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The study employed high-resolution atmospheric general circulation models (AGCM) to simulate tropical cyclones (TCs) and evaluated two TC genesis potential indices in reflecting projected TC changes in the western North Pacific (WNP) under a warming scenario. Both indices accurately represented the seasonal variation of TC genesis frequency (TCGF) and its spatial distribution in historical simulations and observation data. The widely-used TC genesis potential index (χGPI) projected a significant increase in TCGF in response to a warmer ocean surface. However, this projection conflicted with the significant reduction in the model projection due to the dominant control of SST on the χGPI. Higher SST in remote ocean basins often over dominated the destabilization effect of in-situ warmer SST and caused more stable atmospheric conditions in the WNP, resulting in fewer TC occurrences. By contrast, the revised index (χMqGPI), which considers gross moisture condensation, projected a TCGF decrease that more accurately reflected the decreasing trend of TCGF in the warming simulations by AGCM, although the degree of reduction was smaller than that derived directly from TC detection scheme. The results suggest the plausibility of using χMqGPI, based on the results of multimodel coarse-resolution CMIP6 climate models, to project future changes in TCGF in the WNP.

Abstract Convective afternoon rainfall (CAR) is a significant summer rainfall feature in Taiwan. This study investigates the projected uncertainties in summer CAR in Taiwan, using a dynamical downscaling approach with the Weather Research and Forecasting Model (WRF) and the High-Resolution Atmospheric Model (HiRAM). The projections were driven by four different sea surface temperature (SST) categories derived from CMIP5 model simulations under the RCP8.5 scenario. All projections indicate a reduced frequency but increased intensity of CAR over Taiwan by the end of the 21st century. However, notable differences in the degree of CAR changes were observed among simulations with varying degrees of Pacific SST warming. These variations in potential future changes in CAR frequency and intensity can be attributed to the variations in daytime thermal instability, local inland wind convergence, and moisture flux convergence over Taiwan. Furthermore, this study explored the linkage between local thermodynamic conditions and projected large-scale circulation patterns.

Abstract In boreal summer of 2022, Pakistan experienced extremely high rainfall, resulting in severe flooding and displacing over 30 million people. At the same time, heatwaves persisted over central China and Europe. The coexistence of these extreme events suggests a possible linkage. Our analysis indicated that the record rainfall was mainly induced by compounding factors. These included (1) La Niña-induced strong anomalous easterlies over the northern Indian subcontinent, (2) intense southerlies from the Arabian Sea with an upward trend in recent decades, (3) an interaction between extratropical and tropical systems, specifically the northerly flow downstream of the Europe blocking and the southerly monsoon flow from the Arabian Sea. Wave activity flux and regression analyses unveiled a distinct stationary Rossby wave-like pattern connecting the flooding in Pakistan and heatwaves in Europe and China. This pattern, an emerging teleconnection pattern in recent decade, exhibited substantial differences from the reported teleconnection patterns. We also noted the positive feedback of the excessive Pakistan rainfall could further enhance the large-scale background flow and the heavy rainfall itself. The 2022 Pakistan flood event was an intensified manifestation of the 2010 Pakistan flood event, which was also caused by compounding factors, but occurred in a more pronounced upward trend in the both tropics and extratropics.

Abstract Due to the cold water temperatures, the East China Sea (ECS) is usually unfavorable for typhoon development. Recently, in a rare event, Typhoon Bavi (2020) reached major typhoon status and became the strongest typhoon in the ECS in the past decade. Based on in situ observations and model simulations, we discover that this typhoon is fueled by a marine heatwave, which creates a very warm ocean condition with sea surface temperature (SST) exceeding 30 °C. Also, because of suppressed typhoon-induced SST cooling caused by the shallow water depth (41 m) and strong salinity stratification (river runoff) within the ECS, the SST beneath the typhoon remains relatively high and enhances the total heat flux for the typhoon. More interestingly, due to the fair weather ahead of the typhoon, we find that the rapid development of this marine heatwave is likely, in part, attributed to the typhoon itself. As the risks from typhoons and marine heatwaves are heightening under climate change, this study provides important insights into the interaction between typhoons and marine heatwaves.

