Vapor Convergence Research Articles

A Numerical Simulation of a Fog Event in the Sichuan Basin, China: The Sensitivity to Terrain Elevations

In this paper, we utilize the Advanced Research version of the Weather Research and Forecasting model (ARWv4) to explore how the fog is affected by the basin’s topography during a radiation fog event in the Sichuan Basin in December 2016 by setting up three sets of terrain tests. The simulation results demonstrate that the fog area in the expanded basin terrain emerges 40 min earlier than in the original topography control test (CTL), with the fog area extent marginally reduced. Conversely, the fog area in the reduced basin terrain emerges one hour earlier than in the CTL, with the fog area extent increased by 133.5%. Basin topography is an essential factor influencing the humidity, temperature, and dynamical fields. The expansion of basin topography was shown to be unfavorable for water vapor convergence. Moreover, the area exhibiting relative humidity levels exceeding 95% at the peak of the fog intensity was smaller than that observed in CTL. The impact of radiative cooling was diminished, and the thickness and intensity of the inversion layer were reduced compared to CTL. In addition, the wind speed in the marginal area exceeded 5 m s−1, and the fog formation was observed only in the central portion of the basin, where wind speeds ranged from 0 to 3 m s−1. In contrast, the change in the topography of the narrowed basin resulted in the opposite phenomenon overall. This work emphasizes the importance of basin topography in forming and developing the fog in the Sichuan Basin.

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and anomalous negative geopotential height at 500 hPa and anomalous cyclone at 700 hPa control the entire Tarim Basin, favoring anomalous upward motion, and western and southwestern water vapor transport. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, the western part of the Tarim Basin is affected by the anomalous cyclone while the eastern part is affected by the amomalous anticyclone, leading to the east-west discrepancy. The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

How Does the East Siberian Sea Ice Affect the June Drought Over Northwest China After 2000?

AbstractChanges in Arctic sea ice have exerted remarkably effects on the Eurasian climates, but it is unclear whether Arctic sea ice also contributes to Northwest China's ongoing summer drought. This study investigates the influence of the interannual variability of Arctic sea ice on the June drought in Northwest China from 1979 to 2021. It reveals that the early‐autumn sea ice in the East Siberian Sea is correlated with drought conditions in June in Northwest China, with a more pronounced connection during the period of 2000/2001–2020/2021 (P2) compared to 1979/1980–1999/2000 (P1). Mitigated drought in Northwest China is associated with anomalously high sea ice concentration (SIC) in the East Siberian Sea. Further analysis suggests that the strengthened link may be due to greater SIC variability in the East Siberian Sea during P2 than P1. In P2, positive early‐autumn SIC anomaly is linked to anomalous northeasterly winds, promoting drier soil and widespread cooling in the East European Plain. This dry soil signal may persist into the ensuing spring and early summer, inducing an anticyclonic circulation anomaly over Siberia, which could facilitate the water vapor convergence in Northwest China, thereby enhancing humidity conditions in the region. The insights from this study could offer valuable information for improved prediction of droughts in Northwest China.

A high‐resolution climatological study of explosive cyclones in the Mediterranean region: Frequency, intensity and synoptic drivers

AbstractIn the complex context of climate change and in a heavily populated area like the Mediterranean region, understanding and studying explosive cyclones (ECs) is crucial because of their potential to cause extreme weather events, including strong winds, heavy rainfall, and significant disruptions to human activities and infrastructure, as happened in 2018 with the Vaia storm. The genesis and persistence of ECs, characterized by a rapid drop in central mean sea level pressure exceeding 12 hPa in 12 hours, are influenced by various physical processes and while water vapour convergence in the mid‐low troposphere is crucial, mid‐upper tropospheric cyclonic vorticity advection and upper tropospheric divergence also play significant roles. In this study, we used ERA5 hourly data of mean sea level pressure from 1979 to 2020 to analyse EC occurrences in the Mediterranean. The identification of EC events followed the 12‐hr deepening‐rate criterion introduced by Zhang et al. (2017), as shorter deepening rates definitions proved unreliable. A total of 80 ECs were identified and classified based on their spatial occurrence and magnitude, 34 of which were concentrated in the northwest of the basin, likely due to orographic deformation caused by the Alps on baroclinic waves originating from the Atlantic. The study also identified recurring synoptic patterns associated with the persistence of ECs over the sea, including the presence of potential vorticity (PV) streamers and mid‐tropospheric dry‐air intrusions. Empirical Orthogonal Function (EOF) analysis highlighted the Scandinavian pattern as the primary driver, with blocking conditions over western Russia and Scandinavia, and composite analyses revealed the intrusion of PV to various atmospheric levels, extending up to 500 hPa. In summary, this study offers valuable insights into the complex mechanisms governing EC formation in the Mediterranean Basin, shedding light on the synoptic patterns, atmospheric dynamics, and potential impacts on regional weather systems.

