters. All the results are beneficial for us to better understand the IHO along with its interaction with Rossby waves and the formation mechanisms of cold weather and climate extremes during boreal winter. Plain Language Summary: The weather/climate extremes occur frequently in northern hemisphere as a result of the circulation variations on multitimescales. The circulation changes are partly related to atmospheric mass exchange between the northern hemisphere and southern hemisphere, which results in a phenomenon named as the Inter‐hemispheric Oscillations (IHO). Using the NCEP‐NCAR daily reanalysis from 1979 to 2019, we examined the IHO on synoptic timescale during boreal winter and its association with Rossby waves by employing the time‐lag regression method. Our results demonstrate that the IHO appears in zonal mean surface air pressure anomalies on synoptic timescale, which links to both the quasi‐stationary and migratory Rossby waves. The quasi‐stationary waves with larger amplitudes appear in middle latitudes, dispersing the wave energy eastward along westerly jet streams. On the other hand, the synoptic‐IHO‐related migratory Rossby waves move eastward with phase speed at about 9.5lon/d, also dispersing energy mainly eastward. The synoptic‐IHO significantly affects the wintertime surface air temperature via both the quasi‐stationary and migratory Rossby waves over Eurasian continent and North America. All these results are beneficial for us to better understand the IHO along with its interactions with Rossby waves and the formation mechanisms of weather and climate extremes during boreal winter. Key Points: Inter‐hemispheric Oscillations (IHO) of atmospheric mass is found to exist on synoptic timescale during boreal winterSynoptic‐IHO links to both the quasi‐stationary and migratory Rossby waves in the mid and high latitudesSurface weather and climate in mid to high latitudes are possibly influenced by synoptic IHO via both stationary and migratory Rossby waves [ABSTRACT FROM AUTHOR]

The European summer (June–August) 2022 was characterised by warm and dry anomalies across much of the continent, likely influenced by a northward‐shifted jet stream. These general features were well predicted by European Centre for Medium‐Range Weather Forecasts' system 5 seasonal forecast, initialised on May 1. Such successful predictions for European summers are relatively uncommon, particularly for atmospheric circulation. In this study, a set of hindcast experiments is employed to investigate the role that initialisation of the ocean, atmosphere, and land surface played in the 2022 forecast. We find that the trend from external forcing was the strongest contributor to the forecast near‐surface temperature anomalies, with atmospheric circulation and land‐surface interactions playing a secondary role. On the other hand, atmospheric circulation made a strong contribution to precipitation anomalies. Modelled Euro‐Atlantic circulation anomalies in 2022 were consistent with a La Niña‐forced teleconnection from the tropical Pacific. However, a northward jet trend in the model hindcasts with increasing greenhouse gas concentrations also contributed to the predicted circulation anomalies in 2022. In contrast, the observed linear trend in the jet over the past four decades was a southward shift, though it is unclear whether this trend was driven by external forcings or natural variability. Nevertheless, this case study demonstrates that important features of at least some European summers are predictable at the seasonal time‐scale. [ABSTRACT FROM AUTHOR]

The southern slope of the Tibetan Plateau (SSTP) is one of the rainiest regions in the world where geological hazards caused by extreme precipitation often occur. This study investigates the characteristics and mechanisms of extreme precipitation over SSTP from June to September during 2001–2020 using Global Precipitation Measurement satellite observation. The extreme precipitation days are defined as the days with top 5% of regional‐mean daily precipitation over SSTP in this period, which has an average precipitation of 27.2 mm/d. Averaging over the extreme precipitation days, precipitation peaks at an altitude of about 300 m, coinciding with the climatological maximum precipitation, but with a much larger value of 37.2 mm/d than the climatology of 11.9 mm/d. Composite analysis of circulations on extreme days reveals significant circulation anomalies in both the lower and upper troposphere. Specifically, the lower‐tropospheric circulations are characterized by significant westerly anomalies over northern India, and the upper‐tropospheric circulations are characterized by northerly anomalies over the central Tibetan Plateau, which are statistically independent. The lower‐tropospheric westerly anomalies blowing toward SSTP are blocked by the topography, favoring extreme precipitation over SSTP. The upper‐tropospheric northerly anomalies, on the other hand, correspond to anomalous northeasterlies north of SSTP in the middle troposphere and southeasterlies to the south in the lower troposphere, and the convergence of these circulation anomalies favors extreme precipitation over SSTP. Lastly, the lower‐tropospheric westerly and upper‐tropospheric northerly anomalies, respectively, correspond to less precipitation over the South Asian monsoon region and the Tibetan Plateau. Plain Language Summary: The southern slope of the Tibetan Plateau (SSTP) is one of the rainiest regions in the world, because huge amount of water vapor transported by the South Asian monsoon are blocked by the steep Himalayas. Extreme precipitation occurs frequently over SSTP, which causes geological hazards and threatens people's lives there. A comprehensive understanding of the disaster‐producing extreme precipitation over SSTP will be helpful for weather prediction and disaster mitigation. In this study, the extreme precipitation days are defined as the days with top 5% of regional‐mean daily precipitation over SSTP from June to September during 2001–2020. Spatiotemporal characteristics of extreme precipitation over SSTP and the associated atmospheric circulations are investigated. Results show that extreme precipitation peaks at about 300 m in elevation, where it is about triple the climatological mean, and the precipitation decreases sharply as elevation increases. The composited circulations on extreme days exhibit significant lower‐tropospheric westerly anomalies over northern India and upper‐tropospheric northerly anomalies over the central Tibetan Plateau. These two wind anomalies are climatologically independent of each other and both are significantly positively correlated with the SSTP extreme precipitation. Key Points: The 95% extreme precipitation over the southern slope of Tibetan Plateau (SSTP) peaks at ∼300 m where it is triple the climatological meanExtreme precipitation over SSTP is associated with lower‐tropospheric westerly and upper‐tropospheric northerly anomaliesThese circulation anomalies favor the extreme rainfall through topographic blocking and lower‐mid‐tropospheric convergence [ABSTRACT FROM AUTHOR]

An unprecedented heavy rainfall event in China ("21.7" extreme rainfall event) was simulated using the global variable‐resolution model (MPAS‐Atmosphere) across the scales (4, 8, 16 and 50 km). Although almost all experiments at different resolutions reproduce the spatiotemporal characteristics of precipitation, the simulated precipitation intensity from high to low is 16, 8, 50, and 4 km, with the 16 km simulation being closest to the observations. Precipitation magnitude is prominently influenced by the difference in simulated large‐scale circulation across a range of grid spacings. Further analysis revealed that the differences in latent heating across scales affect the geopotential height and wind field by altering temperature. The latent heating in 4 km simulation is the minimum while the 16 km simulation is maximum. More latent heating release leads to the low‐level pressure depression, amplifies the water vapor flux convergence, produces stronger upward motion and more clouds, and ultimately results in stronger precipitation. The sensitivity experiments for turning off latent heating tendencies during the event showed that the latent heat release has positive feedback on the "21.7" heavy rainfall event. This study highlights the importance of scale‐awareness of latent heat at different resolutions and suggests that the difference in simulated latent heat release during the event is the main reason for simulated different atmospheric circulation and precipitation across scales. Plain Language Summary: Due to the advancements in the numerical computing power, numerical weather prediction models (NWP) are operating at horizontal grid spacing ranging from 1 to 10 km. This study evaluates the simulation performance of the global variable‐resolution model MPAS‐A for a heavy precipitation event and investigates the influence of scale‐aware convective parameterizations on modeling rainfall at horizontal resolutions across the scales (4, 8, 16 and 50 km). The results show that 4 km simulation exhibits the weakest precipitation while the simulated precipitation at 16 km is the strongest. The difference in precipitation simulated by four experiments across scales derives from the variations in large‐scale circulation simulated with different refined resolutions. Further analysis revealed that the differences in latent heat at different resolutions ultimately lead to the changes in geopotential height and large‐scale wind field by altering temperature. 4 km experiment simulates less latent heat than other lower‐resolution experiments. Owing to the positive feedback of the latent heat release on precipitation, 4 km experiment simulates the minimum precipitation. This work highlights that latent heat plays a vital role in simulation of synoptic condition and precipitation. Key Points: Precipitation is influenced by the difference in simulated atmospheric circulation across a range of grid spacingsThe differences in simulated latent heat release across scales affect the geopotential height and wind field by altering temperatureThe latent heat release has positive feedback impact on the "21.7" heavy precipitation event [ABSTRACT FROM AUTHOR]

