Anticyclonic Anomalies Research Articles

The Link between Gulf Stream Precipitation Extremes and European Blocking in General Circulation Models and the Role of Horizontal Resolution

Abstract Past studies show that coupled model biases in European blocking and North Atlantic eddy-driven jet variability decrease as one increases the horizontal resolution in the atmospheric and oceanic model components, but it remains unclear if atmospheric or oceanic resolution plays the greater role, and why. Here, following recent work by Schemm et al., we leverage a large multi-model ensemble to show that a coupled model’s ability to simulate extreme Gulf Stream precipitation is tightly linked to its simulated frequency of European blocking and northern jet excursions. Furthermore, the reduced biases in blocking and jet variability are consistent with better resolved precipitation extrema in high-resolution models. Analysis supports a hypothesis that models which simulate more extreme precipitation can generate more strongly poleward propagating cyclones and more intense anticyclonic anomalies due to the stronger latent heat release occurring during extreme events. By contrast, typical North Atlantic SST biases are found to share only a weak or negligible relationship with blocking and jet biases. Finally, while previous studies have used a comparison between coupled models and models run with prescribed SSTs to argue for the role of ocean resolution, we emphasise here that models run with prescribed SSTs experience greatly reduced precipitation extremes due to their excessive thermal damping, making it unclear if such a comparison is meaningful. Instead, we speculate that most of the reduction in coupled model biases may actually be due to increased atmospheric resolution leading to better resolved convection.

The influence of autumn tropical Atlantic convection, independent of sea surface temperature, on winter Arctic sea-ice variability through teleconnections

Abstract Arctic sea-ice reduction has the potential to cause climatic change and extreme weather in the mid- and high-latitudes of the Northern Hemisphere. The causes of sea-ice variation, such as the influence of tropical sea surface temperature (SST) variation due to El Niño-Southern Oscillation, are actively studied. The notion that tropical SSTs influence atmospheric conditions in mid- and high-latitude regions is widely accepted. Nonetheless, the extent to which SSTs in the eastern tropical Atlantic drive sea-ice variability has not been extensively investigated. Here we show that autumn eastern tropical Atlantic convective cloud activity, independent of underlying SST, influences interannual variation in wintertime sea ice via atmospheric teleconnection with a lag of two months. In years characterized by heightened convective activity in October, Scandinavian anticyclonic anomalies emerge, driven by a wave train originating from the tropical Atlantic. This contrasts with years marked by inactive convection, which may be related to water vapor transport from the African Sahel. These anticyclonic anomalies facilitate the influx of warm, moist air into the Atlantic Arctic, thereby warming SST in the region and impeding the refreezing of sea ice. The convective activity affects not only the interannual variability of sea ice but also the decadal variability. Since convective activity in the tropical Atlantic is not driven by SST, SST may not serve as a reliable predictor for sea-ice forecasting. Clarifying the mechanisms underlying tropical atmospheric convection that are independent of SST is crucial for not only sea-ice forecasting, but also for predicting extreme weather in mid-latitudes.

Interannual Variability of January Haze Pollution in the Sichuan Basin, China and Its Association With the SSTs Over the Southeastern Indian, Tropical Pacific and North Pacific Oceans

ABSTRACTHaze pollution occurs in almost every winter month in the Sichuan Basin, with a higher frequency in January. The interannual and decadal variations of January haze are inconsistent with those in the other winter months, showing a noticeable sub‐seasonal variability in haze pollution. The findings of this study indicate that the noticeably higher haze days over the Sichuan Basin in January are closely associated with the simultaneous sea surface temperature (SST) warming in the North Pacific Ocean (NPO) and tropical Pacific Ocean (TPO), and with the SST cooling in the southeastern Indian Ocean (SIO). When the SST in the NPO warms in January, the negative phase of the Arctic Oscillation is stimulated through a high‐latitude path, the Middle East jet stream weakens, and the Siberian high weakens, and the Aleutian Low intensifies, indicating that cold air activities are restricted and their paths are eastward. This synoptic situation results in weaker cold air over the Sichuan Basin. Meanwhile, the southern branch of the Rossby wave train from the eastern Pacific Ocean propagates along Western Europe to the East Asian coast, leading to high pressure and anticyclonic circulation anomalies over the Sichuan Basin, resulting in reduced precipitation and more haze days in the Sichuan Basin. When the January SST shows warming in the TPO and cooling in the SIO, prominent anticyclonic anomalies strengthen over the Tibetan Plateau and its downstream regions, weakening the southwesterly warm moisture flow. This situation provides unfavourable conditions for precipitation occurrence, thereby facilitating haze pollution over the Sichuan Basin. Consequently, the January SST anomalies in the NPO, TPO and SIO may be associated with the anomalies of local meteorological elements, which restrict the vertical and horizontal dispersion of haze pollution over the Sichuan Basin in January.

