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The heat transfer from the low latitudes to high latitudes is responsible for maintaining the earth's climate dynamics. Thus, deciphering the possible mechanism driving the variability of the Indian summer monsoon (ISM) during the Holocene Epoch has been critical to understand the hydroclimatic changes of the low latitudes. Despite several efforts, the teleconnection of ISM with the global climate dynamics remains under-represented and poorly understood. The present study aims to delineate the ISM variability and its possible forcing mechanism from western India (Gujarat). In this study, a sediment core (~65 cm long) was raised from the Jaffrabad mudflat (MIT) in western Gujarat. The sediment samples were subjected to geochemical analysis to investigate paleomonsoon, paleo-sediment source and paleoweathering changes. The results show that, with the addition of intermediate sources, the sediments were principally derived from the hinterland's Deccan basalts. Further, the study suggested a warm and wet climate due to strong ISM during 10,650−5500 cal yr BP associated with the solar as well as orbital forcings. The weak monsoon during 5500−2700 cal yr BP has been linked with southward migration of the Intertropical Convergence Zone (ITCZ) along with the increased El Niño-like conditions. Further, the wavelet analysis revealed that a combined influence of solar, orbital and North Atlantic forcings led to monsoon variability along western India, during the Holocene Epoch. By reconciling the geochemical proxies, the present study has implications in the reconstruction of paleomonsoon and establishing the possible teleconnection with the global climate system. [ABSTRACT FROM AUTHOR]

The likely changes to precipitation seasonality with warming are both impactful and not well understood. This work aims to describe areas that experience similar changes to seasonal precipitation irrespective of the original underlying precipitation seasonality. We train a self-organizing map on the difference between the seasonal cycle of precipitation in the past and in a high-warming future climate as represented by the Community Earth System Model, version 2, to create regions with similar changes in precipitation seasonality. This method is applied separately over land and ocean surfaces because of the differing processes leading to precipitation over each. This method indicates that future changes in seasonal precipitation are most varied in the tropics because of a southward shift in the intertropical convergence zone. The seasonal shifts found over midlatitude oceans indicate a poleward shift in atmospheric river activity. We find a correspondence between certain land-based precipitation changes and Köppen climate classification. The seasonality of large-scale and convective precipitation is examined for each region. The relationship between the seasonal changes to precipitation and associated atmospheric processes is discussed. These processes include atmospheric rivers, the intertropical convergence zone, tropical cyclones, and monsoons. [ABSTRACT FROM AUTHOR]

The Intertropical Convergence Zone (ITCZ) is a narrow tropical belt of deep convective clouds, intense precipitation, and monsoon circulations encircling the Earth. Complex interactions between the ITCZ and local geophysical dynamics result in high climate variability, making weather forecasting and prediction of extreme rainfall or drought events challenging. We unravel the complex spatio-temporal dynamics of the ITCZ and the resulting teleconnection patterns via a novel tropical climate classification achieved using complex network analysis and community detection. We reduce the high-dimensional complex ITCZ dynamics into a simple yet insightful community structure that classifies the tropics into seven regions representing distinct ITCZ dynamics. The two largest communities, encompassing landmasses over the Northern and Southern hemispheres, are associated with coherent seasonal ITCZ dynamics and have significant long-range connections. Temporal analysis of the community structure highlights that the tropical Pacific and Atlantic Oceans communities exhibit substantial variation on multidecadal scales. Further, these communities exhibit incoherent dynamics due to atmosphere-ocean interactions driven by equatorial and coastal oceanic upwelling. [ABSTRACT FROM AUTHOR]

The equatorward contraction of tropical precipitation, commonly referred to as the "deep‐tropical contraction", is witnessed in the paleoclimate simulations of the early Eocene. However, the mechanism driving this contraction is still unclear. Based on the energetics framework of the Intertropical Convergence Zone (ITCZ) and the decomposition method of the latent heat flux along with the simulations of a climate system model, CESM1.2, we proposed a novel mechanism responsible for the "deep‐tropical contraction" in the early Eocene. The greenhouse gases‐induced sea surface warming amplifies the sensitivity of evaporation to surface wind speed changes through Clausius‐Clapeyron scaling, leading to an interhemispheric asymmetric enhancement of the latent heat flux. To maintain hemispheric energy balance, the cross‐equatorial atmospheric energy transport must be reduced during the solstice seasons. As a result, the solstitial location of the ITCZ shifts equatorward, causing the "deep‐tropical contraction" in the early Eocene. Plain Language Summary: The early Eocene is the warmest epoch in the last 65 million years, with a global mean temperature 9°C–23°C higher than the preindustrial period. According to state‐of‐the‐art climate models, the tropical rainfall contracted toward the equator during this extremely warm period. However, the physical mechanism causing this phenomenon remains unclear. In this study, we examined the hemispheric energy balance in the early Eocene that causes the equatorward contraction of tropical precipitation. A novel mechanism underlying this phenomenon is revealed. Based on the climate modeling of CESM1.2, we show that the GHG‐induced warmth enhances the sensitivity of evaporation to surface wind speed changes in the early Eocene. Thus, the stronger tropical trade wind in the winter hemisphere will drive out stronger latent heat flux than in the summer hemisphere. This interhemispheric asymmetric response reduces the interhemispheric heating contrast in the solstice seasons. As a result, the ascending motion in the tropical atmosphere migrates toward the equator, finally decreases the width of tropical precipitation in the early Eocene. Key Points: The "deep tropical contraction" in the early Eocene is caused by the equatorward migration of the seasonal ITCZThe equatorward migration of the solstitial ITCZ location in the early Eocene is due to decreased cross‐equatorial energy transportThe enhanced wind‐evaporation effect in the early Eocene reduces the cross‐equatorial atmospheric energy transport in the solstitial seasons [ABSTRACT FROM AUTHOR]

In this study, we aim to reconstruct southern India's intrinsic environmental changes over the past 1500 years from 3330 to 1830 cal BP by investigating the sedimentation and weathering dynamics in Lake Shantisagara, one of Karnataka's largest lakes. Four distinct climatic phases were delineated based on sedimentological, geochemical, and End Member Modelling Analysis (EMMA) results. Phase 1 (3330-3100 cal BP) is a short-term low rainfall zone characterized by a calm hydrodynamic environment and weak chemical weathering. Phase 2 (3100-2800 cal BP) is a climatically unstable phase, fluctuating between low and high rainfall conditions. Phase 3 (2800-2200 cal BP) is characterized by a stable, low rainfall climate with weak fluvial activity and chemical weathering. It is followed by a highly unstable phase marked by frequent extreme climatic events (Phase 4; 2200-1830 cal BP). Our study reveals a highly unstable hydrodynamic condition that culminated in potentially catastrophic high rainfall events that triggered intense and frequent floods in southern India around ∼2208, 2054, 1958, and 1891 cal BP. Comparative studies of regional records show that the regional climate pattern is similar. There is a strong effect of Total Solar Irradiance (TSI), Sea Surface Temperature (SST) off the Malabar coast, location of the Intertropical Convergence Zone (ITCZ), and the El Niño Southern Oscillation (ENSO) on the monsoon system in southern India. This suggests that there is a global teleconnection. [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) are crucial in shaping large‐scale tropical circulation and the hydrological cycle, particularly in Northwestern South America (NwSA), a region marked by complex terrain and significant MCS activity. Understanding MCSs in NwSA is vital due to their impact on precipitation patterns and potential for severe weather events. To enhance this understanding, the ATRACKCS algorithm was developed for tracking convective systems, utilizing precipitation and brightness temperature data sets. This research focuses on documenting the spatiotemporal variability of MCS occurrence, life cycle, and movement. Notably, MCS hotspots were identified to the west of the major orographic features in the region, with maximum occurrences at night, contrasting with the region's typical afternoon peak in land convection. MCS movement is also heavily influenced by topography, with higher velocities on the eastern (windward) side of the Andes compared to velocities on the western (leeward) side. MCSs generally move westward, driven by easterly winds, but this pattern is not consistent throughout the year or region. Northward movement is predominant to the west of the Andes, while southward movement is observed to the east. These seasonal and regional movement variations are linked to factors such as the intertropical convergence zone position, moisture availability, topography, and low‐level jets. This research underscores the complexity of MCSs in NwSA and emphasizes the need for detailed studies on the atmospheric environment shaping these systems. Additionally, it provides a robust 21‐year MCS database for NwSA and an advanced tracking tool for research in various geographic contexts and impact areas. Plain Language Summary: Extreme storms are linked to large clusters of clouds called Mesoscale Convective Systems (MCSs). Understanding MCSs is important because they produce rainfall and severe weather. Northwestern South America (NwSA) has many MCSs but studying them is difficult due to complex terrain and limited radar data. Here, we developed a new algorithm (ATRACKCS) to study MCSs over NwSA using satellite data, including their occurrence, duration, and movement. Topography has a strong effect on MCS. They occur more on the west side of the Andes mountain but are faster on the east side than to the west. Also, MCSs tend to move westward and are affected by winds, but this movement varies throughout the year and region. This variability could be explained by moisture availability, low‐level jets, and topography. This research shows how complex MCSs are in NwSA and highlights the need for detailed studies on the environmental conditions affecting them. It also helps us to better understand these storms by providing a robust database and a valuable tool for studying them in other places worldwide. Key Points: A climatological analysis of mesoscale convective system (MCS) characteristics as occurrence, life cycle and propagation are presented for Northwestern South AmericaContinental MCS hotspots are predominantly nocturnal and located west of topographic featuresMCS move mostly westward. However, their movement doesn't align with ambient winds at certain locations and times of the year [ABSTRACT FROM AUTHOR]