Persistent positive sea surface temperature anomalies (SSTAs) in the mid‐latitude Northeast Pacific (NEP), also known as "warm blob" or "marine heatwave," have substantial ecological and climate effects. This study delves into the spatiotemporal connection between Arctic Oscillation (AO) and SSTAs in the NEP. First, we conduct the lead‐lag correlation and maximum covariance analyses to disentangle the closest temporal relationship between October AO and wintertime SSTAs in the NEP. Then, we categorize the years in positive AO (pAO) phase into two groups: positive AO with warm anomaly (pAO&Blob) group and positive AO without warm anomaly (pAO&noBlob) group based on the October AO index and wintertime blob index. Results show that the positive phase of AO in October strongly influences the wintertime warm SSTAs in the NEP through local and remote pathways. The local pathway is contingent upon the longitudinal positioning of AO‐related high‐pressure anomaly (i.e., anomalous ridge) in the North Pacific. When easterly anomalies prevail at the southern flank of the anomalous ridge over the NEP, they foster warm SSTAs in the NEP. However, different locations of the high‐pressure anomalies may impede the NEP warming. Remote pathways indicate the teleconnections triggered by AO‐related precipitation increase in Greenland and decrease in East Asia, sustaining the high‐pressure anomaly and promoting the anomalous NEP warming. Hence, this study presents new evidence on polar and mid‐latitude climate connections, which may provide potential predictability for the warm SSTAs in the NEP. Plain Language Summary: Under rapid climate change, long‐lasting warm sea surface temperature anomalies (SSTAs) in the mid‐latitude Northeast Pacific (NEP) have attracted wide attention due to their substantial ecological and climate effects. Arctic Oscillation (AO) is the dominant mode of atmospheric circulation variability in mid‐to‐high latitudes of the Northern Hemisphere. Its positive phase is featured by a low‐pressure center in the Arctic region and high‐pressure centers in the mid‐latitude regions. Our results reveal a robust connection between the positive phase of AO in October and warm SSTAs in the NEP during winter. We identify two primary pathways through which the October AO influences the wintertime sea surface temperature (SST) warming in the NEP. Locally, a high‐pressure anomaly over the NEP is associated with easterly wind anomalies to its southern flank, which diminish oceanic latent heat loss to the atmosphere, thus fostering the SST warming in the NEP. However, other locations of the high‐pressure anomaly related to AO may not be favorable for the warming of the NEP. From a remote view, AO can impact the NEP SST through teleconnections due to increased precipitation in Greenland and decreased precipitation in East Asia, sustaining the high‐pressure anomaly over the NEP and further bolstering the NEP warming. Key Points: Temporally, Arctic Oscillation (AO) in October is closely linked to wintertime sea surface temperature (SST) anomalies in the mid‐latitude Northeast Pacific (NEP)The AO‐related anomalous ridge located over the NEP is favorable for the warming of SST locallyRemotely, enhanced rainfall in Greenland and decreased rainfall near East Asia sustain the anomalous ridge over the NEP via teleconnection [ABSTRACT FROM AUTHOR]

A 38‐year aerosol optical thickness (AOT) satellite product from the Advanced Very High‐Resolution Radiometer (AVHRR) is used to investigate the aerosol variabilities in the North Indian Ocean (NIO). A dipolar mode with a notable meridional contrast between the equatorial and northern NIO is revealed by the second mode of Empirical Orthogonal Function (EOF) analysis with a sharp rise over the Arabian Sea (AS) and Bay of Bengal (BoB) since 2002. Our results show that the aerosol dipolar variation is primarily modulated by an El Niño–Southern Oscillation (ENSO) during 1983–2001 (ID1) and by a warm phase of Atlantic Multi‐decadal Oscillation (AMO) during 2002–2020 (ID2), leading to a dry‐and‐warming condition spanning the coasts of East Africa, the Arabian Peninsula (AP), and South Asia (SA) that favors increasing aerosol emission and a longer life cycle in the upstream regions. A warm phase of the AMO tends to excite an anomalous cyclone in western Siberia and reinforces anticyclonic circulation in the Tibetan Plateau. Correlation analyses between the second EOF mode time series and other parameters in ID1 and ID2 show that an interannual dry‐and‐warming condition over the AP–SA is associated with a noticeable north‐south contrast of convection between the equatorial NIO and AP–SA in ID1. But in ID2, a zonal contrast of anomalous convective activities between the AP–SA and the BoB‐South China Sea is dominant, partially due to the warming AMO, which aids the development of anticyclonic cells over the TP and the strengthened subtropical westerly jet streams. Plain Language Summary: Using satellite aerosol observations during 1983–2020 and a multivariate statistical technique for temporal‐spatial analysis, we explored the aerosol long‐term and year‐by‐year variations in the North Indian Ocean (NIO). Our results show a significant rise in springtime aerosol over the Arabian Sea and Bay of Bengal since the early 2000s, which is attributed to intensification of a dry‐and‐warming condition in the coasts of East Africa, the Arabian Peninsula, and South Asia. A relatively low aerosol concentration before the early 2000s is mainly modulated by the anomalies of sea surface temperature (SST) in both the West and East Pacific associated with an El Niño or La Niña event, but an increasing aerosol concentration after the early 2000s is linked to warmer SST associated with a phenomenon called Atlantic Multi‐decadal Oscillation (AMO). A warm phase of the AMO may aid the development of the remote teleconnection pattern in the midlatitude regions of the Northern Hemisphere, and thus reinforce the anomalies of atmospheric circulation in the subtropical regions. Key Points: A notable springtime aerosol rise over the Arabian Sea and Bay of Bengal (ASBoB) since the early 2000s is revealed by using satellite dataThe El Niño events may cause a relatively low aerosol loading over the ASBoB during 1983–2001A warm‐phase Atlantic Multi‐decadal Oscillation may favor a notable high aerosol loading over the ASBoB during 2002–2020 [ABSTRACT FROM AUTHOR]

The Jurassic/Cretaceous transition was characterized by several distinct palaeoenvironmental processes and events, amongst which some of the best known are the late Tithonian–early Berriasian aridization and the late Berriasian tectonic reactivation in the Neotethyan Collision Belt. This study aims to reconstruct the latest Jurassic–earliest Cretaceous palaeoenvironment and its evolution in the area of the Transdanubian Range (Hárskút and Lókút successions, Hungary), and provide new data on the relation between climate changes, palaeoceanography and marine ecosystems. Herein, calcareous nannofossil and geochemical data are presented and put into a geochronological framework in order to evaluate and compare palaeoenvironmental signals recorded in the two studied successions; the resultant scenario is compared with published literature data from both the western Tethyan region and northern Europe. Accordingly, in the Transdanubian Range, the relatively humid climate of the early Tithonian was followed by the late Tithonian–early Berriasian arid phase and the late Berriasian humidification. Besides, two intervals of palaeoceanographic perturbations were documented in the upper Tithonian–lowermost Berriasian (OD I), and the lower/upper Berriasian transition beds (OD II); these are manifested by the record of seafloor hypoxia and elevated accumulations of micronutrients, as well as changes in calcareous nannofossil assemblages. In the view of this study, the most probable trigger of the late Tithonian–early Berriasian aridization was a restriction in the atmospheric circulation (including monsoons), which was forced by climate cooling and lowering thermal gradient between landmasses and the ocean. Under such conditions, the mechanism of a wind‐induced water mixing might become less efficient, driving seawater stratification, seafloor hypoxia and increased burial of nutrients. Although the humid climate of the late Berriasian likely resumed the monsoon‐type circulation, the tectonic reactivation and uplift in the NeoTethyan Collision Belt might have effectively separated the Bakony Basin from the 'open' NeoTethys, which hampered the marine circulation and efficient water mixing in the former. [ABSTRACT FROM AUTHOR]