A record-breaking heatwave event occurred in western North America in the summer of 2021. Previous studies on a similar event's uniqueness and return period are typically estimated based on extreme value analysis and statistics of selected stations or area-mean temperature data. The extreme statistics results are no longer valid if moved to another location. Further, the detailed evolution of spatial extent and intensity through its duration is not quantified and compared to other historical heatwave events to claim its rarity and severity. By applying an event detection and tracking algorithm to heatwaves, we first construct an archive for all the events over the region since 1979 based on daily maximum temperature data from reanalysis. It documented the daily mean temperature anomalies, affected areas, and durations of all individual heatwave events. It is, therefore, possible to objectively compare and rank the magnitudes of all historical heatwave events by examining the total integrated effects from the intensity, impact region, and duration. With the global mean warming background increase of about 0.4 °C from 1979 to 2000 to 2000–2021, we found that the mean integrated magnitude and size of the top 100 heatwave events increased significantly by 155 ± 88%. The dominant relative contributions to this integrated severity measure increase are +78 ± 39% from the mean affected area, followed by +54 ± 21% from duration and +7 ± 4% from the intensity. With the above analyzed general historical increasing trend of heatwave event metrics, the severity of the 2021 summer heatwave over the region was due to a combination of its record-breaking event-mean spatial coverages (2090383 km2), highest normalized daily maximum temperature anomalies and long duration (11 days, in the top 4% of all heatwave events). This integrated severity measure of the event was more than double of any other historical heatwave event and about 17 times larger than the mean severity of all heatwave events over the region.

Combined with other westerly-sensitive records, a new stalagmite hydroclimate record from northern Italy reveals changing westerly wind directions over the past 6500 years that correspond to a migration of the North Atlantic centres of action.

Abstract A robust understanding of the sub-seasonal cold season (November–March) precipitation variability over the High Mountains of Asia (HMA) is lacking. Here, we identify dynamic and thermodynamic pathways through which natural modes of climate variability establish their teleconnections over the HMA. First, we identify evaporative sources that contribute to the cold season precipitation over the HMA and surrounding areas. The predominant moisture contribution comes from the mid-latitude regions, including the Mediterranean/Caspian Seas and Mediterranean land. Second, we establish that several tropical and extratropical forcings display a sub-seasonally fluctuating influence on precipitation distribution over the region during the cold season. Many of them varyingly interact, so their impacts cannot be explained independently or at seasonal timescales. Lastly, a single set of evaporative sources is not identifiable as the key determinant in propagating a remote teleconnection because the sources of moisture anomalies depend on the pattern of sub-seasonally varying dynamical forcing in the atmosphere.

In this paper, we demonstrate that the extreme cold snap in Texas in February 2021 resulted from a large-scale background circulation anomaly over the North Pacific and North America that was a manifestation of both natural variability (namely, a negative Pacific–North American pattern, PNA) and a warming trend that began in the late 1990s. Numerical experiments revealed that the negative PNA pattern could be driven by negative (La Niña-like) sea surface temperature (SST) anomalies in the equatorial eastern Pacific on an interannual–decadal timescale and the SST warming trend in the subtropical North Atlantic on a longer timescale. We propose that the excitation of the most unstable mode of the Northern Hemisphere winter, which exhibits a combined negative PNA and positive East Atlantic pattern resulting from SST anomalies and trends, leads to the dominance of the large-scale circulation anomaly observed in February 2021 and over the last few decades.Our study demonstrated the key role of extratropical wave activity and the intrinsic mode in causing the extreme cold in North America. The arguments favoring polar or tropical influences may partially explain the source of variability, considering that extratropical weather and climate variability could be modulated by not only polar or tropical perturbations but also the enhanced tropical–extratropical interaction and mid-latitude instability. A systematic approach involving both empirical diagnostics and a suite of carefully designed numerical experiments is required to determine the relative influence of various sources of variability.Regarding future changes, models of the Coupled Model Intercomparison Project Phase 6 project a weakening, rather than an enhancement, of the negative PNA pattern that favors the occurrence of cold snaps despite failing to simulate the observed enhanced trend since the late 1990s.