The North Pacific Oscillation (NPO) is an important intrinsic atmospheric pattern over the North Pacific. Observations have shown that the boreal winter NPO is a crucial precursor to the El Niño-Southern Oscillation (ENSO), with many ENSO events being preceded by the NPO. It is therefore imperative to assess the ability of current coupled climate models to reproduce the relationship between winter NPO and the subsequent winter ENSO. Previous studies have shown that most coupled climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) underestimate the influence of winter NPO on the subsequent winter ENSO. Simulations from CMIP6, representing the latest generation of climate models, are now available. This study shows a remarkable improvement of the CMIP6 models in simulating the influence of winter NPO on the subsequent ENSO development compared to the CMIP5 models. This improvement is due to the improved air-sea interaction over the subtropical North Pacific in CMIP6. The enhanced air-sea interaction over the subtropical North Pacific promotes the equatorward propagation of the NPO-induced wind and SST anomalies, resulting in enhanced surface zonal wind anomalies over the tropical western Pacific, which further exert a stronger influence on the subsequent winter ENSO development by triggering the tropical Bjerknes positive air-sea interaction. The enhanced subtropical air-sea interaction is thought to be related to a southward shift of the North Pacific intertropical convergence zone in CMIP6 compared to CMIP5. [ABSTRACT FROM AUTHOR]

Hydroclimate variation and vegetation changes of the Nile River watershed area in northeast Africa since the Last Glacial Maximum (LGM) were reconstructed based on n‐alkanes, their carbon isotope ratios (δ13Cn‐alkanes), and their hydrogen isotope ratios (δ2Hn‐alkanes) in sediments from ODP Site 967 in the Eastern Mediterranean Sea. The results were compared with the present vegetation cover in the watershed areas using ArcGIS. The average proportion of current grassland in the Equatorial Lake and Ethiopian Highland Plateaus watershed areas was 45.8 and 64.7%, respectively. δ2Hn‐alkanes ranged from −199 to −127‰ and co‐varied with insolation change response to orbital forcing. Depleted δ2Hn‐alkanes were found from deglaciation to the middle Holocene, suggesting increased precipitation during the African Humid Period (AHP) from 15 to 5 ka caused by northward migration of the Intertropical Convergence Zone. However, lower precipitation was inferred by enriched δ2Hn‐alkanes during the LGM and late Holocene. δ13Cn‐alkanes at Site 967 did not show a trend in harmony with δ2Hn‐alkanes and instead exhibited millennial‐scale variations ranging from –25.9 to –33.2‰. These δ13Cn‐alkanes values consistently indicated a C4 grass‐dominated environment in the watershed areas of the River Nile since the LGM, persisting through the AHP and into the present. Reconstructions demonstrated orbital and abrupt forcing of hydroclimate variability while maintaining generally grass‐dominated vegetation with weak precipitation feedback over the late Quaternary. [ABSTRACT FROM AUTHOR]

The South American summer monsoon (SASM) profoundly influences tropical South America's climate, yet understanding its low-frequency variability has been challenging. Climate models and oxygen isotope data have been used to examine the SASM variability over the last millennium (LM) but have, at times, provided conflicting findings, especially regarding its mean-state change from the Medieval Climate Anomaly to the Little Ice Age. Here, we use a paleoclimate data assimilation (DA) method, combining model results and δ18O observations, to produce a δ18O-enabled, dynamically coherent, and spatiotemporally complete austral summer hydroclimate reconstruction over the LM for tropical South America at 5-year resolution. This reconstruction aligns with independent hydroclimate and δ18O records withheld from the DA, revealing a centennial-scale SASM intensification during the MCA-LIA transition period, associated with the southward shift of the Atlantic Intertropical Convergence Zone and the strengthening Pacific Walker circulation (PWC). This highlights the necessity of accurately representing the PWC in climate models to predict future SASM changes. [ABSTRACT FROM AUTHOR]

Reducing uncertainty in the response of the Amazon rainforest, a vital component of the Earth system, to future climate change is crucial for refining climate projections. Here we demonstrate an emergent constraint (EC) on the future response of the Amazon carbon cycle to climate change across CMIP6 Earth system models. Models that overestimate past global warming trends, tend to estimate hotter and drier future Amazon conditions, driven by northward shifts of the intertropical convergence zone over the Atlantic Ocean, causing greater Amazon carbon loss. The proposed EC changes the mean CMIP6 Amazon climate-induced carbon loss estimate (excluding CO2 fertilisation and land-use change impacts) from −0.27 (−0.59–0.05) to −0.16 (−0.42–0.10) GtC year−1 at 4.4 °C warming level, reducing the variance by 34%. This study implies that climate-induced carbon loss in the Amazon rainforest by 2100 is less than thought and that past global temperature trends can be used to refine regional carbon cycle projections. A study shows an emergent constraint on the Amazon carbon cycle response to climate change. The CMIP6 ESMs that overestimate past global temperature trends, tend to project hotter, drier conditions and greater climate-induced Amazon carbon source. [ABSTRACT FROM AUTHOR]

Wildfires and agricultural burning generate seemingly increasing smoke aerosol emissions, impacting societal and natural ecosystems. To understand smoke's effects on climate and public health, we analyzed the spatiotemporal distribution of smoke aerosols, focusing on two major light-absorbing components, namely black carbon (BC) and brown carbon (BrC) aerosols. Using NASA's Earth Polychromatic Imaging Camera (EPIC) instrument aboard NOAA's Deep Space Climate Observatory (DSCOVR) spacecraft, we inferred BC and BrC volume fractions and particle mass concentrations based on spectral absorption provided by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm with 1–2 h temporal resolution and ∼ 10 km spatial resolution over North America and central Africa. Our analyses of regional smoke properties reveal distinct characteristics for aerosol optical depth (AOD) at 443 nm, spectral single-scattering albedo (SSA), aerosol layer height (ALH), and BC and BrC amounts. Smoke aerosols in North America showed extremely high AOD up to 6, with elevated ALH (6–7 km) and significant BrC components up to 250 mg m -2 along the transport paths, whereas the smoke aerosols in central Africa exhibited stronger light absorption (i.e., lower SSA) and lower AOD, resulting in higher-BC mass concentrations and similar BrC mass concentrations than the cases in North America. Seasonal burning source locations in central Africa, following the seasonal shift in the Intertropical Convergence Zone and diurnal variations in smoke amounts, were also captured. A comparison of retrieved AOD 443 , SSA 443 , SSA 680 , and ALH with collocated AERONET and CALIOP measurements shows agreement with RMSE values of 0.2, 0.03–0.04, 0.02–0.04, and 0.8–1.3 km, respectively. An analysis of the spatiotemporal average reveals distinct geographical characteristics in smoke properties closely linked to burning types and meteorological conditions. Forest wildfires over western North America generated smoke with a small-BC volume fraction of 0.011 and a high ALH with large variability (2.2 ± 1.2 km), whereas smoke from wildfires and agricultural burning over Mexico region shows more absorption and low ALH. Smoke from savanna fires over central Africa had the most absorption, with a high-BC volume fraction (0.015) and low ALH with a small variation (1.8 ± 0.6 km) among the analyzed regions. Tropical forest smoke was less absorbing and had a high variance in ALH. We also quantify the estimation uncertainties related to the assumptions of BC and BrC refractive indices. The MAIAC EPIC smoke properties with BC and BrC volume and mass fractions and assessment of the layer height provide observational constraints for radiative forcing modeling and air quality and health studies. [ABSTRACT FROM AUTHOR]

The Atmospheric Dynamics Mission ADM-Aeolus was successfully launched in August 2018 by the European Space Agency (ESA). The Aeolus mission carried a single instrument, the first-ever Doppler wind lidar (DWL) in space, called Atmospheric LAser Doppler INstrument (ALADIN). Aeolus circled the Earth, providing vertical profiles of horizontal line-of-sight (HLOS) winds on a global scale. The Aeolus satellite's measurements filled critical gaps in existing wind observations, particularly in remote regions such as the Brazilian Amazon. This area, characterized by dense rainforests and rich biodiversity, is essential for global climate dynamics. The weather patterns of the Amazon are influenced by atmospheric circulation driven by Hadley cells and the Intertropical Convergence Zone (ITCZ), which are crucial for the distribution of moisture and heat from the equator to the subtropics. The data provided by Aeolus can significantly enhance our understanding of these complex atmospheric processes. In this long-term validation study, we used radiosonde data collected from three stations in the Brazilian Amazon (Cruzeiro do Sul, Porto Velho, and Rio Branco) as a reference to assess the accuracy of the Level 2B (L2B) Rayleigh-clear and Mie-cloudy wind products. Statistical validation was conducted by comparing Aeolus L2B wind products and radiosonde data covering the period from October 2018 to March 2023 for Cruzeiro do Sul and Porto Velho, and from October 2018 to December 2022 for Rio Branco. Considering all available collocated winds, including all stations, a Pearson's coefficient (r) of 0.73 was observed in Rayleigh-clear and 0.85 in Mie-cloudy wind products, revealing a strong correlation between Aeolus and radiosonde winds, suggesting that Aeolus wind products are reliable for capturing wind profiles in the studied region. The observed biases were −0.14 m/s for Rayleigh-clear and −0.40 m/s for Mie-cloudy, fulfilling the mission requirement of having absolute biases below 0.7 m/s. However, when analyzed annually, in 2022, the bias for Rayleigh-clear was −0.95 m/s, which did not meet the mission requirements. [ABSTRACT FROM AUTHOR]