Weather systems associated with synoptic variability in the moist margin

Abstract. The moist margin is a sharp gradient of humidity that separates the moist deep tropics from the drier subtropics, and its movement is known to have an important effect on rainfall variability. In this work, we investigate how weather systems are related to synoptic variability in the moist margin. The weather systems considered include convectively coupled equatorial waves and the Madden–Julian Oscillation (MJO), monsoon low-pressure systems (LPSs), and extratropical interactions with the moist margin characterised by upper-level potential vorticity (PV) anomalies. We use an object-based approach in which, first, objects are defined to describe the variability of the moist margin and are then related to weather objects representing the above weather systems. Overall, the results indicate that these weather systems are associated with a large proportion of variability in the moist margin. The MJO and equatorial Rossby waves have a significant modulating effect on the moist margin. In comparison, monsoon LPSs are infrequent but strongly influence the moist margin when they occur. Interactions with the extratropics occur for around one-quarter of moist margin perturbations and display a clear extratropical wave-like signal, often with anticyclonic PV anomalies near the perturbed margin and cyclonic PV anomalies upstream. Overall, moist margin objects associated with weather systems are larger, longer-lived, and precipitate more, highlighting the important role of weather systems.

Comparison of two distinct leading modes in the variability of summer humidex and temperature heatwaves over North America

Continuous hot and humid conditions pose greater health risks than heat alone, making it crucial to distinguish between temperature-driven and humidity-amplified heat stress. The variability of monthly humidex and temperature heatwaves over North America (NA) is compared for extended summers (June-September) from 1951 to 2022. Two distinct leading modes are identified for both humidex and temperature heatwaves over NA using empirical orthogonal function (EOF) analysis, collectively explaining 31% and 27% of total variance, respectively. These two leading modes, exhibiting a phase shift due to their orthogonality, are associated with large-scale atmospheric wave trains extending from the North Pacific to NA. This results in atmospheric pressure anomalies across the continent, driving notable differences in the variability of both heatwaves over NA. Atmospheric moisture transported from the North Pacific to NA also affects the development of both heatwaves, with more pronounced moisture anomalies observed for humidex heatwaves, highlighting a key distinction in the large-scale atmospheric circulation between humidex and temperature heatwaves. Positive phases of both heatwaves are associated with an anticyclonic anomaly, which leads to anomalous descent, reduced total cloud cover, above-normal surface radiation heating, and below-normal surface relative humidity over NA. Atmospheric moisture acts as a greenhouse gas to absorb longwave radiation, leading to increased downward longwave radiation. However, these physical processes exhibit weaker feedback with humidex heatwave variability across the two distinct modes, indicating the complexity of these interactions involving intensified cloud cover, surface humidity, and latent heat release due to significant atmospheric moisture injected into the regions of NA.

Serial Clustering of Tibetan Plateau Vortices and Its Relationship With Atmospheric Quasi‐Biweekly Oscillation Revealed by a Database Derived From Multiple Reanalysis