Diagnosis of Atmospheric Processes from a Local Perspective for the Western North Pacific Summer Monsoon Onset

Abstract The climatological western North Pacific summer monsoon onset, a so-called convection jump, occurs around the 41st pentad, corresponding to an abrupt northeastward extension of strong convection. This study investigates the process of convection jump from a local perspective. Composite analyses are performed based on the onset dates that are identified in individual years. The results show that the convective inhibition (CIN) decreases dramatically around the onset dates, while the convective available potential energy (CAPE) reaches its maximum long before the onset, suggesting that the CIN, rather than CAPE, plays a dominant role in triggering convection. Further analysis indicates that the reduction of CIN is induced by the increased low-level relative humidity, which is the result of enhanced water vapor convergence. The moisture transportation is primarily contributed by the wind transfer from easterlies to southeasterlies or southerlies along the southern boundary of the convection jump region, in accordance with the monsoon trough establishment. The present observational results may be used to evaluate climate models in simulating the stepwise evolution of summer monsoon. Significance Statement The convection jump refers to rapid convection extension to the northeastern part of the Philippines Sea in late July and corresponds to the deepening of the monsoon trough and northward shift of the western North Pacific subtropical high. Therefore, the convection jump has important impacts on the East Asian summer monsoon. The crucial role of transient atmospheric adjustment in triggering the convection jump has been shown in previous studies. However, the reason for the temporal preference of convection jump remains unknown. This study further specifies the process of atmospheric adjustments around the convection jump from a local perspective and reveals that the transition from the easterlies to southeasterlies or southerlies decreases convective inhibition and thus favors the convection jump. The present results can be used to diagnose the ability of climate models to simulate the stepwise evolution of Asian–Pacific summer monsoon.

Influence of autumn soil moisture over Kalimantan Island on following winter precipitation over southern China

AbstractThe atmospheric activity on Kalimantan Island (KI) is important for regulating regional weather and climate. This study investigates the effect of autumn soil moisture over KI on following winter precipitation over southern China (SC) during 1968–2014. The results show that the autumn soil moisture over the KI has a significant negative correlation with subsequent winter precipitation over SC. The correlation remains statistically significant when using partial correlation to filter out the concurrent influences of El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) signals. The soil moisture anomalies over KI, which initiate in the autumn and persist into the winter, lead to changes in local thermal conditions and atmospheric temperature. Negative soil moisture anomalies over KI will result in positive heating anomalies of the atmosphere above the land surface. This atmospheric heating causes ascending motion, which creates a semi‐closed vertical circulation from KI to the tropical northwest Pacific. This vertical circulation would strengthen the northwest Pacific anticyclone and weaken the East Asian winter monsoon (EAWM). Consequently, southwesterly water vapour flux prevails in the SC as well as the South China Sea (SCS), facilitating the transportation of more water vapour into the SC. Simultaneously, water vapour convergence in the SC. Collectively, these contribute to an addition of precipitation over SC.

Comparative analysis of heavy rainfall area between landfalling typhoon LUPIT (2109) and typhoon LISA (9610)

Based on the ERA5 reanalysis data and the surface observations from automatic weather stations, a comparative analysis has been conducted to investigate the differences in heavy rainfall distributions caused by two landfalling tropical cyclones (TCs): LUPIT (2109) and LISA (9610). The two TCs have similar tracks, intensity and landing points, but show different asymmetric features in their rainstorm location relative to their tracks. The results indicate that the TC rainfall differences are mainly caused by different rainstorm formation mechanisms. The wind shear contributes most to the rainstorm of LISA, while land-sea contrast and topographical effect are the main factors of LUPIT rainstorm. Under the influence of strong environmental vertical wind shear and the weak cold air invasion from the west, the circulation center of LISA tilts westward with height, which cooperates with the low-level water vapor convergence and vertical ascending movement on the western side of the TC center to jointly cause the heavy rainstorm to the west of LISA center. In contrast, LUPIT has weak environmental vertical wind shear and no obvious structure tilting with height. Topographic effect plays a crucial role in causing the heavy rainstorm on the north of TC center. The southeasterly jet is blocked by the Taimu Mountain in the northeastern Fujian Province, and the strong ascending motion caused by the terrain-induced convergence appears to the north of LUPIT center. In addition, the moisture convergence is more pronounced in the north and weaker in the south. The intrusion of weak cold air from the east to the coastal areas of central-northern Fujian, and the moisture-convergence distribution, jointly cause the heavy rainstorm to the north of LUPIT.