The present study analyzes zonal mean cloud and radiation trends over the global oceans for the past 35 years from a suite of satellite datasets covering two periods. In the longer period (1984–2018) cloud properties come from the ISCCP-H, CLARA-A3, and PATMOS-x datasets and radiative properties from the ISCCP-FH dataset, while for the shorter period (2000–2018) cloud data from MODIS and CloudSat/CALIPSO and radiative fluxes from CERES-EBAF are added. Zonal mean total cloud cover (TCC) trend plots show an expansion of the subtropical dry zone, a poleward displacement of the midlatitude storm zone and a narrowing of the tropical intertropical convergence zone (ITCZ) region over the 1984–2018 period. This expansion of the 'low cloud cover curtain' and the contraction of the ITCZ rearrange the boundaries and extents of all major climate zones, producing a more poleward and narrower midlatitude storm zone and a wider subtropical zone. Zonal mean oceanic cloud cover trends are examined for three latitude zones, two poleward of 50 ° and one bounded within 50oS and 50oN, and show upward or near-zero cloud cover trends in the high latitude zones and consistent downward trends in the low latitude zone. The latter dominate in the global average resulting in TCC decreases that range from 0.72% per decade to 0.17% per decade depending on dataset and period. These contrasting cloud cover changes between the high and low latitude zones produce contrasting low latitude cloud radiative warming and high latitude cloud radiative cooling effects, present in both the ISCCP-FH and CERES-EBAF datasets. The global ocean mean trend of the short wave cloud radiative effect (SWCRE) depends on the balance between these contrasting trends, which in the CERES dataset materializes as a SW cloud radiative warming trend of 0.12 W/m2/decade coming from the dominance of the low-latitude positive SWCRE trends while in the ISCCP-FH dataset it manifests as a 0.3 W/m2/decade SW cloud radiative cooling trend coming from the dominance of the high latitude negative SWCRE trends. The CERES cloud radiative warming trend doubles in magnitude to 0.24 W/m2/decade when the period is extended from 2016 to 2022, implying a strong cloud radiative heating in the past 6 years coming from the low latitude zone. [ABSTRACT FROM AUTHOR]

Wind gustiness is an effective approach for addressing mesoscale enhancement in estimating air-sea interface fluxes. In this study, an improved convective gustiness parameterization scheme based on convective available potential energy (CAPE) is formulated utilizing reanalysis data and wind observations from moored buoys. This new parameterization was examined by implementing it in the air-sea flux transfer scheme within the National Center for Atmospheric Research Community Earth System Model (NCAR CESM) version 2.1.3 and contrasting it with a previously proposed scheme based on convective precipitation rate. The results indicate a significant reduction in negative biases of surface winds and latent heat fluxes over the tropical Indian Ocean and western Pacific during summer with the implementation of either gustiness scheme, resulting in an average increase in latent heat flux of approximately 9 W·m− 2. Specifically, the CAPE-based scheme shows a more favorable impact in the Indo-Pacific Warm Pool region, whereas the precipitation-based scheme exhibits inferior performance in the western Pacific Intertropical Convergence Zone. Further analysis reveals that the inclusion of the gustiness scheme distinctly alters surface evaporation and latent heat flux, influencing vertical motion in the area with active convective activity and effectively improving precipitation simulations by up to 18%. Moreover, the CAPE-based scheme reduces the bias in summer precipitation simulations by approximately 5% more than the precipitation-based scheme. [ABSTRACT FROM AUTHOR]

In this study, we analyse the large-scale biases in tropical precipitation climatology of two different types of coupled ocean–atmosphere general circulation models (GCMs): the coupled model intercomparison project (CMIP) models and ICON-Sapphire, a global storm-resolving model. We employ the simple globally resolved energy balance (GREB) diagnostic precipitation model to evaluate four drivers of the precipitation biases in the simulations: surface specific humidity, surface relative humidity, tropospheric mean and variability in the vertical motion. The tropical precipitation biases in the CMIP and ICON-Sapphire simulations are surprisingly similar in their patterns and also in the elements forcing them. The results of our analysis using the GREB model show that the precipitation biases result from both biases in the sensitivity to the four forcing fields and biases in the simulated forcing fields themselves. The most significant bias for both, the CMIP and ICON-Sapphire simulations, is a too high sensitivity to the mean vertical circulation ( ω mean ) and bias in the ω mean climatology itself. This also holds for specific long-standing biases, such as the double intertropical convergence zone problem. Meanwhile, biases in the climatology of specific and relative humidity play only a minor role but contribute to an overall small increase in precipitation in CMIP models that may be related to the "drizzling" bias. These results can give insights to the modelling community regarding model development, and illustrate that the GREB diagnostic precipitation model applied is a good tool for evaluating the drivers of large-scale tropical precipitation. [ABSTRACT FROM AUTHOR]

This study analyzes the atmospheric and oceanic mechanisms that influenced rainfall distribution in Ceará, Brazil during the 2018 rainy season and the impacts of the observed rainfall distribution on agriculture in the region. Special attention is given to the month of March, when precipitation was below the climatological average. Precipitation, wind, omega, specific humidity, outgoing longwave radiation, and oceanic indices from the Pacific and Atlantic data were used in the analyses. The Multivariate Real-Time Madden–Julian Oscillation (MJO) Index was employed to assess the influence of the MJO on precipitation in March 2018. The results indicate that subseasonal variability, through the MJO in phases 4, 5, and 6, played a crucial role in suppressing convective activity. Additionally, a delayed austral summer pattern was found, with the South American Convergence Zone (SACZ) positioned further north and a quasi-stationary trough at altitude. These two atmospheric factors inhibited the more intense rainfall activity in the Intertropical Convergence Zone (ITCZ). In the ocean analyses, Sea Surface Temperature (SST) anomalies indicated the presence of La Niña in the equatorial Pacific, although it was in transition from cooling to warming. This, in addition to the neutrality of the interhemispheric gradient of the Tropical Atlantic SST anomalies, may have also contributed to negative precipitation anomalies and influenced the MJO displacement. MJO phases associated with suppression contributed to economic losses for the agricultural sector. [ABSTRACT FROM AUTHOR]

Abstract The mid-Brunhes dissolution interval (MBDI; Marine Isotope Stage (MIS) 13 to 7; ~ 533–191 ka) is characterized by various paleoclimatic/paleoceanographic events in the world. We investigated fossil deep-sea benthic foraminifera and sediment geochemistry at the onset of the MBDI (~ 670–440 ka) using Ocean Drilling Program (ODP) Site 758 and core GPC03 in the northeast tropical Indian Ocean (TIO), primarily focusing on the relationship between the paleoceanographic conditions of the surface and deep oceans. Based on multi-dimensional scaling, MDS axis 1 is related to the specific depth habitats of benthic foraminiferal fauna, possibly at the trophic level. In MDS axis 1, the difference between the two core sites was smaller from ~ 610 to 560 ka, whereas it was larger from ~ 560 to 480 ka. In contrast, MDS axis 2 may be related to the low food supply at episodic food pulses/relatively stable and low food fluxes. MDS axis 2 showed generally similar stratigraphic variations between the two cores during ~ 610–560 ka, but was different during ~ 560–480 ka. The proportion of lithogenic matter to biogenic carbonate was relatively low from ~ 610 to 530 ka under the highstand when sediment transport to the study area was reduced. Thus, both the depth gradient in the distribution of benthic foraminiferal fauna and the lithogenic supply between the two cores changed coincidently across the MIS 15/14 (~ 570–540 ka) transition. Such paleoceanographic conditions across MIS 15/14 transition were attributed to the long-term weakening of the wind-driven mixing of surface waters, which might have been caused by the weakening of the Indian summer monsoon in the northeast TIO, possibly with the northward displacement of the InterTropical Convergence Zone in the Northern Hemisphere. In particular, the depth gradient in the distributions of benthic foraminiferal faunas represents the paleoceanographic linkage between the surface and deep oceans through particulate organic matter ballasting by calcareous plankton skeletons in addition to lithogenic matter, which changed transiently and significantly across MIS 15/14 transition close to the onset of the MBDI.

The doldrums are regions of low wind speeds and variable wind directions in the deep tropics that have been known for centuries. Although the doldrums are often associated with the Intertropical Convergence Zone (ITCZ), the exact relationship remains unclear. This study re‐examines the relationship between low‐level convergence and the Atlantic doldrums. By analyzing the frequency distribution of low wind speed events in reanalysis and buoy data, we show that the doldrums are largely confined between the edges of the ITCZ marked by enhanced surface convergence. While the region between the edges is a region of high time‐mean precipitation, low wind speed events occur in the absence of precipitation. Based on these results, we hypothesize that low wind speed events occur in regions of low level divergence rather than convergence. Plain Language Summary: The doldrums, an area between the trade winds formerly feared by mariners because of its low wind speeds and variable wind directions, have largely disappeared from mention in the scientific literature. The most commonly given explanation for the existence of the doldrums, according to which the weaker surface winds result from the upward circulation of the trade winds, can only be true when averaged over timescales of days or weeks. In this study, we re‐examine this region and its relationship to the convergence of the trade winds. We show that although low wind speed events occur in the region where the trade winds meet and precipitation rates are high on average, they occur precisely when there is no precipitation. This leads us to the hypothesis that these regions of low wind speeds are characterized by sinking rather than rising air. Key Points: The doldrums are confined to the area of time‐mean convergence of the Atlantic Intertropical Convergence Zone (ITCZ)The frequency distribution of low wind speed events peaks between the edges of the ITCZ, which are characterized by increased convergenceLow wind speed events within the ITCZ occur when precipitation is absent, suggesting they coincide with local low‐level divergence [ABSTRACT FROM AUTHOR]