Subseasonal forecast models are shown to suffer from the same inconsistency in the signal‐to‐noise ratio evident in climate models. Namely, predictable signals in these models are too weak, yet there is a relatively high level of agreement with observed variability of the atmospheric circulation. The net effect is subseasonal forecast models show higher correlation with observed variability than with their own simulations; that is, the signal‐to‐noise paradox. Also, similar to climate models, this paradox is particularly evident in the North Atlantic sector. The paradox is not evident in week 1 or week 2 forecasts, and hence is limited to subseasonal time‐scales. The paradox appears to be related to an overly fast decay of northern annular mode regimes. Three possible causes of this overly fast decay and for the paradox in the Northern Hemisphere are identified: a too‐fast decay of polar stratospheric signals, overly weak downward coupling from the stratosphere to the surface in some models, and overly weak transient synoptic eddy feedbacks. Though the paradox is clearly evident in the North Atlantic, it is relatively muted in the Southern Hemisphere: southern annular mode regimes persist realistically, the stratospheric signal is well maintained, and eddy feedback is, if anything, too strong and zonal. [ABSTRACT FROM AUTHOR]

During the 2022 Asian summer monsoon, the climatological driest parts of Sindh and Balochistan provinces in southwestern Pakistan and the northern Arabian Sea (regions of climatological heat low, HLOW) experienced unprecedented precipitation (>500% of the normal) whereas precipitation was reduced from the Indo‐Gangetic Plain to the tropical western Pacific. Our working hypothesis is that the weakened large‐scale monsoon is a direct response to tropical sea‐surface temperature: wave responses that develop in response to changes in diabatic heating anomalies over the regional precipitation centers within the Asian monsoon intensify and transition HLOW into an anomalous moist low. To validate the hypothesis, process‐oriented diagnostics are applied to European Centre of Medium‐range Weather Forecasts Reanalysis v5 (ERA5), and numerical experiments are performed with a linear atmospheric general circulation model. Model solutions confirm that the weakened large‐scale monsoon, essentially a linear response, is determined by persistent warm sea‐surface temperature and enhanced precipitation anomalies over the equatorial and southeastern Indian Ocean–Maritime Continent, and Rossby waves emanating from there, and from continental India, deepen the HLOW. Concomitantly, as a Rossby wave response to negative precipitation anomalies over the northern Bay of Bengal and Indochina during June, and their poleward migration during July–August, positive height anomalies develop and intensify over northern India. The resultant horizontal pressure gradient between HLOW and northern India drives concentrated low‐level wind anomalies that are efficient in advecting the strongest climatological moisture gradient to precondition the lower troposphere during June, and in determining the unprecedented precipitation during July–August when the seasonal cycle prevails over HLOW. Model sensitivity to horizontal moisture advection confirms ERA5 diagnostics. Nearly identical tropical forcing and large‐scale weakened monsoon responses are observed during 2010 and 2020. In these years, diagnostics identify subtle changes in latitudinal position of negative precipitation anomalies over the Bay of Bengal and Indo‐Gangetic Plain that lead to lesser contribution by horizontal moisture advection, resulting in weaker positive precipitation anomalies over southwest Pakistan. [ABSTRACT FROM AUTHOR]

Our previously described reformulation of the Met Office's dynamical core for weather and climate prediction is extended to spherical domains using a cubed‐sphere mesh. We update the semi‐implicit mixed finite‐element formulation to be suitable for spherical domains. In particular, the finite‐volume transport scheme is extended to take account of non‐uniform, non‐orthogonal meshes and uses an advective‐then‐flux formulation so that increment from the transport scheme is linear in the divergence. The resulting model is then applied to a standard set of dry dynamical core tests and compared with the existing semi‐implicit semi‐Lagrangian dynamical core currently used in the Met Office's operational model. [ABSTRACT FROM AUTHOR]

The regional climate of New Zealand's South Island is shaped by the interaction of the Southern Hemisphere westerlies with the complex orography of the Southern Alps. Due to its isolated geographical setting in the south‐west Pacific, the influence of the surrounding oceans on the atmospheric circulation is strong. Therefore, variations in sea surface temperature (SST) impact various spatial and temporal scales and are statistically detectable down to temperature anomalies and glacier mass changes in the high mountains of the Southern Alps. To enable future studies on the processes that govern the link between large‐scale SST and local‐scale high‐mountain climate, we utilized dynamical downscaling with the Weather Research and Forecasting (WRF) model to produce a regional atmospheric modelling dataset for the South Island of New Zealand over a 16‐year period between 2005 and 2020. The 2 km horizontal resolution ensures realistic representation of high‐mountain topography and glaciers, as well as explicit simulation of convection. The dataset is extensively evaluated against observations, including weather station and satellite data, on both regional (in the inner domain) and local (on Brewster Glacier in the Southern Alps) scales. Variability in both atmospheric water content and near‐surface meteorological conditions is well captured, with minor seasonal and spatial biases. The local high‐mountain climate at Brewster Glacier, where land use and topographic model settings have been optimized, yields remarkable accuracy on both monthly and daily time scales. The data provide a valuable resource to researchers from various disciplines studying the local and regional impacts of climate variability on society, economies and ecosystems in New Zealand. The model output from the highest resolution model domain is available for download in daily temporal resolution from a public repository at the German Climate Computation Center (DKRZ) in Hamburg, Germany (Kropač et al., 2023; 16‐year WRF simulation for the Southern Alps of New Zealand, World Data Center for Climate (WDCC) at DKRZ [data set]. https://doi.org/10.26050/WDCC/NZ‐PROXY_16yrWRF). [ABSTRACT FROM AUTHOR]

We describe the transcription and quality control processes for rescuing around 570,000 sub‐daily and daily weather observations which were recorded in the UK Met Office Daily Weather Reports during the 1861–1875 period. These data are from the start of coordinated weather observations and were collected with the aim of making the first‐ever weather forecasts. The observations were rescued thanks to 3500 volunteers and include sub‐daily sea‐level pressure, dry and wet bulb temperatures, daily maximum and minimum temperatures, and daily rainfall amounts from 70 different locations across Western Europe, and one in Canada. We highlight how these observations will be used to fill gaps in existing pressure and temperature datasets and use two case studies to show how the pressure observations will likely better constrain the atmospheric circulation during two severe storms. We also compare a sub‐sample of the newly rescued observations with data that were previously digitized for a small number of locations for the same dates, finding good agreement in general, although some discrepancies remain. [ABSTRACT FROM AUTHOR]