The falling ice (snow) radiative effects (FIREs) have previously been shown to contribute substantially to reduced discrepancies in simulations of present-day climatology of radiation, skin temperatures and sea ice concentration and thickness over the Southern Ocean. This study extends to examine the impacts of FIREs on simulation of sea ice changes under a scenario of gradual increase of atmospheric CO2 concentration. We perform a pair of sensitivity experiments including (CESM1-SoN) and excluding (CESM1-NoS) FIREs using Community Earth System Model version 1. The differences in the annual and seasonal means between the initial and warmer periods are examined. Relative to CESM1-SoN, CESM1-NoS simulates more surface reflected shortwave and less downward longwave radiative warming, as well as colder surface temperature, resulting in larger annual-mean sea ice extent and thickness and slower seasonal and long-term sea ice melting and thinning. Over the Southern Ocean of CESM1-SoN, reduced downwelling longwave radiation in austral winter (June-July-August: JJA) leads to sea-ice growth with colder skin temperature while reduced net radiation resulting from increased shortwave reflection in austral summer reduces the melting of sea ice with little change in skin temperature. CESM1-NoS shows seasonal and long-term trends similar to those in CMIP5 models that exclude FIREs, hinting slower future warming-driven changes and larger amplitude of the annual cycle in sea ice concentration and thickness. The ice-free Southern Ocean in peak melting season is simulated at approximately year 130 for CESM1-NoS but year 100 for CESM1-SoN, about 30 years later than that of the Arctic.

Most global climate models, such as CMIP5 models, ignore the falling ice (snow) radiative effects (FIREs). Extended from our previous works, we explore the impacts of FIREs on the geographical distribution changes of sea ice concentration (SIC), sea ice thickness and skin temperature (Ts) under 1% per year increase of atmospheric CO2 concentration. We perform a pair of 140-year experiments including FIREs (SoN) and excluding FIREs (NoS) using CESM1-CAM5. These two simulations are compared with each other and against CMIP5 multi-model mean without FIREs (CMIP5-NoS). The results show that the changes of SIC, thickness and radiation fields in NoS minus SoN largely match the changes between CMIP5-NoS and SoN in winter but less so in summer and annual mean. Both NoS and CMIP5-NoS simulate less downward longwave and net radiative warming (~20 - 30 W m-2), resulting in colder Ts over Arctic and adjacent lands (~5 - 8 K colder) and stronger meridional temperature gradient, leading to more SIC and thicker sea ice (~30 - 40 cm) over the Arctic ocean. The inclusion of FIREs produces stronger changes in geographic patterns and magnitudes of Ts, SIC and thickness from the first to middle 20 years but less from the middle to last 20 years. The SIC and thickness changes in SoN are associated with warmer Ts, increasing downward surface longwave warming and thus net warming relative to NoS and CMIP5-NoS. With FIREs, the model shows faster warming-driven sea ice retreats and thinning over the entire Arctic ocean, resulting in a sea ice-free Arctic ocean 30 years earlier, as well as much warmer Ts (up to 5 K) over the adjacent lands than in NoS case.

Precipitation in the spring and Mei-yu seasons, the main planting and growing period in East Asia, is crucial to water resource management. Changes in spring and Mei-yu extreme precipitation under global warming are evaluated based on two sets of high-resolution simulations with various warming pattern of sea surface temperature (SST'spa). In the spring season, extreme precipitation exhibits larger enhancements over the northern flank of the present-day prevailing rainy region and a tendency of increased occurrence and enhanced intensity in the probability distribution. These changes imply a northward extension of future spring rainband. Although the mean precipitation shows minor change, enhanced precipitation intensity, less total rainfall occurrence, and prolonged consecutive dry days suggest a more challenging water resource management in the warmer climate. The projected enhancement in precipitation intensity is robust compared with the internal variability related to initial conditions (σˆint) and the uncertainty caused by SST'spa (σˆΔSST). In the Mei-yu season, extreme precipitation strengthens and becomes more frequent over the present-day prevailing rainband region. The thermodynamic component of moisture flux predominantly contributes to the changes in the spring season. In the Mei-yu season, both the thermodynamic and dynamic components of moisture flux enhance the moisture transport and intensify the extreme precipitation from southern China to northeast Asia. Compared with spring season, projecting future Mei-yu precipitation is more challenging because of its higher uncertainty associated with 1) the σˆint and σˆΔSST embedded in the projections and 2) the model characteristics of present-day climatology that determines the spatial distribution of precipitation enhancement.