The North Pacific Meridional Mode (PMM) is the strongest interannual air‐sea coupled system in the subtropical northeastern Pacific, which can significantly impact the development of El Niño and Southern Oscillation (ENSO). This study examines performance of the second version of the Chinese Academy of Sciences Earth System Model (CAS‐ESM2), developed primarily at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP/CAS), in simulating the PMM, ENSO, and their relationship. It reveals that CAS‐ESM2 can well reproduce the tropical climate mean states, including sea surface temperature (SST), surface winds, and precipitation. Furthermore, the model shows a good ability in reproducing the seasonal evolutions of the PMM and ENSO. Moreover, CAS‐ESM2 effectively simulates the influence of the PMM on subsequent ENSO and the underlying physical mechanisms, including the wind‐evaporation‐SST feedback process, the trade wind charging mechanism and summer deep convection mechanism. However, some improvements are still needed, particularly in representing the periodicity of the PMM, an overestimation of the ENSO intensity and westward extension of ENSO‐related SST anomalies in the tropical Pacific. The results obtained from the CAS‐ESM2 showcase significant progress in understanding the interaction between air‐sea interaction systems over the tropics and subtropics. Plain Language Summary: El Niño and Southern Oscillation (ENSO) is the strongest interannual atmosphere‐ocean coupling variability in the tropical Pacific. ENSO can trigger extreme weather and climate events worldwide, and lead to substantial economic losses. While tropical processes are acknowledged to influence ENSO, many recent studies have emphasized the important role of extratropical air‐sea variabilities in modulating the occurrence and development of ENSO events. The Pacific Meridional Mode (PMM) has been identified as a key channel in transmitting the impact of extratropical forcing on ENSO. Therefore, it is crucial to evaluate the performance of current climate models in representing the PMM and its relationship with the ENSO. This evaluation holds significant scientific value as it can enhance our understanding of the dynamics underlying the ENSO and help improve the prediction of ENSO. The second version of the Chinese Academy of Sciences Earth System Model (CAS‐ESM2), developed primarily at the Institute of Atmospheric Physics, Chinese Academy of Sciences, represents a significant milestone in advancing atmospheric science in China. This study aims to assess the capabilities of CAS‐ESM2 in simulating the ENSO, PMM, and the impact of PMM on ENSO. Our findings indicate that CAS‐ESM2 well reproduces these two air‐sea coupling systems and captures their relation. Key Points: Chinese Academy of Sciences Earth System Model (CAS‐ESM2) has eliminated the double Intertropical Convergence Zone bias to some extentCAS‐ESM2 can reasonably well simulate the spatial‐temporal features of Pacific Meridional Mode (PMM) and El Niño and Southern Oscillation (ENSO)The influence of the spring PMM on ENSO and the underlying mechanism can be captured by the CAS‐ESM2 [ABSTRACT FROM AUTHOR]

We investigate the position and intensity changes of the Intertropical Convergence Zone (ITCZ) over Asia (50°E−135°E) relative to the preindustrial period annually and seasonally during the Last Interglacial (LIG), Last Glacial Maximum (LGM), and mid‐Holocene (MH) using available models from phases 3 and 4 of the Paleoclimate Modeling Intercomparison Project. The multi‐model mean shows that the June–July–August ITCZ variations generally dominate the annual changes. The Asian ITCZ shifts northward over western Asia and southward over the eastern side in both the LIG and MH, and the opposite occurs in the LGM. Its intensity varies with longitude similarly for the LIG and MH and generally weakens in the LGM. Precipitation changes associated directly with ITCZ indices are primarily caused by the dynamic term in the LIG and MH, while both dynamic and thermodynamic terms play roles in the LGM, with major contributions from the convergence components. Plain Language Summary: As an intense rain belt, the Intertropical Convergence Zone (ITCZ) has an important influence on the regional climate, particularly over Asia. However, its future and past behaviors remain unclear. Based on multi‐model experiments, we investigate Asian ITCZ changes in location and intensity during the past three typical periods: the interglacial periods of the Last Interglacial and the mid‐Holocene and the glacial period of the Last Glacial Maximum. The Asian ITCZ overall strengthens and regionally moves northward over the western part and southward over the eastern part during the two interglacial periods relative to its preindustrial state, which are generally opposite to the position and intensity changes in the glacial period. These ITCZ changes are directly caused by uneven precipitation changes, which are dominated by atmospheric circulation changes during interglacial periods and additionally contributed from water vapor content changes during glacial periods, primarily through the vertical motion of air. Key Points: Asian Intertropical Convergence Zone (ITCZ) shifts northward over western Asia and southward over the eastern side in Last Interglacial (LIG) and mid‐Holocene (MH), and the opposite occurs in Last Glacial Maximum (LGM)Asian ITCZ intensity varies with longitude similarly for LIG and MH, while it weakens during LGMDynamic term dominates the ITCZ‐related precipitation changes in LIG and MH, while both dynamic and thermodynamic terms play roles in LGM [ABSTRACT FROM AUTHOR]

Overshoot scenarios, in which the forcing reaches a peak before starting to decline, show non-symmetric changes during the CO2 increasing and decreasing phases, producing persistent changes on climate. Non-reversibility mechanisms, associated among others with lagged responses of climate components, changes in ocean circulation and heat transport and changes in the ice cover, bring hysteresis to the climate system. These mechanisms generally have an impact in global scales, potentially generating hemispheric temperature changes and alterations of the Intertropical Convergence Zone (ITCZ). This work analyzes simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to explore the relevance of these mechanisms in overshoot scenarios with different forcing conditions (SSP5-3.4OS and SSP1-1.9) and the impact of these large-scale mechanisms on regional climates, with a particular focus on the degree to which changes in regional extremes are reversible. Results show that non-reversibility of temperature and precipitation extremes mostly occurs during the transition period around the global temperature maximum, when a decoupling between regional extremes and global temperature generates persistent changes at regional level. These changes mainly impact temperature extremes in extratropical regions and precipitation extremes in tropical regions around the ITCZ. In scenarios with strong forcing changes like SSP5-3.4OS, regional non-reversibility can be mostly linked to a temperature asymmetry between Northern and Southern Hemisphere, associated with ITCZ shifts. This asymmetry may be associated with persistent changes in the heat transport and with a different thermal inertia depending on the region, leading regionally to a different timing of the temperature maximum. In scenarios with lower forcing changes like SSP1-1.9, the contribution of this mechanism is more limited and other factors like ice melting may also have a relevant role. [ABSTRACT FROM AUTHOR]

The Pacific Decadal Oscillation (PDO) is the leading mode of sea surface temperature (SST) anomalies in the North Pacific. It dominantly varies on decadal-to-multidecadal timescales, but also fluctuates on interannual timescales. We refer to the latter variability as PDO_IAV in this study. Although it is known that PDO_IAV can be forced by El Niño-Southern Oscillation (ENSO), whether it can feed back to ENSO remains unclear. To address this issue and the resultant possible interaction between PDO_IAV and ENSO, we employ a North Pacific SST pacemaker experiment together with observational data and show that there exists an interaction between PDO_IAV and ENSO, but only for their negative polarity (i.e., –PDO_IAV and La Niña events). Such asymmetry is possibly attributed to winter La Niña-driven Aleutian Low (AL) anomaly, which is displaced more westward relative to that excited by El Niño. As a result, the AL-associated northerly wind anomalies are more prominent over the subtropical northeastern Pacific (SNEP) region, generating marked cold SST anomalies there, which then persist to the following fall. During summer and fall when the climatological Intertropical Convergence Zone is displaced northward, the SST anomalies induce anomalous deep convection, driving a Gill-type response over the tropical Pacific, which produces easterly wind anomalies over the equatorial Pacific. The easterly wind anomalies together with equatorial dynamics further influence central-eastern equatorial Pacific variability, producing a second-year La Niña. Consequently, a –PDO_IAV-La Niña positive feedback is established, which may be an alternative mechanism responsible for the multi-year La Niña phenomenon. [ABSTRACT FROM AUTHOR]

In this study, we discuss the influence of the Southern Indian Ocean Dipole (SIOD) on the location variation of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean and its possible reasons using observations and the Community Earth System Model version 1.0.4 (CESM1.0.4). The results indicate that positive SIOD (PSIOD) and negative SIOD (NSIOD) events in boreal winter have a considerable influence on the ITCZ location over the Indian Ocean in the following year, especially in boreal spring and summer. The observations suggest that the ITCZ shifts northward in the following spring and summer after PSIOD events, while shifts southward after NSIOD events. Numerical simulations with CESM can well reproduce the observed results. We further analyze the correlation between the winter sea surface temperature anomalies over the southern Indian Ocean in SIOD years and the ITCZ location over the Indian Ocean during the following spring and summer, and the results not only confirm that the PSIOD and the NSIOD drive the ITCZ to shift northward and southward, respectively, but also prove that SIOD events show a greater impact on the Indian Ocean ITCZ location in the following spring and summer. In addition, numerical experiments show that the northeast SST of SIOD has a greater impact on ITCZ than the southwest SST. After NSIOD events, the Mascarene high and the Australian high weaken in the following spring and summer, and northwesterly cross-equatorial flow anomalies appear in the equator around 50°E-90°E. Moreover, there is remarkable and anomalous ascending motion over 0°S-20°S, and the ascending branch of the Hadley circulation is southward. Simultaneously, a positive precipitation anomaly appears south of the equatorial Indian Ocean, and the ITCZ over the Indian Ocean moves southward. However, after PSIOD events, the effects on the Indian Ocean ITCZ location in the following spring and summer are roughly opposite to those of NSIOD events. [ABSTRACT FROM AUTHOR]