AbstractTibetan Plateau vortices (TPVs) are the major precipitation‐producing weather system, which dominates the water supplies over the TP. Serial clustering is one of the basic features of TPVs and is closely related to the atmospheric intraseasonal oscillation of the TP. Through a database of TPVs derived from multiple reanalysis data sets, we investigated the spatiotemporal characteristics of TPV clustering (TPVC) and its connection with the atmospheric quasi‐biweekly oscillation (QBWO). The TPV tracks from variant reanalysis data sets reproduced consistent features for TPVC. The database revealed that the TPVC primarily occurs during the warm season and exhibits significant interannual variability. TPV clustering frequently occurs during the positive phase of the QBWO, in which the TP emerges cyclonic anomalies at lower atmospheric levels and anticyclonic anomalies at upper levels. This configuration creates a baroclinic structure that favors the formation of TPVCs. Conversely, the negative phase of QBWO results in an inverse atmospheric anomaly pattern, reducing TPVC occurrences. The interannual variability of TPVCs is primarily influenced by the amplitude of relative vorticity rather than the frequency of positive or negative phases. Furthermore, there are distinct differences in circulation patterns between years with high and low TPVC frequencies. In high‐TPVC (low‐TPVC) years, the lower levels of the TP predominantly show positive (negative) vorticity anomalies, accompanied by an anticyclone (cyclone) in the northern TP and a cyclone (anticyclone) in the eastern TP, while an anti‐cyclonic (cyclonic) anomaly is active over the TP that indicates an intensified (weakened) South Asian High.

Observed Warming and Weakening of the Philippine Sea Deep Circulation Over the Past Decade

AbstractDeep circulation in the Philippine Sea, an important component of the deep limb of the Pacific Meridional Overturning Circulation, redistributes heat and carbon, as the circulation carries cold dense water originating from Antarctic bottom water (AABW). On the basis of hydrographic observations, the water mass properties and circulation in the deep Philippine Sea were investigated. The cold water entering the deep Philippine Sea through the Yap‐Mariana Junction gradually warms as it invades the interior of the deep basin, and the intrusion path exhibits a cyclonic structure. From 2015 to 2023, deep water in the Philippine Basin warmed by 0.18 ± 0.20 × 10−3 °C yr−1 below 4,000 m, featuring the deepening of potential temperature isotherms due to the continued loss of cold water. Further analyses of the satellite‐observed ocean bottom pressure data revealed anticyclonic anomalies in the deep currents, indicating a weakening of the deep circulation in the Philippine Sea. Warming of the deep water and weakening of the deep circulation both imply a contraction of cold dense water entering the deep Philippine Sea, which is believed to be relevant to the reduced formation rates of AABW.

Anthropogenic intensification of Arctic anticyclonic circulation.

The past four decades have witnessed a strengthening of the winter anticyclonic circulation over the Barents-Kara Sea (BKS), a change that has contributed substantially to amplified local warming and sea ice loss, as well as to Eurasian cooling. However, the cause of this trend in the BKS atmospheric circulation remains unknown. Here we show that anthropogenic greenhouse gases are the primary driver of the strengthening of the BKS anticyclonic circulation, with anthropogenic aerosols playing a secondary role, both together accounting for about 86% of the observed circulation trend. Both forcings induce an amplified BKS low-tropospheric warming through coupling with strong sea ice loss. This amplified warming raises geopotential height aloft through thermal expansion, causing an anomalous anticyclonic anomaly, which in turn enhances warming and sea ice loss, forming a positive feedback loop. Our work provides a theoretical framework for understanding Arctic atmospheric circulation responses to anthropogenic warming and may have implications for climate and environment in the Arctic and beyond.

Emerging Interannual Variability of Compound Heat Waves over the Yangtze River Valley since 2000