Flash droughts (FDs) are distinguished by a rapid development associated with strong precipitation deficits and/or increases in atmospheric evaporative demand in the short‐term, but little is known about the atmospheric conditions underlying these events. In this study, we analyse for the first time the atmospheric dynamics involved in the development of FDs in Spain over the period 1961–2018. FDs are related to large‐scale atmospheric circulation patterns affecting the region, in particular with the positive phase of the North Atlantic Oscillation (NAO). The NAO is the main atmospheric driver of FDs in winter and autumn, and it is essential in explaining FD development in spring. We also found that FDs are typically linked to strong positive anomalies in 500 hPa geopotential height and sea level pressure over the region during the weeks prior to the onset. At the synoptic scale, the most common weather types (WTs) recorded during the development of FDs are Anticyclonic Western (ANT_W_AD), East (E_AD) and Northeast (NE_AD) advection, and Anticyclonic (ANTICYC). In particular, ANTICYC WT is the main atmospheric driver of FDs in summer. Ridging conditions occur frequently during FDs in all seasons, being the most important factor controlling FD development in spring. Likewise, we noted that some of the FDs recorded in summer are related to and/or exacerbated by Saharan air intrusions associated with pronounced ridges. The results of this research have important implications for the understanding, monitoring and prediction of FDs in Spain, providing a detailed assessment of the main atmospheric dynamics involved in FD triggering at different spatial scales. [ABSTRACT FROM AUTHOR]

ERA5 reanalysis data, precipitation data from China, and National Oceanic and Atmospheric Administration (NOAA) monthly sea surface temperature (SST) data are used to analyse the impact of the meridional position of the East Asian subtropical jet (EASJ) on summer precipitation in China and its correlation with Atlantic SST. The results indicate that when the EASJ significantly shifts northward, the western North Pacific subtropical high (WNPSH) weakens with an eastward displacement. Upper‐level convergence and moisture divergence, corresponding to descending motion, lead to decreased precipitation in the Yangtze River Valley (YRV). Meanwhile, upper‐level divergence occurs over South China (SC), the Hexi Corridor (HC), and Northeast China (NEC), where moisture converges and ascends, favouring an increase in precipitation. Conversely, when the EASJ undergoes a significant southward shift, the WNPSH strengthens and expands westward. Opposing atmospheric circulation patterns in these four regions result in reversed precipitation anomalies compared with those observed when the jet shifts northward. The meridional position of the EASJ is closely related to the summer subtropical Atlantic SST. The positive (negative) SST anomaly (SSTA) over the subtropical Atlantic induces negative (positive) geopotential height anomaly in the upper troposphere over the North Atlantic by modulating the atmospheric meridional circulation. Geopotential height anomalies trigger eastward‐propagating Rossby waves, generating anomalous cyclones and anticyclones over East Asia. These anomalous cyclones and anticyclones lead to zonal wind anomalies, which alter the strength of the westerlies on both sides of the climatological jet axis, thereby changing the jet's meridional position. Additionally, the difference in the propagation direction of wave activity flux between positive and negative SSTA alters the distribution of wave energy convergence and divergence in the EASJ region, further affecting the intensity of the average westerly winds on both sides of the climatological jet axis, ultimately producing the changes in the meridional position of the EASJ. [ABSTRACT FROM AUTHOR]

In July 2021, a cut‐off low‐pressure system brought extreme precipitation to Western Europe. Record daily rainfall totals led to flooding that caused loss of life and substantial damage to infrastructure. Climate change can amplify rainfall extremes via thermodynamic processes, but the role of dynamical changes is uncertain. We assess how the dynamics involved in this particular event are changing using flow analogues. Using past and present periods in reanalyses and large ensemble climate model data of the present‐day climate and 2°C warmer climate, we find that the best flow analogues become more similar to the cut‐off low‐pressure system observed over Western Europe in 2021. This may imply that extreme rain events will occur more frequently in the future. Moreover, the magnitude of the analogue lows has deepened, and the associated air masses contain more precipitable water. Simulations of future climate show similar events of the future could lead to intense rainfall further east than in the current climate, due to a shift of the pattern. Such unprecedented events can have large consequences for society, we need to mitigate and adapt to reduce future impacts. [ABSTRACT FROM AUTHOR]

Heatwaves represent a significant and growing threat to natural ecosystems and socio‐economic structures, making heatwave risk mitigation and prevention an important area of research. In exploring heatwave frequency and intensity from 1901 to 2020, the present study finds a sharp increase in both. The study also finds that the spatial distribution of heatwaves is unequal, the volatility of intensity characteristics has become more prominent over time, and the Gini coefficients of four key heatwave indictors have become larger due to increasing dryness. Although heatwaves occur more frequently in drylands, there is greater cumulative heat in humid areas, resulting in a higher heatwave risk in those areas. The global heatwave risk over the past three decades (1991–2020) has increased nearly five‐fold compared to the early 20th century (1901–1930). Furthermore, GeoDetector analysis indicates that the Palmer drought severity index (PDSI) and downward surface shortwave radiation (Srad) contributing the most in drylands and humid areas (0.29 and 0.41, respectively). The contribution of relative humidity (RH), wind speed (WS), soil moisture (SM), and the normalized difference vegetation index (NDVI) is also significant in humid areas, but is much smaller in drylands. Composite analysis shows that the years with anomalously high heatwave risk correspond to positive anomalies of 500hPa geopotential height and surface pressure. The inhibition of cloud formation due to sinking air and the resulting increase in temperature in the atmosphere may be increasing the risk of heatwave occurrence. This study emphasizes the urgent need to address worsening climate change impacts. Plain Language Summary: Heatwaves are high‐impact extreme events, and their monitoring, risk assessment, and countermeasure development are critically important. This study focuses on the evolution of heatwaves, including their risk assessment and driving mechanisms, based on Gini coefficients, GeoDetector, and composite analysis. It is found that heatwaves have become more frequent and intense over the past 120 years (1901–2020), and their occurrence rate has increased five‐fold. After 1980, heatwave characteristics (frequency, intensity, duration, and severity) increased in volatility and their spatial distribution showed an increase in inequality. Interestingly, while drylands experience more heatwaves, humid areas accumulate more heat, leading to a higher risk of heatwaves in humid areas. In fact, the intensity of heatwave risk is 7.7% higher in humid areas than in drylands, with factors such as relative humidity, wind speed, soil moisture, and the normalized difference vegetation index contributing more in humid areas than in drylands. The study also relates these changes to atmospheric circulation, which is typically characterized by higher upper atmospheric pressure and surface pressure, leading to reduced cloud formation and higher temperatures. Our study of heatwave risk highlights the increasing impacts of climate change and the need for urgent action, especially in humid areas. Key Points: Heatwaves are more frequent in drylands, but cumulative heat is greater in humid areasHeatwave risk has quintupled over one century and is higher in humid areas than in drylandsHigh heatwave risk is usually accompanied by anticyclonic anomalies [ABSTRACT FROM AUTHOR]

Electron precipitation, a crucial link between Earth's magnetosphere and atmosphere, profoundly influences the coupled magnetosphere‐ionosphere‐atmosphere system. Existing models of the ring current often rely on electron lifetimes for characterizing the effects of pitch‐angle scattering, thus limiting accurate predictions of loss cone dynamics. This study introduces a method called steady‐state approximation (steady state approximation) utilizing the steady‐state solution of the pitch‐angle diffusion operator to calculate pitch angle resolved flux within the loss cone. The method enables precise comparisons with low‐earth orbit satellite measurements to validate parameterized electron lifetimes. Applying this approach to reevaluate a prior study, we uncover underestimated electron precipitation during geomagnetic storms, particularly in the pre‐midnight sector. This discrepancy reveals a previously overlooked loss process. Our method enhances the fidelity of global magnetospheric simulations, contributing to improved predictions of ionospheric conductance and atmospheric chemistry dynamics. Key Points: We introduce a method called steady state approximation (SSA) to calculate flux within the loss cone from Fokker‐Planck simulationsThe SSA shows good agreement with 1D pitch‐angle diffusion simulationsApplying the SSA confirms a large underestimation of modeled electron precipitation in the pre‐midnight sector during storms [ABSTRACT FROM AUTHOR]