Increased dust emissions from dryland areas and their effects on human health, ecosystem viability, and environmental change are a global concern in the face of the growing climate crisis. Dust plume emissions from the West African landmass, Sahara, and Sahel areas comprise a major fraction of the global aerosol budget. Dust plume intensity is closely related to regional winds (e.g., Harmattan, Sahara Air Layer), the Intertropical Convergence Zone, monsoonal seasonality, marine currents, and physiography. To study terrigenous material emitted from the continent over the last ~260 kyr (late Quaternary), we used X-ray fluorescence spectroscopy (XRF) to analyze a ~755 cm long marine sediment core from the eastern equatorial Atlantic Ocean, resulting in nearly 1400 discrete measurements. Spectral analysis results suggest that concentrations of elements (Rb, Sr, Si, Al) preserved in the sediments are correlated to different types of orbital climate forcing. Chemical weathering intensity indicated by the Rb/Sr ratio was sensitive to seasonal insolation variations controlled by precession cycles (23–18 kyr), which presumably reflects the relationship between monsoonal rainfall and sensible heating of the continent. Spectral analysis of silicate mineral grain size (Si/Al) showed significant 40 kyr cycles that were paced by obliquity. Based on these data, we infer that winter tradewind activity accelerated in response to the intertropical insolation gradient induced by high obliquity. High Rb/Sr ratios during the last glacial maximum and penultimate glacial maximum may have been due to a predominance of mechanical weathering over chemical weathering under dry/cool climates or the dissolution of Sr-bearing carbonates by corrosive glacial bottom waters. [ABSTRACT FROM AUTHOR]

The Qilian Mountains (QLM) act as an "ecological security barrier" in western China, impacting the downstream ecosystems and water resource utilization. However, the hydrological evolution of the QLM during the last millennium remains controversial, and their ecological response to climate change is poorly understood. We present a pH record based on the brGDGTs (branched glycerol dialkyl glycerol tetraethers) of a 14C-dated sediment core from Lake Maozangtianchi in the QLM. We combined this record with element contents determined by scanning XRF and grain size to reconstruct the summer monsoon precipitation variability over the last 900 years. We also reconstructed the history of eco-environmental changes from the total n -alkane contents. On centennial scales, local precipitation exhibited peaks during the intervals of 1100‒1300 CE and 1750‒2000 CE, as well as between 1400‒1750 CE. Additionally, abrupt decreases in precipitation occurred during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) (1300‒1400 CE). This pattern coherent with other hydroclimatic records from the monsoonal margin of northern China, likely resulted from the combined impact of the El Niño‒Southern Oscillation on tropical Pacific sea-surface temperatures and the meridional shift of the Intertropical Convergence Zone. In addition, a coupled relationship between plant biomass in the Lake Maozangtianchi watershed and fluctuations in monsoon precipitation was observed, with higher plant biomass during 1100‒1200 CE, 1750‒1900 CE, and 1950‒2000 CE, and lower biomass during 1200‒1400 CE and 1900‒1950 CE. However, during 1400‒1750 CE, plant biomass exhibited a minor increasing trend, deviating from its usual correlation with monsoon precipitation. Despite precipitation usually being the primary climatic factor influencing plant biomass in the QLM, during the LIA, nutrients transported by dust and decreased evapotranspiration became pivotal in bolstering plant growth. Our research emphasizes the significant moderating effects of exogenic dust on vegetation changes in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Accurate prediction of sea surface temperatures (SSTs) in the tropical North Atlantic on multiyear timescales is of paramount importance due to its notable impact on tropical cyclone activity. Recent advances in high-resolution climate predictions have demonstrated substantial improvements in the skill of multiyear SST prediction. This study reveals a notable enhancement in high-resolution tropical North Atlantic SST prediction that stems from a more realistic representation of the Atlantic Meridional Mode and the associated wind-evaporation-SST feedback. The key to this improvement lies in the enhanced surface wind response to changes in cross-equatorial SST gradients, resulting from Intertropical Convergence Zone bias reduction when atmospheric model resolution is increased, which, in turn, amplifies the positive feedback between latent and sensible surface heat fluxes and SST anomalies. These advances in high-resolution climate prediction hold promise for extending tropical cyclone forecasts at multiyear timescales. [ABSTRACT FROM AUTHOR]

Taking the Paleozoic of the Sichuan and Tarim basins in China as example, the controlling effects of the Earth system evolution and multi-spherical interactions on the formation and enrichment of marine ultra-deep petroleum in China have been elaborated. By discussing the development of "source-reservoir-seal" controlled by the breakup and assembly of supercontinents and regional tectonic movements, and the mechanisms of petroleum generation and accumulation controlled by temperature-pressure system and fault conduit system, Both the South China and Tarim blocks passed through the intertropical convergence zone (ITCZ) of the low-latitude Hadley Cell twice during their drifts, and formed hydrocarbon source rocks with high quality. It is proposed that deep tectonic activities and surface climate evolution jointly controlled the types and stratigraphic positions of ultra-deep hydrocarbon source rocks, reservoirs, and seals in the Sichuan and Tarim basins, forming multiple petroleum systems in the Ediacaran--Cambrian, Cambrian--Ordovician, Cambrian--Permian and Permian--Triassic strata. The matching degree of source-reservoir-seal, the type of organic matter in source rocks, the deep thermal regime of basin, and the burial-uplift process across tectonic periods collectively control the entire process from the generation to the accumulation of oil and gas. Three types of oil and gas enrichment models are formed, including near-source accumulation in platform marginal zones, distant-source accumulation in high-energy beaches through faults, and three-dimensional accumulation in strike-slip fault zones, which ultimately result in the multi-layered natural gas enrichment in ultra-deep layers of the Sichuan Basin and co-enrichment of oil and gas in the ultra-deep layers of the Tarim Basin. [ABSTRACT FROM AUTHOR]

During the Atlantic References and Convection (ARC) ship campaign with the reference MSM114/2, which took place in early 2023, the German research vessel Maria S. Merian travelled from Mindelo, Cape Verde, to Punta Arenas, Chile. One of the main objectives of ARC was to obtain vertically resolved cross sections of the Intertropical Convergence Zone (ITCZ). To this end, we crossed the ITCZ three times in the meridional direction. We present the atmospheric and oceanographic measurements collected during ARC in a standardized way to facilitate working with data from different instruments and to make the data easily accessible. This approach is not limited to ARC but could serve as a prototype for future (and past) ship campaigns. We present data from the integrated ship sensors (DShip), a Humidity and Temperature Profiler (HATPRO), a Ceilometer, aerosol instruments (DustTrak, Microtops, and Calitoo), radiosondes, Uncrewed Aircaft Vehicles (UAV), and Conductivity, Temperature, and Depth (CTD) profiles of the upper ocean. We distinguish temporal continuous data (DShip, HATPRO, Ceilometer, DustTrak) from point measurements (radiosondes, UAVs, CTDs, Calitoo, Microtops). To illustrate the data sets provided, we present examples of measurements taken during the three crossings of the ITCZ and during a storm in the Roaring Forties in the South Atlantic at the end of the campaign. All data sets can be downloaded from Köhler et al. (2024a). An overview of all available data sets, including dois, can be found here: https://doi.pangaea.de/10.1594/PANGAEA.966616. For references to the individual data sets, please refer to the data availability section. [ABSTRACT FROM AUTHOR]

The Antarctic Oscillation (AAO), which is the main mode of extratropical circulation in the Southern Hemisphere, also has a substantial effect on the Northern Hemisphere climate. We investigated the influence of the early AAO on the frequency of late severe pollution events (SPEF) in the Beijing–Tianjin–Hebei region (SPEFBTH) of China during winter. The results show that the winter (December–January–February) SPEFBTH is negatively correlated with the AAO from the previous autumn (August–September–October). The controlling mechanism can be briefly described as follows: the autumn AAO is positively correlated with the mid‐latitude sea surface temperature (SST) in the South Atlantic Ocean. The SST preserves the autumn anomaly signal into the following winter. This anomalous SST regulates changes in the tropical western Indian Ocean–Intertropical Convergence Zone (IN–ITCZ) via air–sea coupling. Subsequently, as a response to the IN–ITCZ anomalies, anomalous wave trains are excited in the upper troposphere from the tropical western Indian Ocean to East Asia. In addition, the local meridional circulation is modulated; therefore, the circulation field and other meteorological elements favorable for the SPEFBTH appear and exacerbate the SPEFBTH. This study describes a new physical mechanism for the pathway of the AAO influence on subsequent SPEFBTH and finds a predictable source in the Southern Hemisphere air–sea system. Plain Language Summary: The anomalous sea surface temperature in the mid‐latitude Southern Atlantic Ocean and the anomalous Intertropical Convergence Zone in the tropical western Indian Ocean play an important role in the impact of the Antarctic Oscillation on severe pollution events in the Beijing–Tianjin–Hebei region. Key Points: Autumn Antarctic Oscillation and the winter frequency of severe pollution events in the Beijing‐Tianjin‐Hebei region are negatively relatedAutumn Antarctic Oscillation achieves cross‐seasonal and cross‐equatorial impacts via "coupled oceanic‐atmospheric bridge"Sea surface temperature and equatorial convergence zone precipitation anomalies are important components of the air‐sea coupling bridge [ABSTRACT FROM AUTHOR]

The deep ocean, a vast thermal reservoir, absorbs excess heat under greenhouse warming, which ultimately regulates the Earth's surface climate. Even if CO2 emissions are successfully reduced, the stored heat will gradually be released, resulting in a particular pattern of ocean warming. Here, we show that deep ocean warming will lead to El Niño-like ocean warming and resultant increased precipitation in the tropical eastern Pacific with southward shift of the intertropical convergence zone. Consequently, the El Niño-Southern Oscillation shifts eastward, intensifying Eastern Pacific El Niño events. In particular, the deep ocean warming could increase convective extreme El Niño events by 40 to 80% relative to the current climate. Our findings suggest that anthropogenic greenhouse warming will have a prolonged impact on El Niño variability through delayed deep ocean warming, even if CO2 stabilization is achieved. This paper shows that anthropogenic greenhouse warming will have a prolonged impact on El Niño variability through delayed deep ocean warming, even if CO2 stabilization is achieved. [ABSTRACT FROM AUTHOR]