Interdecadal variability of northward-propagating ISOs from July to September is examined by dividing the 32 years into 1979 - 1993 and 1994 - 2010. The enhanced easterly anomalies in 1994 - 2010 could increase the steering flow for the submonthly wave pattern and TCs. Therefore, the propagation routes for TCs and submonthly wave patterns were pushed farther westward toward eastern China in 1994 - 2010 instead of slowly migrating northward to Japan in 1979 - 1993. By separating the background flow into the climatological mean and ISO components, a sensitivity study of the barotropic interaction is conducted when switching the background flow of the other epoch. The results show that the enhancement of the subtropical anticyclone in the later epoch changes the distribution of the background easterly flow and thus the barotropic conversion maximum between the submonthly perturbations and climatological circulation was displaced westward. The strengthening of the ISO background fields in the later epoch enhances the barotropic interaction between the ISO and submonthly perturbations. Thus in the westerly phase of the later epoch, the enhanced ISO cyclonic anomaly favors the barotropic conversion to intensify. The positive areas of interdecadal changes for the barotropic conversion between the submonthly perturbations and the climatological mean fields are co-located with the positive changes due to the ISO background fields where the wave pattern and TCs move further westward in the later epoch. Therefore, the interdecadal impacts by the climatological mean fields and ISO on the energy conversion jointly favor the development of the wave pattern and TCs.

Non-technical summary We summarize what we assess as the past year's most important findings within climate change research: limits to adaptation, vulnerability hotspots, new threats coming from the climate–health nexus, climate (im)mobility and security, sustainable practices for land use and finance, losses and damages, inclusive societal climate decisions and ways to overcome structural barriers to accelerate mitigation and limit global warming to below 2°C. Technical summary We synthesize 10 topics within climate research where there have been significant advances or emerging scientific consensus since January 2021. The selection of these insights was based on input from an international open call with broad disciplinary scope. Findings concern: (1) new aspects of soft and hard limits to adaptation; (2) the emergence of regional vulnerability hotspots from climate impacts and human vulnerability; (3) new threats on the climate–health horizon – some involving plants and animals; (4) climate (im)mobility and the need for anticipatory action; (5) security and climate; (6) sustainable land management as a prerequisite to land-based solutions; (7) sustainable finance practices in the private sector and the need for political guidance; (8) the urgent planetary imperative for addressing losses and damages; (9) inclusive societal choices for climate-resilient development and (10) how to overcome barriers to accelerate mitigation and limit global warming to below 2°C. Social media summary Science has evidence on barriers to mitigation and how to overcome them to avoid limits to adaptation across multiple fields.

This study aims to characterize the interhemispheric teleconnection pattern, which is established by the South America (SA) summer monsoon over the Atlantic Ocean during January and February, and referred it as the Atlantic symmetric pattern (ASP). The ASP is characterized using the leading mode of interannual sea surface temperature (SST) variability of the Southwest Atlantic Ocean, where strong convection-SST coupling occurs. The pattern is manifested as two anomalous cyclonic-anticyclonic-cyclonic circulation trains aligned meridionally over the Atlantic Ocean, with a distinct SST dipole of the Southwest Atlantic Ocean and a tripole of the North Atlantic Ocean. The interhemispheric wave trains of the ASP are excited as a Gill-type response to convective activity in the SA summer monsoon, as confirmed in linear baroclinic model. Complementing previous studies on observed interhemispheric connection in the Atlantic, our findings highlight the importance of characterizing the ASP and its role in linking the South Atlantic SST, the SA summer monsoon, and North Atlantic climate. Further research is warranted to explore the impacts of the ASP on the Northern Hemisphere and its interactions with other climatic modes.

The Northeast Pacific (NEP) had two record-breaking marine heatwave events in the winters of 2013–2015 and summer of 2019, which had a detrimental impact on the fisheries, marine ecosystems, and climate in North America. Here, we investigated the cause of sea surface temperature (SST) variability in NEP during late spring–summer of 1981–2020. The regression circulation anomalies to the principal component of leading empirical orthogonal function mode suggested that the warm NEP SST were characterized by a cyclonic circulation anomaly in the midlatitude North Pacific and a warming SST center in the Gulf of Alaska. We noted that this cyclonic circulation anomaly, attributable to a barotropic atmospheric wave originating from the tropical central Pacific (CP) in the preceding spring, reduced the surface heat flux loss from the ocean to the atmosphere in the NEP and led to the warm SST anomalies in summer. This finding was confirmed by not only empirical diagnosis but also long-term numerical simulations forced by the observed SST perturbations in the tropical CP. Our results highlight the role of the tropical CP SST in driving the summertime North Pacific SST variability through the atmospheric bridge in recent decades.