As a key dynamic element of the Bjerknes feedback mechanism, the thermocline effect (TE) is critically important to El Niño modeling. In this study, the potential influence of TE‐related parametric uncertainties on El Niño is investigated using the conditional nonlinear optimal parametric perturbation (CNOP) method based on an intermediate coupled model (ICM). The optimal perturbation of the TE‐related parameter (OTEP), which substantially affects El Niño simulations, is estimated through the CNOP approach. Results reveal that the El Niño simulation is highly sensitive to the TE uncertainty in the eastern equatorial Pacific, with OTEP‐induced simulation errors demonstrating an El Niño‐like growth trend. On one hand, as indicated by the simulated El Niño intensity, the uncertainty in the TE in the eastern region can easily affect the strength of the Bjerknes feedback‐related thermocline effect and atmospheric circulation. On the other hand, the enhanced TE is highly favored to accelerate the growth of the SST error due to the air–sea interaction, thus severely affecting the El Niño simulations. Therefore, adequately representing the TE in the equatorial eastern Pacific is emphasized for effectively improving El Niño simulations. Plain Language Summary: Thermocline effect (TE) uncertainty seriously challenges numerous climate models. Focusing on the TE‐related parameter in an intermediate coupled model, this study quantitatively examines the impact of the TE on El Niño simulations. The spatial structure of the TE‐related parameters that cause the largest simulation errors is determined by employing an optimization algorithm (conditional nonlinear optimal parametric perturbation). Subsequently, a systematic analysis of the error scenarios resulting from these optimal TE‐related parameters is conducted with their underlying mechanisms being explored. Results indicate that the uncertainties in the TE in the eastern tropical Pacific tend to alter the intensity of the positive Bjerknes feedback, leading to considerable errors in El Niño simulations. Furthermore, these simulation errors are intensified by air–sea interactions. This study provides vital theoretical insights for augmenting the precision of ENSO predictions. Key Points: El Niño simulation is sensitive to the model uncertainty in the thermocline effect (TE) in the eastern equatorial PacificThe TE uncertainty‐related effects on vertical advection and Kelvin wave act to amplify El Niño warming, thus causing large simulation errorsThe simulation error in El Niño due to TE uncertainty is further increased by air–sea interaction (more than 30%) [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs), extreme warm ocean temperature events, greatly impact marine ecosystems. While most MHW studies in the South China Sea (SCS) focus on the sea surface, subsurface characteristics remain less explored. This study uses high‐resolution (1/12°) ocean reanalysis data sets to assess MHW properties with depth in the SCS from 1993 to 2022. We find that MHW intensities are typically stronger at subsurface levels (30–150 m) than at the surface, with significant spatial variations. The vertical structures of MHW maximum and cumulative intensities peak between 70 and 100 m with 2.7°C and 63°C days, respectively; MHW annual days and duration increase gradually from 10 to 2,000 m with duration peaks at 2,000 m (∼60 days), four times longer than that at the surface. The SCS experienced two major periods of extensive El Niño‐related subsurface MHWs from 1997 to 2002 and 2008 to 2014, with MHWs reaching depths of 150 m and covering 70% of the upper 40 m. Strong El Niño events strengthen the western Pacific subtropical high, reducing summer monsoon winds, weakening coastal upwelling east of Vietnam, and increasing water temperatures. Regions of elevated eddy kinetic energy in the SCS suggest that significant mesoscale eddy activities are situated east of Vietnam. In addition, notable eddy heat transport was observed in the above region and west of the Luzon Strait in the upper 1,000 m. This may help to explain the high maximum and cumulative intensities of MHWs exceeding 100 m in the northern SCS. Plain Language Summary: Marine heatwaves (MHWs) have caused significant biological and socioecological impacts around the globe due to accelerated ocean warming. Most MHW studies have focused primarily on sea surface temperature extremes, while the subsurface impacts of MHWs have yet to be evaluated. In this study, we use high‐resolution (1/12°) ocean reanalysis data sets to estimate the statistical properties and potential mechanisms of MHWs from the surface to 2,000 m in the South China Sea (SCS) from 1993 to 2022. The results show that the maximum and cumulative intensities of MHWs are typically more intense in the subsurface at 30–150 m with significant spatial variations and that their annual days and duration increase with depth. Similarly, the vertical structures of maximum and cumulative intensities rapidly become strongest at depths between 70 and 100 m, reaching a maximum at 2.7°C and 63°C days, respectively. The SCS has experienced two major periods of widespread and persistent El Niño‐related subsurface MHWs, with the deepest reaching 150 m and covering 70% of the upper 40 m. Mechanistically, atmospheric circulation and ocean mesoscale eddy activity contribute to the intensification of subsurface MHWs in the SCS. Key Points: The maximum and cumulative intensities of marine heatwaves (MHWs) are significantly greater at the subsurfaceMHWs regularly extend into the deep ocean during the strengthened western Pacific subtropical high driven by strong El Niño eventsOcean eddy heat transport may be responsible for high‐intensity MHWs below 100 m in the northern South China Sea [ABSTRACT FROM AUTHOR]

The variability of chlorophyll (Chla) in the Southern Tropical Indian Ocean (STIO) is not fully understood. This study utilized biogeochemical Argo (BGC‐Argo) and satellite observations to investigate the seasonal Chla variations in the upper layer (above 200 m) and their relationships to physical dynamics. The results indicate the existence of a well‐developed deep Chla maximum (DCM) layer situated between depths of 50 and 150 m. The shallowest DCM was at the Seychelles‐Chagos thermocline ridge because of permanent upwelling. Both the northern (4°S–12°S, 52°E−92°E) and southern (12°S–25°S, 52°E−92°E) regions experience surface blooms during July–August. However, they exhibit distinct Chla changes in response to different physical processes and nitrate concentrations below the mixed layer. In the northern region, the thermocline plays a critical role in regulating DCM depth and intensity. From April to June, subsurface upwelling and near‐surface stratification processes promote nutrient and Chla accumulation in the subsurface layer, resulting in elevated surface Chla levels in the subsequent months. In contrast, the southern region is characterized by oligotrophic conditions, where light availability primarily governs Chla variability below the mixed layer. Specifically, from November to January, when light intensity intensifies, Chla increases below the mixed layer. Furthermore, BGC‐Argo data revealed a long‐lived cyclonic eddy that facilitated the westward transport of Chla, significantly contributing to surface Chla blooms through eddy‐pumping and eddy‐trapping mechanisms. This research elucidates the fundamental characteristics of Chla distribution from a three‐dimensional perspective and furthers our understanding of the complex biophysical interactions within the STIO. Plain Language Summary: The vertical distribution of chlorophyll in open ocean regions is often uneven. Due to the optimal availability of nutrients and light, the maximum chlorophyll layer predominantly exists in the subsurface layer. Understanding chlorophyll variations in the upper water column of the Southern Tropical Indian Ocean (STIO) has been limited by its remote location. Our findings, derived from satellite and biogeochemical float data, indicate that a prominent deep chlorophyll maximum (DCM) layer is a key feature in the STIO, with its depth ranging from 50 to 150 m and influenced by both light intensity and atmospheric dynamics. The shallowest DCM is found in the Seychelles‐Chagos thermocline ridge. In the STIO, surface chlorophyll increases during July‐August as the mixed layer deepens. However, due to differing physical dynamics and nitrate concentrations, chlorophyll variability below the surface layer differs across regions. Additionally, biogeochemical floats have observed a long‐lived mesoscale cyclonic eddy that enhances vertically integrated chlorophyll concentrations, demonstrating the combined effects of mesoscale eddies and wind‐driven mixing. This study provides new insights into chlorophyll distribution from a three‐dimensional perspective in the STIO and enhances our understanding of the interactions between biological and physical processes. Key Points: Biogeochemical Argo data are used to reveal the distinct deep chlorophyll maximum layer exists in the Southern Tropical Indian OceanThe characteristics and physical dynamics responsible for the observed chlorophyll variability are region‐dependentA case study revealed that the combined influence of eddies and surface mixing enhances chlorophyll concentration in the upper layer [ABSTRACT FROM AUTHOR]