The intertropical convergence zone (ITCZ) is associated with a zonal band of strong precipitation that migrates meridionally over the seasonal cycle. Tropical precipitation also migrates zonally, such as from the South Asian monsoon in Northern Hemisphere summer (JJA) to the precipitation maximum of the west Pacific in Northern Hemisphere winter (DJF). To explore this zonal movement in the Indo-Pacific sector, we analyze the seasonal cycle of tropical precipitation using a 2D energetic framework and study idealized atmosphere–ocean simulations with and without ocean dynamics. In the observed seasonal cycle, an atmospheric energy and precipitation anomaly forms over South Asia in northern spring and summer due to heating over land. It is then advected eastward into the west Pacific in northern autumn and remains there due to interactions with the Pacific cold tongue and equatorial easterlies. We interpret this phenomenon as a "monsoonal mode," a zonally propagating moist energy anomaly of continental and seasonal scale. To understand the behavior of the monsoonal mode, we develop and explore an analytical model in which the monsoonal mode is advected by low-level winds, is sustained by interaction with the ocean, and decays due to the free tropospheric mixing of energy. Significance Statement: Regional concentrations of tropical precipitation, such as the South Asian monsoon, provide water to billions of people. These features have strong seasonal cycles that have typically been framed in terms of meridional shifts of precipitation following the sun's movement. Here, we study zonal shifts of tropical precipitation over the seasonal cycle in observations and idealized simulations. We find that land–ocean contrasts trigger a monsoon with concentrated precipitation over Asia in northern summer and near-surface eastward winds carry this precipitation into the west Pacific during northern autumn in what we call a "monsoonal mode." This concentrated precipitation remains over the west Pacific during northern winter, as further migration is impeded by the cold sea surface temperatures (SSTs) and easterly winds of the east Pacific. [ABSTRACT FROM AUTHOR]

Observed El Niño‐Southern Oscillation (ENSO) varies between decades with high ENSO amplitude and more extreme Eastern Pacific (EP) El Niño events and decades with low ENSO amplitude and mainly weak El Niño events. Based on experiments with the CESM1 model, ENSO may lock‐in into an extreme EP El Niño‐dominated state in a +3.7 K warmer climate, while in a −4.0 K cooler climate ENSO may lock‐in into a weak El Niño‐dominated state. The state shift of ENSO with global warming can be explained by the location and amplitude of the strongest warming over the eastern equatorial Pacific, which amplifies the Bjerknes feedback and allows a southward migration of the Intertropical Convergence Zone onto the equator, a prerequisite of extreme EP El Niños. In light of these results, we discuss to what extent the state of ENSO may be a tipping element in the climate system. Plain Language Summary: El Niño‐Southern Oscillation (ENSO) is the dominant mode of climate variability with far‐reaching impacts. El Niños, the warm events, occur in different flavors. In particular extreme Eastern Pacific (EP) El Niño events are associated with heavy precipitation events and extreme droughts, thus cause large socio‐economic impacts in the Pacific region and beyond. In the observational record, they are quite rare so far. Here we present experiments of one climate model, which suggests that in a warmer climate ENSO may lock‐in in a different state, in which nearly each El Niño is an extreme EP El Niño. On the other hand in a colder climate ENSO may lock‐in in a state with nearly no extreme EP El Niños. In both climates this would have huge consequences for the socio‐economic impacts of ENSO. Against this background we raise the discussion if ENSO may be a tipping element in the climate system. Key Points: El Niño‐Southern Oscillation (ENSO) may be a tipping element in the climate system as its characteristics can be very different under colder or warmer mean climatesIn a warmer climate, ENSO can lock‐in into a state with high variability and nearly each El Niño is an extreme Eastern Pacific (EP) El NiñoMore extreme EP El Niño events would strongly increase the socio‐economic impacts of ENSO [ABSTRACT FROM AUTHOR]

The document titled "Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas Boundary on four continents" discusses the limitations and challenges of radiocarbon and optically stimulated luminescence (OSL) dating methods. It emphasizes the importance of integrating dating methods with other stratigraphic information and using Bayesian analysis to improve accuracy. The document provides information on various sites that have been studied in relation to the Younger Dryas Boundary (YDB) event, including their location, proxies found, and age estimates. It also discusses the evidence of impact-related proxies found at these sites, supporting the hypothesis of a cosmic impact event around 12,800 years ago. The document includes age models, chronological information, and statistical data for specific sites, as well as references to related research. [Extracted from the article]

The Western Tropical Atlantic Ocean (WTAO) is crucial for understanding CO2 dynamics due to inputs from major rivers (Amazon and Orinoco), substantial rainfall from the Intertropical Convergence Zone (ITCZ), and CO2-rich waters from equatorial upwelling. This study, spanning 1998 to 2018, utilized sea surface temperature (SST) and sea surface salinity (SSS) data from the PIRATA buoy at 8°N 38°W to reconstruct the surface marine carbonate system. Empirical models derived total alkalinity (TA) and dissolved inorganic carbon (DIC) from SSS, with subsequent estimation of pH and fCO2 from TA, DIC, SSS, and SST data. Linear trend analysis showed statistically significant temporal trends: DIC and fCO2 increased at a rate of 0.7 μmol kg-1 year-1 and 1.539 μatm year-1, respectively, and pH decreased at a rate of -0.001 pH units year-1, although DIC did not show any trend after data was de-seasoned. Rainfall analysis revealed distinct dry (July to December) and wet (January to June) seasons, aligning with lower and higher freshwater influence on the ocean surface, respectively. TA, DIC, and pH correlated positively with SSS, exhibiting higher values during the dry season and lower values during the wet season. Conversely, fCO2 correlated positively with SST, showcasing higher values during the wet season and lower values during the dry season. This emphasizes the influential roles of SSS and SST variability in CO2 solubility within the region. Finally, we have analysed the difference between TA and DIC (TA-DIC) as an indicator for ocean acidification and found a decreasing trend of -0.93 ± 0.02 mmol kg-1 year-1, reinforcing the reduction in the surface ocean buffering capacity in this area. All trends found for the region agree with data from other stations in the tropical and subtropical Atlantic Ocean. In conclusion, the use of empirical models proposed in this study has proven to help filling the gaps in marine carbonate system data in the Western Tropical Atlantic. [ABSTRACT FROM AUTHOR]

The impact of latitudinal variations in the Intertropical Convergence Zone (ITCZ) on northern Andean hydroclimate during the Medieval Climate Anomaly (MCA; 950–1,150 CE) and Little Ice Age (LIA; 1,300–1,850 CE) is uncertain. Synthesis of two new lacustrine paleoclimate records from the Eastern Colombian Andes with existing circum‐Andean records shows that effective moisture anomalies were synchronous and in phase across the tropical Andes during the last millennium. During the MCA, when the ITCZ was shifted northward, topographically controlled responses in the northern Andes to vigorous atmospheric convection resulted in low precipitation and high evaporation, while precipitation was also reduced in the southern tropical Andes. During the LIA, precipitation decreased in the northern Andes as the ITCZ migrated southward but was offset by cooling that lowered evaporation, establishing high effective moisture. In the southern tropical Andes, the southward ITCZ position simultaneously strengthened precipitation, increasing effective moisture. MCA‐like responses to continued warming trends could similarly reduce northern Andean precipitation while increasing evaporation, thereby lowering effective moisture and possibly reducing water resource availability. Plain Language Summary: The position of the tropical rain belt has been proposed as a leading control on Andean hydroclimate during the Medieval Climate Anomaly (MCA; 950–1,150 CE) and Little Ice Age (LIA; 1,300–1,850 CE), producing opposite hydroclimate conditions in the northern and southern tropical Andes. Using two new paleoclimate records from the eastern Colombian Andes and existing records from the northern and southern tropical Andes, we show that tropical Andean hydroclimate responses were similar, with generally warmer and drier conditions during the MCA and cooler and wetter conditions during the LIA. Whereas southern tropical Andean responses were in line with variations in the tropical rain belt, northern tropical Andean responses were not. For the northern Andes, we propose that slow‐moving, low‐energy convective precipitation during the MCA was blocked by the eastern Andes, resulting in reduced precipitation at elevation and in the interior Andes while warming increased evaporation. Wet conditions in the northern Andes during the LIA were the result of cool atmospheric temperatures that reduced evaporation and increased effective moisture despite low precipitation. This suggests topography and temperature played important roles in the northern Andean hydroclimate and that further warming could reduce effective moisture through topographic precipitation blocking and increased evaporation. Key Points: Tropical Andean hydroclimate variability was synchronous and in‐phase between the northern and southern hemispheres during the last millenniumOrographic influences on atmospheric convection‐controlled precipitation in the northern tropical Andes during the last millenniumMean annual temperatures controlled effective moisture in the northern tropical Andes vis‐à‐vis evaporation [ABSTRACT FROM AUTHOR]

The impact of anthropogenic global warming on tropical cyclone (TC) frequency remains a challenging issue, partly due to a relatively short period of reliable observational TC records and inconsistencies in climate model simulations. Using TC detection from 20 CMIP6 historical simulations, we show that the majority (75%) of these models show a decrease in global-scale TC frequency from 1850 to 2014. We demonstrated that this result is largely explained by weakened mid-tropospheric upward motion in CMIP6 models over the Pacific and Atlantic main development regions. The reduced upward motion is due to a zonal circulation adjustment and shifts in Intertropical Convergence Zone in response to global warming. In the South Indian Ocean, reduced TC frequency is mainly due to the decreased survival rate of TC seeds because of an increased saturation deficit in a warming climate. Our analysis highlights global warming's potential impact on the historical decrease in global TC frequency. [ABSTRACT FROM AUTHOR]