Abstract This study evaluates the performance of the Taiwan Earth System Model version 1 (TaiESM1) in simulating the observed climate variability in the historical simulation of the Coupled Model Intercomparison Phase 6 (CMIP6). TaiESM1 is developed on the basis of the Community Earth System Model version 1.2.2, with the inclusion of several new physical schemes and improvements in the atmosphere model. The new additions include an improved triggering function in the cumulus convection scheme, a revised distribution‐based formula in the cloud fraction scheme, a new aerosol scheme, and a unique scheme for three‐dimensional surface absorption of shortwave radiation that accounts for the influence of complex terrains. In contrast to the majority of model evaluation processes, which focus mainly on the climatological mean, this evaluation focuses on climate variability parameters, including the diurnal rainfall cycle, precipitation extremes, synoptic eddy activity, intraseasonal fluctuation, monsoon evolution, and interannual and multidecadal atmospheric and oceanic teleconnection patterns. A series of intercomparisons between the simulations of TaiESM1 and CMIP6 models and observations indicate that TaiESM1, a participating model in CMIP6, can realistically simulate the observed climate variability at various time scales and are among the leading CMIP6 models in terms of many key climate features.

Equatorial Rossby waves (ERWs) are manifest as westward-propagating, planetary- scale waves that feature a symmetric pair of pressure and zonal wind fields about the equator. ERWs can modulate tropical convective activity, especially in South Asia and the Maritime Continents, and represent an important mode of intraseasonal variability additional to the Madden-Julian Oscillation. Changes in the frequency and intensity of ERWs during the recent decades were investigated based on observations of tropospheric winds and tropical convection. Spectral analyses indicated that ERWs appear to have intensified especially in the upper troposphere; this is associated with increased convective activity located off the equator. The strengthening and westward shift of the Walker circulation observed in the recent decades acted to increase the tropical vertical westerly shear and, subsequently, may contribute to the increased ERW activity. Further investigation on the dynamical process of the vertical zonal shear enhancement will improve the understanding of the changing ERW characteristics.

This study evaluates the performance of the Coupled Model Intercomparison Project Phases 6 models (CMIP6) in simulating the seasonal evolution and extreme precipitation indices in the western North Pacific and East Asia region (WNP-EA), and compare the results with those from CMIP Phases 5 (CMIP5). In the ensemble of CMIP6 models, the seasonal evolution simulation demonstrates improvements in seasonal northward migration of the rain band from spring to summer and more intense precipitation, resulting in a higher skill score in the CMIP6 ensemble than the CMIP5 one. In general, the skill scores for the spatial pattern of simple daily intensity (SDII), total rainfall occurrence (Totfq), and consecutive dry days (CDD) are higher than those of extreme precipitation intensity (R99p). The CMIP6 ensemble mostly gains higher skill scores for extreme precipitation indices in the wet season. However, the improvement is limited in extreme indices during spring and fall. The probability distributions for maximum 1-day precipitation (RX1day), maximum 5-day precipitation (RX5day), and R99p in the CMIP6 models demonstrate a more realistic shape and stronger intensity, indicating the improvement over the CMIP5 models. However, the biased distributions of the overestimated (underestimated) occurrence for lighter (heavier) SDII and shorter (longer) duration CDD cases remain as a problem in CMIP6 model simulations. The higher skill scores for the spatial pattern of SDII, Totfq, and CDD are likely due to the compensation between the biased distributions mentioned above, implying further improvements are needed for correcting the deficiency in simulating the precipitation occurrence.

Abstract Future changes in the frequency and destructiveness of landfalling tropical cyclones (TCs) over East Asia were investigated by analyzing the simulations of two high‐resolution (20–25‐km) atmospheric general circulation models forced by sea surface temperature (SST) in the present period (1979–2003) and under future warming conditions (2075–2099) of the RCP8.5 scenario. The present‐day simulations capture well the genesis count, tracks, and intensity associated with TCs striking the coastal areas of Taiwan‐East China (TWCN), the South China Sea‐Indochina (SCS) and the vicinity of Japan (JP). The frequency of landfalling TCs over TWCN, SCS, and JP is projected to nearly half by the end of the 21st century. However, these landfalling TCs induce enhanced destructive threats of stronger winds and heavier precipitation under the future warmer climate. Through attribution analysis we found the reduced frequency of landfalling TCs to be mainly caused by a decline in TC genesis count (rather than TC track changes), while the increased intensity of landfalling TCs is linked with changes in the TC intensification rate (as opposed to duration changes). Diagnoses of the genesis potential index and eddy energetics further suggest that the mid‐tropospheric drying and weakened synoptic‐scale eddy activity resulting from anticyclonic and downward circulations over the main TC genesis region create an unfavorable environment for TC genesis. In contrast, warmer SST, reduced vertical wind shear and enhanced efficiency of eddy kinetic energy generations appear over the regions before TC landfall, resulting in a more rapid intensification of TCs that later approach the coastal areas.

Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature. Social media summary How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.

This study compares the interannual variance of boreal winter near-surface temperature (DJF T2m) with and without performing single model ensemble (SME) in seasonal hindcasts (DEMETER, ENSEMBLES, and NCEP CFSv2) and historical climate simulations (CMIP5). The results demonstrate that the extratropical temperature variability is significantly reduced after performing SME even though the signal in the tropical Pacific remains strong. Cancellation between positive and negative perturbations simulated by individual model members, of both tropical and extratropical origins, leads to the under-simulation. The atmospheric circulation induced by tropical Pacific sea surface temperature is not well represented in global climate models and the simulation is further deteriorated by SME, leading to an unrealistically weak interannual variance of simulated winter temperature in North America. Similar effect was also found in North Eurasia where winter temperature is strongly influenced by atmospheric internal variability and its interaction with land and ice/snow in the middle-high latitudes. The SME procedure should be avoided when evaluating the model performance in simulating the higher-order long-term statistics (such as variance). Variance of individual models should be calculated first and then averaged among members. Models used in seasonal forecast and long-term climate simulation already have good capability in simulating the long-term statistics of stochastic processes in the extratropics, although the capability in accurately simulating the temporal variation is still poor.

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

Cold surges were unusually active in subtropical East Asia during January - February 2005. These cold surges were pre ceded by up stream wave trains, which originated in the Mediterranean-Sahara region and prop a gated east ward along the sub tropical jet stream over the Eurasian continent. The northerly of the upper-level cyclonic anomaly in East Asia coupled with the low-level northerly upon the arrival of wave activity, and this was followed by a quick south ward penetration of cold air mass and surface anticyclone. Diagnostic and numerical results suggest that the anomalously active wave activity affecting the East Asian cold surges may be attributed to an anomalously enhanced jet stream over the Middle East and an anomalously west ward extension of the East Asian Jet Stream. The configuration of these two subtropical jet streams established a strong wave guide through which wave activity forced in the Mediterranean-Sahara region could efficiently prop a gate to East Asia, resulting in above aver age cold surge events in subtropical East Asia. Wave-like perturbation tended to be amplified at the entrance to the East Asian jet through barotropic energy conversion from the mean flow.

This study couples a high-resolution 1-D TKE ocean model (the SIT model) with the Community Atmosphere Model 5.3 (CAM5.3; hereafter CAM5-SIT) configuration, to highlight significant experiments that investigate the influence of different periods of sea surface temperature (SST) feedback, such as 30 minutes, 1, 3, 6, 12, 18, and 30 days, on the Madden-Julian Oscillation (MJO). It substantially breaks through the limitations of flux coupler through air-sea coupling. The aim is to assess the scientific reproducibility and consistency of the findings across different SST feedback cycles in the field of modeling science. Comparing the results to the fifth generation ECMWF reanalysis (ERA5), the high-frequency experiments (C- CTL, C-1day, and C-3days) and low-frequency experiments (C-6days, C-12days, and C-18days) exhibit higher fidelity in capturing various aspects of MJO, except for the C-30days experiment. These aspects in characterizing the basic features of the MJO such as encompass intraseasonal periodicity, eastward propagation, coherence in the MJO band, tilting vertical structure, the lead-lag relationship between MJO related atmosphere and SST variation, phase 2 column-integrated moisture static energy (MSE) tendency, and the projection of all MSE terms onto the MSE tendency of ERA5 across the Maritime Continent (MC). The MJO simulation performance of this study can be assessed in two ways. Firstly, the high-frequency experiments generally capture MJO characteristics, albeit with slightly lower results compared to ERA5 and NOAA data. Secondly, the low-frequency experiments show robust MJO simulations, which can be attributed to the accumulation of energy (temperature) in the upper ocean. This leads to the accumulation of shortwave and longwave radiations, as well as surface heat fluxes from the atmosphere. [ABSTRACT FROM AUTHOR]