There is a long history of observation and monitoring at local scales with a focus on meteorological modulation of lakes, however, the features at the local scale are heavily influenced by large‐scale atmospheric circulation. Harmful algal blooms (HABs) in large shallow eutrophic lakes are susceptible to local meteorological conditions, but their response to climate system variability is rarely considered. This study reveals that HABs in Lake Taihu, the third largest freshwater lake in subtropical China, are promoted by the weakened East Asian monsoon system in precursory early winter, but show no response in late winter with the low temperature unfavorable for algal metabolism. The weak early winter monsoon system is characterized as the northward‐shifted polar front jet and eastward‐tilted East Asian Trough. The accompanied anomalous descending motion decelerates surface winds over the middle to lower reaches of the Yangtze River including Taihu basin by strengthening atmospheric stratification and decreasing turbulent activity in the lower troposphere. The weakened surface winds reduce sediment resuspension and improve underwater light availability in Lake Taihu, providing favorable light condition for phytoplankton growth. It is indicated that the early‐winter surface winds rather than simultaneous nutrient supply, play a dominant role on the interannual variability of algal biomass in Lake Taihu. The positive algal biomass anomaly in early winter tends to persist and promote HABs in the following warmer seasons. Our finding validates the interannual teleconnection between climate system and HAB variation in Lake Taihu, and provides insights on predicting HABs in subtropical East Asian shallow lakes. Key Points: The algae in Lake Taihu are more susceptive to meteorological condition in early winter than in late winterEarly winter monsoon system modulates algal biomass by impacting local wind speed and underwater light conditionExtreme meteorological condition driven by remote climate variability could impact harmful algal blooms in East Asian shallow lakes [ABSTRACT FROM AUTHOR]

Paleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations. Key Points: This study establishes a new orbitally‐constrained chronology for International Ocean Discovery Program Site U1464Australian Northwest shelf sediments preserve ∼400 kyr eccentricity cycles in %CaCO3 and ∼41 kyr obliquity cycles in dust proxy recordsObliquity in Northwest Australian dust flux may be related to the East Asian winter monsoon and summer inter‐tropical insolation gradient [ABSTRACT FROM AUTHOR]

The hydrogen isotopic compositions of leaf‐wax n‐alkanes (δDalk) and n‐alkanoic acids (δDacid) reflect ambient climatic conditions (including precipitation δD values, δDprecip). However, the understanding of climatic conditions of exactly which period (i.e., early or entire period of the leaf's lifespan) these biomarkers preserve is still evolving. Previous studies on the δDalk and δDacid values, done only in extra‐tropical regions, mostly indicate that δDalk values are biased toward the early growing season whereas δDacid values are not biased toward any season. To decipher the seasonal bias in δDalk and δDacid records from tropics, we conducted a long‐duration experiment wherein deciduous and evergreen species were grown using normal water (δD = −2‰) during early stages of the leaf growth and later using isotopically labeled water (δD = 1,000‰). Our experiment revealed (a) in deciduous and evergreen species, δDalk and δDacid values reflect δDprecip during early stages of the leaf growth, (b) synchronous synthesis of n‐alkanes and n‐alkanoic acids, and (c) in deciduous species, minor incorporation of the previous year's photosynthates in leaf wax pool of the current year's mature leaves. Our study suggests that δDalk and δDacid records in the tropics are biased toward the climatic conditions prevailing during early stages of leaf growth. This bias should be considered while comparing the δDprecip values generated from leaf wax proxy records and isotope‐enabled atmospheric circulation models. Plain Language Summary: The hydrogen isotopic composition of leaf wax n‐alkanes and n‐alkanoic acids preserved in sediments have been used extensively for reconstructing past climate variability. However, whether these records reflect a climate of a specific season or an entire year is not known. In our experiment, we grew various tropical plants using normal water during early growing season and heavy water during later growing season. Lack of isotopic signal associated with the heavy water in leaf wax compounds suggested that the bulk of leaf wax production occurred during the early growing season of the leaves. As the hydrogen isotopic composition of the leaf wax compounds reflects ambient climatic conditions, our results suggested that the hydrogen isotope record of tropical leaf wax compounds reflects the climatic conditions prevailing during the early stages of leaf growth. Key Points: Hydrogen isotope records of leaf wax n‐alkane and n‐alkanoic acid from the tropics reflect climatic conditions during the early leaf growthBoth deciduous and evergreen leaf wax hydrogen isotope records are biased toward the early stages of the leaf growthThis bias should be considered while comparing the hydrogen isotope of precipitation generated from climate models and leaf wax records [ABSTRACT FROM AUTHOR]

Many super‐Earths are on very short orbits around their host star and, therefore, more likely to be tidally locked. Because this locking can lead to a strong contrast between the dayside and nightside surface temperatures, these super‐Earths could exhibit mantle convection patterns and tectonics that could differ significantly from those observed in the present‐day solar system. The presence of an atmosphere, however, would allow transport of heat from the dayside toward the nightside and thereby reduce the surface temperature contrast between the two hemispheres. On rocky planets, atmospheric and geodynamic regimes are closely linked, which directly connects the question of atmospheric thickness to the potential interior dynamics of the planet. Here, we study the interior dynamics of super‐Earth GJ 486b (R=1.34 $R=1.34$R⊕ ${R}_{\oplus }$, M=3.0 $M=3.0$M⊕ ${M}_{\oplus }$, Teq≈700 ${\mathrm{T}}_{\text{eq}}\approx 700$ K), which is one of the most suitable M‐dwarf super‐Earth candidates for retaining an atmosphere produced by degassing from the mantle and magma ocean. We investigate how the geodynamic regime of GJ 486b is influenced by different surface temperature contrasts by varying possible atmospheric circulation regimes. We also investigate how the strength of the lithosphere affects the convection pattern. We find that hemispheric tectonics, the surface expression of degree‐1 convection with downwellings forming on one hemisphere and upwelling material rising on the opposite hemisphere, is a consequence of the strong lithosphere rather than surface temperature contrast. Anchored hemispheric tectonics, where downwellings und upwellings have a preferred (day/night) hemisphere, is favored for strong temperature contrasts between the dayside and nightside and higher surface temperatures. Plain Language Summary: The tectonic processes occurring on super‐Earths, which are rocky exoplanets with masses exceeding that of Earth, may differ significantly from those observed on the terrestrial planets in our solar system. Many super‐Earths are also expected to be tidally locked to their host star, so that always the same hemisphere faces the star. Tidal locking can lead to a strong temperature contrast between the dayside and nightside surface. Here, we investigate the influence of such strong surface temperature contrasts on the interior dynamics and tectonic behavior of super‐Earth GJ 486b, which is one of the best characterized Earth‐mass planets to date. We determined the surface temperature contrast between the dayside and nightside by assuming different efficiencies of atmospheric heat transport and ran global climate models for a set of different atmospheric compositions. Our 2D mantle convection simulations reveal that hemispheric tectonics, where cold material sinks on one hemisphere and hot material rises on the other side, emerges regardless of the surface temperature contrast if the planet has a strong lithosphere. However, a significant surface temperature contrast and an overall higher surface temperature tend to anchor the sinking cold material and rising hot material to the dayside and nightside respectively. Key Points: The mantle dynamics of super‐Earth GJ 486b are governed by the strength of the lithosphere and the day‐night surface temperature contrastDegree‐1 convection is a consequence of the strong lithosphere, rather than the temperature contrast between the dayside and nightsideA strong surface temperature contrast between the dayside and nightside can anchor downwellings to one hemisphere [ABSTRACT FROM AUTHOR]