The latitude-altitude structure of the double intertropical convergence zone (DITCZ), its zonal variations, annual cycle and interannual variability over tropical oceans, which were least explored so far, are investigated using the long-term (2006–2018) joint analysis of spaceborne cloud radar and lidar observations that can profile all types of clouds. In contrast to satellite imager observations, this analysis can unambiguously discriminate the DITCZ core and the cirrus outflow emanating from them, which enables the characterization of DITCZ features, including their vertical structure, width and strength even when the equatorial region separating the DITCZ bands has overcast clouds or one of the bands is weak. The role of observed surface wind divergence (SWD) and sea surface temperature (SST) in the genesis and annual migration of the DITCZ bands as well as the ability of vertical wind obtained from reanalysis in capturing the observed DITCZ features are evaluated. The DITCZ occurs over the central Pacific throughout the year, while its occurrence is mainly limited to March-April over the eastern Pacific and the Atlantic and in December over the Indian Ocean. Annual variations of the occurrence, vertical extent, strength and latitudinal positions of the DITCZ bands are mainly driven by the combined effect of SWD and SST variations. The significant differential cloud radiative heating between the equator and the DITCZ bands, derived from the profiles of cloud water content, suggests that it would feedback in enhancing the middle and upper tropospheric wind convergence and downdraft over the equator and contribute to sustain the DITCZ. [ABSTRACT FROM AUTHOR]

This document provides supporting information for an article titled "Bacterial magnetofossil evidence for enhanced Pacific Ocean respired carbon storage during buildup of Antarctic glaciation." It includes details of materials and studied sites, magnetic and geochemical analytical methods, model configuration and boundary conditions for climate simulation experiments, sea-ice fraction simulation results, the age model adopted for the studied sites, parameters associated with components identified from isothermal remanent magnetization (IRM) unmixing analysis, and the BH/BS ratio from TEM results and IRM unmixing. The study collected sediment samples from two sites in the eastern equatorial Pacific Ocean to trace deep Pacific Ocean deoxygenation and its relation to Southern Ocean production variations. Magnetic and geochemical measurements were performed to analyze the sediment samples. This document provides information on sediment ages and climate simulation experiments. Sediment ages were determined using a revised age model, and various fluxes were calculated based on the mass accumulation rate. Climate simulations were conducted using the Community Earth System Model, which consists of multiple components that interact with each other. The simulations were based on the climate state at 35 million years ago and included factors such as vegetation distribution, orbital conditions, and CO2 concentrations. The document also includes figures and tables with additional data and results. The given text appears to be a compilation of data tables and references related to various scientific studies and research papers. The tables include numerical values and ratios related to different samples and measurements. The references provide sources for further reading [Extracted from the article]

The interactions of clouds with radiation influence climate. Many of these impacts appear to be related to the radiative heating and cooling from high‐level clouds, but few studies have explicitly tested this. Here, we use simulations with the ICON‐ESM model to understand how high‐level clouds, through their radiative heating and cooling, influence the large‐scale atmospheric circulation and precipitation in the present‐day climate. We introduce a new method to diagnose the radiative heating of high‐level clouds: instead of defining high‐level clouds as all clouds at temperatures colder than −35°C, we define them as all clouds with a cloud top at temperatures colder than −35°C. The inclusion of the lower cloud parts at temperatures warmer than −35°C circumvents the creation of artificial cloud boundaries and strong artificial radiative heating at the temperature threshold. To isolate the impact of high‐level clouds, we analyze simulations with active cloud‐radiative heating, with the radiative heating from high‐level clouds set to zero, and with the radiative heating from all clouds set to zero. We show that the radiative interactions of high‐level clouds warm the troposphere and strengthen the eddy‐driven jet streams, but have no impact on the Hadley circulation strength and the latitude of the Intertropical Convergence Zone. Consistent with their positive radiative heating and energetic arguments, high‐level clouds reduce precipitation throughout the tropics and lower midlatitudes. Overall, our results confirm that the radiative interactions of high‐level clouds have important impacts on climate and highlight the need for better representing their radiative interactions in models. Plain Language Summary: The interactions of clouds with electromagnetic radiation shape the climate of our planet by causing heating and cooling within the atmosphere. Here, we use a computer model of the atmosphere to investigate how high‐level clouds interact with radiation and thereby influence climate. We find that the interactions of high‐level clouds with radiation strengthen the winds in the midlatitudes and reduce rainfall in many regions. This confirms that high‐level clouds are important for our climate, and highlights the need to improve their representation in our models of the atmosphere and climate. Key Points: We create a method that accurately diagnoses the radiative heating of high‐level clouds by removing artificial cloud boundariesThe radiative interactions of high‐level clouds strengthen the eddy‐driven jet streamThey reduce precipitation in the tropics and lower midlatitudes, but have no substantial effect on the tropical circulation [ABSTRACT FROM AUTHOR]

Understanding the impacts of high‐resolution ocean model provides valuable insights for future research. However, the outcomes of sea surface state changes in both the tropics and mid‐latitudes remain unclear, and initialized seasonal forecasts have not been studied extensively. This study investigates the impact of ocean model resolution with the first long‐term hindcast experiment of an eddy‐resolving (0.1°) ocean model used for global seasonal forecasting. We show that using the high‐resolution ocean model significantly changes boreal winter jet streams in the atmosphere, based on the comparison of 30‐year hindcasts with ocean resolutions ranging from 1° to 0.1° for the Japan Meteorological Agency/Meteorological Research Institute Coupled Prediction System version 3. In boreal winters, the cold sea surface bias in the equatorial Pacific is significantly reduced, leading to an equatorward shift in the intertropical convergence zone (ITCZ) and enhanced convective activity in the western equatorial Pacific. The subtropical jet shifts equatorward due to the ITCZ shift and the weakening of equatorward propagation of mid‐latitude atmospheric eddies. The enhanced convective activity in the tropics has a remote influence in the mid‐latitudes, significantly reducing the upward eddy propagation of zonal wavenumber 1. Sea surface warm‐up in the mid‐latitudes partially cancels the reduction impact by enhancing the zonal wavenumber 2. Overall, the polar night jet accelerates due to the reduced supply of eddy forcing. Plain Language Summary: Atmospheric and oceanic eddies play an important role in shaping the climate. In numerical climate simulations, the Earth is divided into a grid of discrete boxes, and the exchange of energy and mass between the boxes is computed step‐by‐step. Coarse grids are often used to reduce the computational cost, but recent studies have suggested that resolving fine ocean phenomena can make a significant difference. In this study, numerical seasonal forecasting experiments with ocean resolutions of 100 km, 25 km, and 10 km are compared to investigate the high‐resolution effects on the atmospheric flow for boreal winter. This is the first 30‐year‐long, retrospective seasonal forecast experiment for the past winters using a global eddy‐resolving (10 km) ocean model. The high‐resolution ocean model greatly warms the surface seawater in the tropical Pacific and in the mid‐latitude oceans. These changes in the sea surface influence atmospheric convection and eddies, with far‐reaching effects on distant regions and altitudes. Such effects on the westerly jet streams, which flow several kilometers to tens of kilometers above the sea surface, are observed in the southward shift of the subtropical jet and the strengthening of the polar night jet. Key Points: Altering the ocean model resolution from 1° to 0.1° in a seasonal forecast model shifts and enhances the subtropical and polar night jetsAtmospheric responses to both tropical and mid‐latitude oceans are observedWave‐mean flow diagnostics indicates that the jet stream responses are more strongly influenced by the tropics [ABSTRACT FROM AUTHOR]

The mid-Brunhes dissolution interval (MBDI; Marine Isotope Stage (MIS) 13 to 7; ~ 533–191 ka) is characterized by various paleoclimatic/paleoceanographic events in the world. We investigated fossil deep-sea benthic foraminifera and sediment geochemistry at the onset of the MBDI (~ 670–440 ka) using Ocean Drilling Program (ODP) Site 758 and core GPC03 in the northeast tropical Indian Ocean (TIO), primarily focusing on the relationship between the paleoceanographic conditions of the surface and deep oceans. Based on multi-dimensional scaling, MDS axis 1 is related to the specific depth habitats of benthic foraminiferal fauna, possibly at the trophic level. In MDS axis 1, the difference between the two core sites was smaller from ~ 610 to 560 ka, whereas it was larger from ~ 560 to 480 ka. In contrast, MDS axis 2 may be related to the low food supply at episodic food pulses/relatively stable and low food fluxes. MDS axis 2 showed generally similar stratigraphic variations between the two cores during ~ 610–560 ka, but was different during ~ 560–480 ka. The proportion of lithogenic matter to biogenic carbonate was relatively low from ~ 610 to 530 ka under the highstand when sediment transport to the study area was reduced. Thus, both the depth gradient in the distribution of benthic foraminiferal fauna and the lithogenic supply between the two cores changed coincidently across the MIS 15/14 (~ 570–540 ka) transition. Such paleoceanographic conditions across MIS 15/14 transition were attributed to the long-term weakening of the wind-driven mixing of surface waters, which might have been caused by the weakening of the Indian summer monsoon in the northeast TIO, possibly with the northward displacement of the InterTropical Convergence Zone in the Northern Hemisphere. In particular, the depth gradient in the distributions of benthic foraminiferal faunas represents the paleoceanographic linkage between the surface and deep oceans through particulate organic matter ballasting by calcareous plankton skeletons in addition to lithogenic matter, which changed transiently and significantly across MIS 15/14 transition close to the onset of the MBDI. [ABSTRACT FROM AUTHOR]

A recent study published in the Journal of Biogeography provides evidence of a century-long drought on Rapa Nui, also known as Easter Island, between 1570 CE and 1720 CE. The drought was identified through sedimentary gaps and the desiccation of Lake Raraku, one of the island's freshwater sources. The study suggests that the drought coincided with major ecological and cultural transformations, including deforestation and a shift from the moai cult to the Birdman cult. The potential causes of the drought, such as shifts in the subtropical storm track or the El Niño Southern Oscillation, are still being debated. The study also highlights the importance of the Environment-Human-Landscape Feedbacks and Synergies framework for understanding the complex interactions between climate, vegetation, and human activities on the island. Further research is needed to explore the causes of the drought and its ecological and cultural impacts. [Extracted from the article]