Abstract The variability of daytime–nighttime compound heat waves (CHWs) is a highly concerning issue due to severe impacts on human and natural systems. Although several studies surveyed physical processes for the CHW occurrence, its interannual variability and associated mechanisms have not been well understood. Focusing on CHWs in the Yangtze River valley (YRV, a hotspot across China), this paper indicates an emergence of enlarged interannual variability after entering into the twenty-first century, before which the interannual variability was quite small. The possible mechanism underlying the high interannual variability is further explored in terms of atmospheric and oceanic backgrounds. The results show that the atmospheric background associated with higher-than-normal CHWs over the YRV features anticyclonic circulation anomalies tilting southeastward from the north of the YRV in the upper troposphere to the western Pacific in the lower troposphere. Accordingly, the upper-tropospheric easterly and lower-tropospheric southwesterly anomalies dominate the YRV, causing anomalous subsidence and increased humidity in situ, respectively, which benefit the increase in CHWs. The tripole (positive–negative–positive) sea surface temperature (SST) anomalies in the North Atlantic (NA) and the positive SST anomalies in the Maritime Continent (MC) also play roles in increasing the YRV CHWs by influencing the above atmospheric circulations. The NA tripole SST anomalies tend to affect the upper- and midtropospheric anticyclonic anomalies through the eastward-propagating wave train across Eurasia. The warming of the MC SSTs can impact the lower-tropospheric anticyclonic anomaly over the western Pacific via local meridional circulation. The opposite situations are applicable for decreased CHWs over the YRV. Significance Statement Daytime–nighttime compound heat waves (CHWs) refer to persistent processes with abnormally high temperatures occurring both in daytime and nighttime. Compared with heat waves (HWs) occurring only at daytime or nighttime, the CHWs exert more severe damage to natural ecosystems and human society. Thus, understanding the physical mechanisms of CHWs is urgently needed. This study examines the interannual variability of Yangtze River valley (YRV) CHWs and finds that it exhibits a pronounced enlargement after 2000. During this period, an anomalous anticyclone tilting southeastward from the north of the YRV in the upper level to the western Pacific in the lower level is a favorable atmospheric circulation background for the increase in CHWs over the YRV, and vice versa. Sea surface temperatures (SSTs) in the North Atlantic (NA) and the Maritime Continent (MC) also play important roles. The positive–negative–positive SST anomalies in the NA and the warming SSTs in the MC tend to increase the YRV CHWs, through their influences on CHW-related atmospheric circulations in the upper troposphere and lower troposphere, respectively. These findings are expected to deepen our understanding of CHW variability, which are of great importance for disaster prevention and mitigation.

Interdecadal Variation of Springtime Compound Temperature‐Precipitation Extreme Events in China and Its Association With Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation

AbstractThe concurrent occurrence of temperature and precipitation extremes, known as compound temperature‐precipitation extreme events (CTPEEs), leads to more pronounced consequences for human society and ecosystems than when these extremes occur separately. However, such compound extremes have not been sufficiently studied, especially during boreal spring. Spring is an important transition season, during which the CTPEEs plays a pivotal role in plant growth and revival of terrestrial ecosystems. This study investigates the spatio‐temporal variation characteristics of spring CTPEEs in China, including warm‐dry, warm‐wet, cold‐dry, and cold‐wet combinations. The compound cold‐wet extreme events occur most frequently, followed by warm‐dry, warm‐wet, and cold‐dry events. The frequency of CTPEEs associated with warm (cold) extremes shows a marked interdecadal increase (decrease) around the mid‐to‐late 1990s. It is found that the interdecadal change in CTPEEs is primarily determined by the variation in temperature extremes. This interdecadal shift coincides with the phase transitions of the Atlantic Multidecadal Oscillation (AMO) and the Interdecadal Pacific Oscillation (IPO). After the mid‐to‐late 1990s, the configuration of a positive AMO and a negative IPO excited atmospheric wave trains over mid‐high latitudes, causing high‐pressure and anticyclonic anomalies over East Asia. This leads to less cloudiness, allowing an increase in downward solar radiation, which enhances surface warming and contributes to an increase (decrease) in warm‐dry and warm‐wet extremes. The above observations are confirmed by the Pacemaker experiments. The results of this study highlight a significant contribution of internal climate variability to interdecadal changes in CTPEEs at the regional scale.

Association of spring thermal forcing anomalies in the Tibetan Plateau with dust aerosol changes over the Taklamakan Desert.

Association of spring thermal forcing anomalies in the Tibetan Plateau with dust aerosol changes over the Taklamakan Desert.

Enhanced Influence of Late‐Winter Arctic Oscillation on Early Spring Temperature in North and Northeast Asia