Prior research extensively investigates the delayed influence of El Niño‐Southern Oscillation (ENSO) events on subsequent summer climates, with persistent sea surface temperature anomalies (SSTAs) in remote tropical oceans serving as crucial pathways. This study unveils a previously overlooked midlatitude pathway. During the developing winter, El Niño events induce basin‐scale cold SSTAs in the central North Pacific, which can persist into the following summer. These anomalies significantly influence early‐summer atmospheric circulation by enhancing atmospheric baroclinicity and transient eddy activities. Primarily driven by transient eddy vorticity forcing, an equivalent barotropic geopotential low anomaly emerges over the North Pacific. Enhanced by the southwesterly winds of the atmospheric low, tropical moisture is transported farther northeastward in the early summer, resulting in increased rainfall in the Pacific Northwest region. By elucidating this meridional pathway, our study advances the understanding of ENSO's delayed impacts and associated dynamical processes, in which the midlatitude oceanic feedbacks are emphasized. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) events are considered as a primary driver of climate anomalies. Even during their decaying phase, its impact on the Northern Hemisphere summer climate remains notable. This study delves into the intricate mechanisms underlying the delayed impacts of ENSO events on subsequent summer climates. While prior research has extensively explored the zonal pathways involving tropical Indian and Atlantic oceans, this study illuminates a previously overlooked meridional pathway. It reveals that El Niño events trigger significant cold sea surface temperature anomalies (SSTAs) in the North Pacific during their mature phase in winter, which persist into the following summer. These SSTAs wield substantial influence over early‐summer atmospheric circulation, fostering atmospheric baroclinicity and transient eddy activities. Consequently, an anomalous low‐pressure system emerges over the North Pacific in early summer, enhancing southwesterly winds and transporting tropical moisture farther northeastward. This moisture influx results in increased rainfall in the Pacific Northwest region. By elucidating this meridional pathway, the study advances our comprehension of ENSO's delayed impacts, highlighting the crucial role of midlatitude oceanic feedbacks. In essence, it demonstrates how ENSO events can influence North American climate anomalies during subsequent early summer, shedding light on a previously unrecognized pathway of ENSO's effect. Key Points: Cold central North Pacific sea surface temperature anomalies (SSTAs), initiated by El Niño events, can endure into the subsequent summerBy transient eddy forcing, these cold SSTAs induce a whole‐layer geopotential low anomaly over North Pacific in post‐El Niño early summerThus, northeastward moisture transport strengthens, boosting increased early‐summer rainfall in Pacific Northwest after El Niño events [ABSTRACT FROM AUTHOR]

The stratospheric polar vortex (SPV) significantly influences current weather and climate patterns. However, its state in the geological past remains largely unexplored. This study investigates SPV variations in the past 250 million years, using a fully coupled Earth System Model. It is found that midlatitude paleogeography primarily drove substantial SPV variations in the deep time, while changes in CO2 concentrations and solar insolation play a minor role. Both the Arctic and Antarctic SPV were strengthened when the supercontinent Pangea broke up. The increased asymmetry of midlatitude land‐sea contrast tended to weaken the upward propagation of wavenumber‐1 planetary waves, thereby strengthening the SPV. This SPV strengthening correlated with the decelerated stratospheric Brewer‐Dobson circulation and uplift of the polar tropopause. Our results highlight the crucial role of paleogeography in regulating SPV variations and stratosphere–troposphere coupling in deep‐time climate. Plain Language Summary: At present, influences of the stratospheric polar vortex (SPV) on surface climate have attracted growing attention. In the geological past, however, how the SPV acted and how it impacted on the troposphere and surface climate remains unclear. This study explores SPV variations in both the Northern and Southern Hemispheres in the past 250 million years (Myr) using simulations of a fully coupled Earth System Model. Our results reveal that polar stratospheric temperatures fluctuated by up to 20 K in the geological past, which is much greater than the variations from 1850 to the present. Midlatitude paleogeography played a crucial role in SPV variations over tectonic timescales. The breakup and drift of the Pangea supercontinent altered the upward propagation of Rossby waves from the troposphere into the stratosphere. It influenced not only the SPV but also the strength of stratospheric Brewer‐Dobson circulation as well as the polar tropopause height. This work helps to understand the role of paleogeography in the stratosphere. Key Points: The stratospheric polar vortex (SPV) experienced dramatic variations in the past 250 million yearsMidlatitude paleogeography has a crucial impact on SPV variations by regulating upward propagation of planetary wavesThe SPV variation is closely associated with changes in stratospheric Brewer‐Dobson circulation over tectonic timescales [ABSTRACT FROM AUTHOR]

This study evaluates the capability of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to simulate El Niño‐Southern Oscillation teleconnections in the Southern Hemisphere during austral summer. The wave trains from the tropical Pacific to the Amundsen Sea are underestimated and too far westward in CMIP6 simulations. However, Atmospheric Model Intercomparison Project Phase 6 (AMIP6) experiments well capture the observed location and amplitude of the teleconnection. El Niño and La Niña‐related tropical precipitation anomalies are underestimated in CMIP6 and have their maximum amplitude too far westward, while the precipitation responses in AMIP6 simulations are similar to those observed. The weaker precipitation response in CMIP6 likely arises from a cold bias in climatological‐mean SST, which reduces the sensitivity of precipitation to SST anomalies. Increased resolution in coupled experiments eradicates the westward bias in the El Niño and La Niña‐related circulation anomalies over the Amundsen Sea, but not their insufficient amplitude. Plain Language Summary: Abnormally warm and cold sea surface temperatures (SST) in the tropical Pacific during El Niño and La Niña events, respectively, generate atmospheric circulation anomalies that propagate across the Southern Hemisphere toward the Amundsen Sea, where they influence west Antarctic climate. In this study, we evaluate how well state‐of‐the‐art climate models simulate these El Niño and La Niña‐related teleconnections. We find that free‐running models simulate teleconnections that are too weak and too far westward. When models are provided with realistic SST however, they well simulate the teleconnection location and amplitude. The errors in free‐running models likely occur because the models are too cold in the tropical Pacific, and this reduces the sensitivity of simulated rainfall to SST anomalies; and the SST anomalies are too far westward. Increased ocean resolution eradicates the error in the location of the El Niño and La Niña teleconnections but does not substantially improve their strength. Key Points: CMIP6 models underestimate the intensity of observed ENSO teleconnection to the Amundsen Sea and simulate a westward bias in the wave trainExperiments prescribed with historical global SST and sea ice, closely match the location and strength of observed ENSO‐related wave trainIncreased ocean resolution eliminates the westward bias in the wave train responses to ENSO, but not their insufficient amplitudes [ABSTRACT FROM AUTHOR]

Recent increase in extreme wildfire events has led to major health and environmental consequences across the globe. These adverse impacts underlined the need for better understanding of this phenomenon and to formulate mitigating actions. While previous research has focused on local weather drivers of wildfires, our knowledge about their large‐scale climatic controls remains limited, especially in tropical Africa, which stands out as a global hotspot for fire emissions. Here, we show that interannual variability of carbon emission due to fires in the southern Congo Basin is strongly linked to low‐level winds that are controlled by the Indian Ocean subtropical high. The interhemispheric transport of these emissions to West Africa relies on the intensity and position of both Indian and South Atlantic subtropical highs. Combined effects of this transport mechanism and carbon production in the source region explain a majority of the interannual variability of black carbon in West Africa. Plain Language Summary: Emissions from biomass burning in different parts of the world impact air quality and climatic conditions both locally and in areas distant from the origin. Tropical Africa stands out as a hotspot of fire emissions that are primarily human‐induced. In this study, we show that the year‐to‐year variability of the carbon emission caused by these fires in the southern Congo Basin is directly related to the local winds that are in turn controlled by conditions in the Indian Ocean. Specifically, an intensified subtropical high in the Indian Ocean leads to stronger local winds, exacerbating fire emissions in the Congo Basin. These emissions then traverse the Atlantic Ocean, affecting West Africa—an interhemispheric journey made by the atmospheric circulation patterns. Key Points: Fire emissions in the Congo Basin increase when local winds are strengthened due to intensification of the Indian Ocean subtropical highInterannual variability of black carbon in West Africa is driven by fire emissions in the Congo Basin and winds over the adjacent oceans [ABSTRACT FROM AUTHOR]