The Doldrums transform system, located in the Equatorial Atlantic at 7–8°N, is a 110 km-wide multi-fault shear zone, with five active transform faults separated by four short intra-transform ridge segments (ITRs). The two central ITRs, ITR-2 and ITR-3, are significantly deeper than the peripheral ridge segments, suggesting differences in the thermal conditions of the sub-ridge mantle. New chemical and radiogenic isotope data from on-axis lavas erupted across the transform domain reveal that the basalts from ITR-3 are enriched in alkalis (Na 2 O + K 2 O = 4.3 wt%; Na 8 up to 3.7) and light rare earth elements (La/Sm) N = 0.86–0.97). However, these basalts have lower Sr and Pb isotope ratios than MORB from the Equatorial Atlantic (i.e., 87Sr/86Sr ∼ 0.70237 and 206Pb/204Pb ∼ 18), and relatively high Nd and Hf isotope ratios (143Nd/144Nd = 0.51315–0.51325; 176Hf/177Hf = 0.2832–0.28325). Hence, the mantle underlying ITR-3 is, on average, depleted in highly incompatible elements. Thermal models of the sub-ridge mantle show that it is also the coldest mantle region under the Doldrums system with the lowest crust production. Considering its location in the central transform domain, it is likely that the local mantle underwent melting beneath adjacent segments of the Mid-Atlantic Ridge (MAR) before remelting below ITR-3. We propose that the initial melting event beneath the MAR selectively removed the most fusible, geochemically enriched mantle components, leaving behind a predominantly peridotitic source, characterized by comparatively low Sr and Pb isotope ratios. Therefore, MORB from intra-transform ridge segments, such as those within the Doldrums transform system, provide a rare opportunity to constrain the isotopic composition of highly incompatible element depleted peridotitic mantle, which is a ubiquitous, but otherwise often camouflaged component of Earth's mantle. [ABSTRACT FROM AUTHOR]

The profound impact of the Khmer Empire on Southeast Asia renders the Angkor Period particularly significant in guiding contemporary societies to advocate and promote policies that respond to climate change. We present a new continuous multi-proxy speleothem dataset from Tonle Sap Lake Basin, investigating hydroclimate variability and the paleoenvironment of Cambodia during the Angkor Period from the 9th to 15th centuries. In addition, two important climatic events on a decadal scale are clearly reconstructed. The first is the reduction of precipitation between 800 and 1000 AD and the relatively significant drought that the regional environment may have experienced from 950 to 1000 AD. The second is the anomalous wet period between 1000 and 1200 AD, during which the Southern Oscillation Index also reached its negative peak after a thousand years. The wet and dry conditions are highly consistent with the El Niño-dominated and northward Intertropical Convergence Zone. [ABSTRACT FROM AUTHOR]

As the community increases climate model horizontal resolutions and experiments with removing moist convective parameterizations entirely, it is imperative to understand how these advances affect the InterTropical Convergence Zone (ITCZ). We investigate how the ITCZ responds to deactivating parameterized convection at two resolutions, 50 and 6 km, in fixed sea surface temperature, aquaplanet simulations with the NOAA GFDL AM4 atmospheric model. Disabling parameterized convection at 50 km resolution narrows the ITCZ and increases its precipitation minus evaporation (P–E) maximum by ∼78%, whereas at 6 km resolution doing so widens the ITCZ and decreases its P–E maximum by ∼50%. Using the column‐integrated moist static energy budget, we decompose these tropical P–E responses into contributions from changes in atmospheric energy input (AEI), gross moist stability, and gross moisture stratification. At 6 km, the ITCZ weakens due to increased gross moist stability. Disabling the convective parameterization at this finer resolution deepens the circulation, favoring more efficient poleward energy transport out of the deep tropics and reduced precipitation in the core of the ITCZ. Conversely, at 50 km the ITCZ strengthening is primarily driven by AEI, which in turn stems primarily from increased low cloud amount and thus longwave cloud radiative cooling in the Hadley cell subsiding branch. The Hadley circulation overturning intensifies to produce poleward energy fluxes that compensate the longwave cooling, yielding a stronger ITCZ. We further show that the low level diabatic heating profiles over the descending region are instrumental in understanding such diverse responses. Plain Language Summary: About one‐third of Earth's precipitation falls within a narrow band near the equator, the InterTropical Convergence Zone (ITCZ). In this study, we investigate two modeling choices that affect the ITCZ: (a) the horizontal resolution of the model and (b) the convective parameterization, which controls how heat and water ascend within thunderstorms and clouds. We conduct four simulations using an idealized climate model setup that assumes the globe is wholly ocean with unchanging surface temperatures. One pair of simulations is conducted at 50 km resolution and the other pair of simulations is conducted at 6 km resolution. Both pairs of simulations compare the ITCZ with and without an active convective parameterization. The ITCZ precipitation maximum nearly doubles when deactivating the convective parameterization at 50 km resolution, however, at 6 km resolution, the ITCZ precipitation maximum halves. The reasons for these disparate ITCZ changes relate to how much, and how efficiently, energy is transported by the Hadley circulation. Whereas at 50 km, deactivating the convective parameterization promotes low clouds that cool the subtropics, accelerating the Hadley circulation and raising precipitation, at 6 km, deactivating the convective parameterization instead increases the efficiency with which energy is transported by the Hadley circulation, reducing precipitation. Key Points: Disabling parameterized convection changes the InterTropical Convergence Zone (ITCZ) precipitation minus evaporation maximum by +78% and −50% at 50 and 6 km resolutionsDisabling parameterized convection at 6 km resolution deepens the Hadley circulation, increasing gross moist stabilityDisabling parameterized convection at 50 km resolution increases subtropical cloud radiative cooling, intensifying the Hadley circulation [ABSTRACT FROM AUTHOR]

The response of low-latitude weather and climate to polar sea ice melt is not well understood. In this study, we run a suite of fully coupled simulations using the Community Earth System Model to investigate the effects of polar sea ice melt on Indian summer monsoon (ISM). In the coupled model simulation, the albedo of the sea ice is reduced in such a way that the increased absorption of the solar radiation would melt the sea ice. The effects of the Arctic and Antarctic sea ice melts on the ISM have been examined. The findings reveal that the combined melting of sea ice in the Arctic and Antarctic exerts a stronger influence on the ISM compared to the melting at a single pole. Specifically, the ISM exhibits a relatively weak sensitivity to the Arctic sea ice melt, while showing a stronger response to sea ice melt over the Antarctic and the combined melt over both poles. The response of summer monsoon to sea ice melt is characterized by a weakening of the circulation and a decrease in the continental precipitation, indicating an overall weakening of the monsoon system as a result of the polar sea ice melt. The intertropical convergence zone (ITCZ) and associated precipitation pattern shift equatorward in the sea ice melt experiments. [ABSTRACT FROM AUTHOR]

Understanding the variability and related dynamic mechanisms of the Indian summer monsoon evolution over the past millenniums is crucial for disaster prevention and mitigation in the context of strengthening global warming. Here, we present a high‐resolution hydroclimate reconstruction over the past 3110 years in northwestern Yunnan Province, southwestern China, based on grain size analysis using the End‐member modeling algorithm and other environmental proxies. The results indicate that the temperature in northwestern Yunnan Province generally decreased since 3110 cal. yr BP, aligning with other temperature records on regional and global scales. Precipitation in the study area remained relatively stable before 1000 cal. yr BP, but exhibited an obvious out‐phase change compared with the temperature records over multidecadal to centennial timescale. While after 1000 cal. yr BP, the precipitation steadily increased, revealing the hydroclimate pattern of notably dry Medieval Warm Period (MWP) and relatively wet Little Ice Age (LIA) in the study area. The decoupling combination of temperature and precipitation spanning the MWP and LIA in southwestern China contrasts with that in the East Asian summer monsoon area and the Indian subcontinent which is also controlled by the Indian summer monsoon, indicating the spatial heterogeneity of precipitation in the Asian summer monsoon region. The discussion about dynamic mechanisms points out that solar activity emerges as a significant factor influencing regional temperature changes, and El Niño‐Southern Oscillation and Intertropical Convergence Zone migration jointly impact the precipitation change in the study area and the hydroclimate discrepancy in the Asian summer monsoon region. Plain Language Summary: Knowledge of the Indian summer monsoon evolution over the past millennium is vital for addressing the challenges posed by global warming. In this study, we present a high‐resolution hydroclimate reconstruction covering the last 3110 years in northwestern Yunnan Province, southwestern China. Using the End‐member Modeling Algorithm and multiple environmental proxies, we found a general temperature decrease since 3110 cal. yr BP, consistent with global and regional trends. Before 1000 cal. yr BP, precipitation in the study area remained stable but showed a distinct antiphase pattern with temperature variations over multidecadal to centennial timescales. After 1000 cal. yr BP, precipitation steadily increased, revealing a notably dry Medieval Warm Period (MWP) and a relatively wet Little Ice Age (LIA). The decoupling of temperature and precipitation during the MWP and LIA in southwestern China contrasts with the East Asian summer monsoon and the Indian subcontinent, highlighting the spatial heterogeneity of precipitation in the Asian summer monsoon (ASM) region. Our discussion on dynamic mechanisms highlights the significant role of solar activity in regional temperature changes and the joint impact of El Niño‐Southern Oscillation and Intertropical Convergence Zone migration on precipitation in the study area and the broader ASM region. Key Points: Precipitation change in the study area was indicated by the relative proportion of end membersDecoupling warming and monsoon precipitation in northwestern Yunnan Province was revealedEl Niño‐Southern Oscillation and Intertropical Convergence Zone migration jointly impact the hydroclimate discrepancy in the Asian summer monsoon region [ABSTRACT FROM AUTHOR]