AbstractNumerous studies have highlighted the simultaneous relationship between the Arctic Oscillation (AO) and weather/climate in Asia. However, the stability of the precursor signals in AO for Asian surface air temperature (SAT), which is important for short‐term climate prediction, has received little attention. In this study, a strengthened relationship is identified between the late‐winter AO and the early spring SAT over North and Northeast Asia (NNA) around the 1990s. During 1990–2022, a positive (negative) phase of AO during late winter is generally followed by significant warming (cooling) anomalies in the NNA during early spring, whereas this relationship is insignificant during 1961–1987. Further result shows a good persistence of the late‐winter AO to early spring after the 1990s. Accordingly, the AO exerts a strengthened impact on Mongolian anticyclone and Asian westerly anomalies through modulation of a Rossby wave train that propagates from the Arctic to the NNA in early spring, leading to significant SAT anomalies at NNA. Additionally, the AO‐related temperature anomalies intensified in the stratosphere after the 1990s, linking AO and stratospheric polar vortex (SPV). The intensified (weakened) SPV following positive (negative) AO facilitates warming (cooling) anomalies at NNA via downward‐propagating Eliassen‐Palm fluxes at wave number 1 and circumpolar westerlies in middle and lower troposphere. The seasonal persistence of AO and the strengthened relationship between AO and SPV synergistically enhance the influence of late‐winter AO on early spring SAT in the NNA, which might be attributed to the interdecadal changes in background circulation over the Arctic.

Atlantic Meridional Overturning Circulation slowdown modulates wind-driven circulations in a warmer climate

Wind-driven and thermohaline circulations, two major components of global large-scale ocean circulations, are intrinsically related. As part of the thermohaline circulation, the Atlantic Meridional Overturning Circulation has been observed and is expected to decline over the twenty-first century, potentially modulating global wind-driven circulation. Here we perform coupled climate model experiments with either a slow or steady Atlantic overturning under anthropogenic warming to segregate its effect on wind-driven circulation. We find that the weakened Atlantic overturning generates anticyclonic surface wind anomalies over the subpolar North Atlantic to decelerate the gyre circulation there. Fingerprints of overturning slowdown are evident on Atlantic western boundary currents, encompassing a weaker northward Gulf Stream and Guiana Current and a stronger southward Brazil Current. Beyond the Atlantic, the weakened Atlantic overturning causes a poleward displacement of Southern Hemisphere surface westerly winds by changing meridional gradients of atmospheric temperature, leading to poleward shifts of the Antarctic Circumpolar Current and Southern Ocean meridional overturning circulations.

Role of the Europe–China Pattern Teleconnection in the Interdecadal Autumn Dry–Wet Fluctuations in Central China

Based on statistical analyses of long-term reanalysis data, we have investigated the interdecadal variations of autumn precipitation in central China (APC-d) and the associated atmospheric teleconnection. It reveals that the increased autumn rainfall in central China during the last decade is a portion of the APC-d, which exhibits a high correlation coefficient of 0.7 with the interdecadal variations of the Europe–China pattern (EC-d pattern) teleconnection. The EC-d pattern teleconnection presents in a “+-+” structure over Eurasia, putting central China into the periphery of a quasi-barotropic anticyclonic high-pressure anomaly. Driven by positive vorticity advection and the inflow of warmer and moist air from the south, central China experiences enhanced ascending motion and abundant water vapor supply, resulting in increased rainfall. Further analysis suggests that the EC-d pattern originates from the exit of the North Atlantic jet and propagates eastward. It is captured by the Asian westerly jet stream and proceeds towards East Asia through the wave–mean flow interaction. The wave train acquires effective potential energy from the mean flow by the baroclinic energy conversion and simultaneously obtains kinetic energy from the basic westerly jet zones across the North Atlantic and the East Asian coasts. The interdecadal variation of the mid-latitude North Atlantic sea surface temperature (MAT-d) exhibits a significant negative relationship with EC-d, serving as a modulating factor for the EC-d pattern teleconnection. Experiments with CMIP6 models predict that the interdecadal variations in APC-d, EC-d, and MAT-d will maintain stable high correlations for the rest of the 21st century. These findings may contribute to forecasting the interdecadal autumn dry–wet conditions in central China.