Regional hydrological sensitivity (i.e., precipitation change per degree local surface warming) contributes substantially to the uncertainty in future precipitation projections over tropical oceans. Here, we investigate the sensitivity of relative precipitation (P*, precipitation divided by the basin average precipitation) to local sea surface temperature (SST) change by dissecting it into three components, namely the sensitivity of P* to relative SST (SSTrel, SST minus the tropical mean SST) changes, the sensitivity of P* to surface convergence changes, and the sensitivity of surface convergence to SST gradient changes. We show that the relationships between P* and SSTrel, and between P*, surface convergence, and SST gradients are largely constant during climate change. This allows us to constrain regional hydrological sensitivity based on present‐day SST‐precipitation relationships. The sensitivity of surface convergence to SST gradient changes is a main source of uncertainty in regional hydrological sensitivity and is likely underestimated in GCMs. Plain Language Summary: Understanding how precipitation will change over tropical oceans is important because these changes influence the atmospheric circulation, which in turn affects the global climate and weather patterns. Climate models disagree on their projections of precipitation changes over tropical oceans in part due to a lack of understanding on how precipitation should respond to a given amount of local surface warming. We find that the sensitivity of precipitation to future changes in local sea surface temperature (which is commonly referred to as regional hydrological sensitivity) largely depends on the present‐day relationship between precipitation and local sea surface temperature, as well as that between precipitation and the spatial gradient in sea surface temperature, and both relationships are observable and thus can serve as constraints. We find that inter‐model differences in regional hydrological sensitivity result primarily from differences in the response of surface winds to sea surface temperature gradient changes. Key Points: Regional hydrological sensitivity is an important source of uncertainty in rainfall projections over tropical oceansRegional hydrological sensitivity can be constrained by components of rainfall‐temperature relationship that stay constant during warmingUncertainty in regional hydrological sensitivity originates largely from surface convergence sensitivity to temperature gradient changes [ABSTRACT FROM AUTHOR]

In this study, the mechanisms for the long‐lived and medium‐lived regional consecutive cloudy‐rainy events (RCCREs) in the Yangtze‐Huaihe River valley (YHRV) are investigated by comparing the influences of 10–30‐day and 30–90‐day intraseasonal oscillations (ISOs). The evolution of medium‐lived RCCREs is generally dominated by the 10–30‐day ISO, while the 10–30‐day and 30–90‐day ISOs synergistically contribute to the occurrence of long‐lived RCCREs. Further analysis reveals that, when the East Asian westerly jet (EAWJ) shifts northward to the north of YHRV, a RCCRE in the YHRV occurs in 2 days later. In the medium‐lived RCCREs, the EAWJ retreats southward rapidly; while in the long‐lived RCCREs, the stronger 30–90‐day ISO prevents the southward retreat of EAWJ, which favors the persistence of the RCCREs in the YHRV. The northward shifted EAWJ facilitates the RCCREs by modulating the secondary atmospheric circulation, consequently enhancing the moisture convergence and ascending motion anomalies over the YHRV. The RCCREs‐related precursor wave train originates from northern Europe with at least a 4‐day lead. The wave train propagates southeastward to excite an anomalous high over East Asia, which contributes to the northward shift of EAWJ and subsequently the occurrence of RCCREs. Different from the rapid weakness of the precursor wave train associated with the medium‐lived RCCREs, the precursor wave train associated with the long‐lived RCCREs can be maintained by the 30–90‐day ISO, which consequently leads to a persistence of the northward located EAWJ and long‐lived RCCREs in the YHRV. Plain Language Summary: Regional consecutive cloudy‐rainy events (RCCREs) have a disastrous impact on economy, agriculture, and natural environment over the Yangtze‐Huaihe River valley (YHRV). This study investigates the mechanisms contributing to the long‐ and medium‐lived RCCREs in the YHRV by comparing the role of 10–30‐day and 30–90‐day intraseasonal oscillations (ISOs). The medium‐lived RCCREs are dominated by the 10–30‐day ISO, while the long‐lived RCCREs are caused by a combination of the 10–30‐day and 30–90‐day ISOs. The East Asian westerly jet (EAWJ) plays a crucial role in RCCRE occurrence. When the EAWJ shifts northward, it triggers RCCREs by enhancing moisture convergence and ascending motion over the YHRV. The EAWJ retreats southward rapidly in the medium‐lived RCCREs. Conversely, the stronger 30–90‐day ISO prevents its southward retreat in the long‐lived RCCREs, favoring the persistence of RCCRE in the YHRV. Additionally, the precursor wave train originating from northern Europe contributes to the northward shift of the EAWJ and the occurrence of the RCCREs over the YHRV. Although both the long‐ and medium‐lived RCCREs exhibit similar precursor wave train, the influence of different ISOs varies, with the 30–90‐day ISO showing a larger impact on the precursor wave train and northward shift of the EAWJ in the long‐lived RCCREs. Key Points: Medium (long)‐lived RCCREs are mainly influenced by 10–30‐day intraseasonal oscillation (ISO) (both 10–30‐day and 30–90‐day ISOs)In the long (medium)‐lived RCCREs, the East Asian westerly jet (EAWJ) remains stable (retreats southward rapidly) after shifting northwardThe precursor wave train of the medium‐lived RCCREs weakens rapidly, while that of the long‐lived RCCREs is maintained by 30–90‐day ISO [ABSTRACT FROM AUTHOR]

Decadal variations in near‐surface wind speed (NSWS) and their causes are poorly understood. We found that the decadal transition of winter NSWS in northern China (NC) was 10 years earlier than in southern China (SC), which could be linked to the changes in intensities of the eastward wave‐activity flux and Siberian High (SH) induced by the Warm Arctic‐Cold Eurasia (WACE) dipole pattern. From 1973 to 1990, the WACE pattern from positive to negative phases confined the eastward wave trains to high latitudes with a decreasing SH, inducing an NSWS reduction. From 1991 to 2000, the WACE strengthened from negative to positive phases, causing a decadal transition in NSWS first in NC. After 2000, accompanied by the strengthening of the positive WACE, the eastward wave trains propagated downstream to lower latitudes, the SH and the meridional pressure gradient enhanced. Therefore, the transition of decadal NSWS occurred in SC until 2000. Plain Language Summary: Near‐surface wind speed (NSWS) is critical in exchanging energy, water, and momentum between the Earth's surface and the lower atmosphere. Previous studies have reported that the slowdown in NSWS and its reversal could be a manifestation of decadal variations in the climate system. However, the regional non‐synchronization of decadal variations in NSWS and the corresponding cause are poorly understood. This study reported a non‐synchronization of the decadal transition in winter NSWS between northern China (NC) and southern China (SC). The significant turning point of winter NSWS across NC was 10 years earlier than those across SC, and it was caused mainly by the zonal wind. The non‐synchronization of decadal variations in winter NSWS between NC and SC was linked to the Warm Arctic‐Cold Eurasia (WACE) atmospheric circulation pattern, and the Siberian High (SH) could serve as a bridge through which the WACE atmospheric circulation pattern influences the asynchronous transition of decadal NSWS between NC and SC. This study improves the understanding of decadal variations in NSWS across China. Key Points: The decadal near‐surface wind speed (NSWS) transition in winter over northern China (NC) was 10 years earlier than in southern China (SC)The non‐synchronization of the decadal transition in NSWS between NC and SC was linked with the Warm Arctic‐Cold Eurasia patternIntensities of wave‐activity flux and Siberian High influenced the non‐synchronization of decadal transition in NSWS between NC and SC [ABSTRACT FROM AUTHOR]