Intensified Western Pacific Convection Increases the Probability of Hot Extremes in the Middle East During the Boreal Spring

AbstractUnder global warming, the convective heating over the western Pacific (WP) has exhibited a significantly intensifying trend during the boreal spring, while the surface air temperatures in the Middle East (ME) have increased more rapidly than those in other tropical regions. Are these climate phenomena of the two regions physically connected? If yes, what are the responsible dynamical mechanisms involved? Utilizing the ERA5 reanalysis data and model simulations, this study reveals a significant seesaw variation in the convection and temperature trends between WP and ME. When convective heating intensifies over the WP, the ME tends to be drier and hotter during the spring, and vice versa. A further investigation indicates that the enhanced WP convective heating can induce anticyclonic circulation anomalies in the upper and middle troposphere over the Iranian and Tibetan plateaus. These anomalous high pressures extend westward, exhibiting a barotropic structure, which leads to stronger sinking motions, reduced cloud cover, and increased surface solar radiation over the ME. Consequently, these conditions result in drier and hotter soils and an increase in heatwave days in the ME. This study provides useful information for enhancing our understanding of the role of tropical WP climate change in influencing the upstream climate conditions with a focus on the ME.

Reduction in Arctic sea ice amplifies the warming of the northern Indian Ocean

Reduction in Arctic sea ice amplifies the warming of the northern Indian Ocean

Using rare event algorithms to understand the statistics and dynamics of extreme heatwave seasons in South Asia

Abstract Computing the return times of extreme events and assessing the impact of climate change on such return times is fundamental to extreme event attribution studies. However, the rarity of such events in the observational record makes this task a challenging one, even more so for ‘record-shattering’ events that have not been previously observed at all. While climate models could be used to simulate such extremely rare events, such an approach entails a huge computational cost: gathering robust statistics for events with return time of centuries would require a few thousand years of simulation. In this study, we use an innovative tool, rare event algorithm, that allows us to sample numerous extremely rare events at a much lower cost than direct simulations. We employ the algorithm to sample extreme heatwave seasons, corresponding to large anomalies of the seasonal average temperature, in a heatwave hotspot of South Asia using the global climate model Plasim. We show that the algorithm estimates the return levels of extremely rare events with much greater precision than traditional statistical fits. It also enables the computation of various composite statistics, whose accuracy is demonstrated through comparison with a very long control run. In particular, our results reveal that extreme heatwave seasons are associated with an anticyclonic anomaly embedded within a large-scale hemispheric quasi-stationary wave-pattern. Additionally, the algorithm accurately represents the intensity-duration-frequency statistics of sub-seasonal heatwaves, offering insights into both seasonal and sub-seasonal aspects of extreme heatwave seasons. This innovative approach could be used in extreme event attribution studies to better constrain the changes in an event’s probability and intensity with global warming, particularly for events with return times spanning centuries or millennia.

Effects of Anthropogenic Aerosols on the East Asian Winter Monsoon

AbstractCirculation patterns linked to the East Asian winter monsoon (EAWM) affect precipitation, surface temperature, and air quality extremes over East Asia. These circulation patterns can in turn be influenced by aerosol radiative and microphysical effects through diabatic heating and its impacts on atmospheric vorticity. Using global model simulations, we investigate the effects of anthropogenic aerosol emissions and concentration changes on the intensity and variability of the EAWM. Comparison with reanalysis products indicates that the model captures the mean state of the EAWM well. The experiments indicate that anthropogenic aerosol emissions strengthen the Siberian High but weaken the East Asian jet stream, making the land areas of East Asia colder, drier, and snowier. Aerosols reduce mean surface air temperatures by approximately C, comparable to about half of the difference between strong and weak EAWM episodes in the control simulation. The mechanisms behind these changes are evaluated by analyzing differences in the potential vorticity budget. Anthropogenic aerosol effects on diabatic heating strengthen anomalous subsidence over southern East Asia, establishing an anticyclonic circulation anomaly that suppresses deep convection and precipitation. Aerosol effects on cloud cover and cloud longwave radiative heating weaken stability over the eastern flank of the Tibetan Plateau, intensifying upslope flow along the western side of the anticyclone. Both circulation anomalies contribute to reducing surface air temperatures through regional impacts on thermal advection and the atmospheric radiative balance.

An Increase in Autumn Marine Heatwaves Caused by the Indian Ocean Dipole in the Bay of Bengal

Abstract This study investigates the interannual variability of marine heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection + entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63% and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of −20% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, El Niño–Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.

Moisture dynamic processes of the westward propagation of quasi-biweekly oscillation in Asian tropical summer monsoon rainfall

Moisture dynamic processes of the westward propagation of quasi-biweekly oscillation in Asian tropical summer monsoon rainfall