Potential Impacts of Future Climate Change on Super-Typhoons in the Western North Pacific: Cloud-Resolving Case Studies Using Pseudo-Global Warming Experiments

Potential impacts of projected long-term climate change toward the end of the 21st century on rainfall and peak intensity of six super-typhoons in the western North Pacific (WNP) are assessed using a cloud-resolving model (CRM) and the pseudo-global warming (PGW) method, under two representative concentration pathway (RCP) emission scenarios of RCP4.5 and RCP8.5. Linear long-term trends in June–October are calculated from 38 Coupled Model Intercomparison Project phase 5 (CMIP5) models from 1981–2000 to 2081–2100, with warmings of about 3 °C in sea surface temperature, 4 °C in air temperature in the lower troposphere, and increases of 20% in moisture in RCP8.5. The changes in RCP4.5 are about half the amounts. For each typhoon, three experiments are carried out: a control run (CTL) using analysis data as initial and boundary conditions (IC/BCs), and two future runs with the trend added to the IC/BCs, one for RCP4.5 and the other for RCP8.5, respectively. Their results are compared for potential impacts of climate change. In future scenarios, all six typhoons produce more rain rather consistently, by around 10% in RCP4.5 and 20% in RCP8.5 inside 200–250 km from the center, with increased variability toward larger radii. Such increases are tested to be highly significant and can be largely explained by the increased moisture and water vapor convergence in future scenarios. However, using this method, the results on peak intensity are mixed and inconsistent, with the majority of cases becoming somewhat weaker in future runs. It is believed that in the procedure to determine the best initial time for CTL, which yielded the strongest TC, often within a few hPa in minimum central sea-level pressure to the best track data, an advantage was introduced to the CTL unintentionally. Once the long-term trends were added in future runs, the environment of the storm was altered and became not as favorable for subsequent intensification. Thus, the PGW approach may have some bias in assessing the peak intensity of such super-typhoon cases, and caution should be practiced.

Recent trends and variability of temperature and atmospheric water vapor over South Asia

This study examines the recent trends and variability of temperature and atmospheric water vapor over South Asia during the summer monsoon season from 1970 to 2022. We employ gridded reanalysis and observational datasets to assess the trends and variability in surface temperature and further investigate the associated physical processes. Our results show that the surface temperature over South Asia has increased by 0.5 °C per decade. Notably, we find a statistically significant major transition in the surface temperature series in 1995, such that 1970–1994 (1995–2022) is associated with anomalous cooling (anomalous warming). Since 1995, not only have the temporal variations in regional surface temperature, atmospheric water vapor, and clear-sky downward longwave radiation been synchronous at interannual scales, but their largest spatial variations have been located mainly over the same region. A diagnosis of the atmospheric moisture budget reveals that the observed changes in water vapor convergence over South Asia are dominated by changes in mean circulation dynamics, while the change in thermodynamics is relatively small. The enhancement of the Somali low-level jet may contribute to increased water vapor in South Asia by modulating low-level circulations.

Distribution Characteristics of the Short-term Heavy Rainfall of an MCC in Shandong Province

This study employs a comprehensive approach, utilizing conventional meteorological observation data, Fengyun satellite cloud imagery, and ERA5 reanalysis data to examine a short-term heavy rainfall event and its underlying causes in Shandong Province from August 14 to 16, 2020. The findings reveal that: (1) This event represents a typical Mesoscale Convective Complex (MCC)-induced rainfall process, with the primary precipitation zone in central and southern Shandong. The most intense hourly rainfall is observed along the side of the MCC with the steepest Tropical Brightness Temperature Blackbody (TBB) gradient. The heaviest hourly rainfall happens right around the time of the lowest TBB interval. (2) The rainfall event is marked by a vertical atmospheric structure with a high-altitude westerly jet and a low-level southwest jet, which makes it easy for water vapour to move and shear lines to form. Favourable conditions for water vapour convergence and high specific humidity are noted. During episodes of heavy precipitation, there is a marked upward motion in the lower troposphere, aligning with the vertical pattern of low-level convergence and high-level divergence.

Anomalous Characteristics of Water Vapor Budget on the Tibetan Plateau under the Influence of Tropical Cyclones over the Bay of Bengal during Early Summer

Abstract Early summer is a peak time for tropical cyclone (TC) activities over the Bay of Bengal (BoB) and a period of South Asian monsoon onset, and the TCs during this time have a significant impact on the water vapor transport associated with monsoons. This study investigates the anomalous characteristics of the dynamic–thermal atmospheric circulation structure and water vapor budget over the Tibetan Plateau (TP) under the influence of BoB TCs generated in May from 1979 to 2020 with JTWC best track data and ERA5 data. Results reveal that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. A part of the water vapor is transported directly to the TP by deep southerly jet, while the other part is lifted by TCs and then climbs upward to the TP by two uplift processes occurring on the southern slope of the TP and over the TP respectively, which makes the whole troposphere over the southeastern TP warmer and wetter. It is found that anomalous southeasterly airflow in the northeast of TC circulation turns to anomalous southwesterly airflow forming an abnormal anticyclonic circulation over the southern TP in the middle and upper troposphere due to the diabatic heating effect. In this process, the TP acts as an anomalous water vapor sink with remarkable water vapor inflow through its southern boundary, with the main water vapor outflow through the eastern boundary, but a weak easterly water vapor backflow to the eastern TP in the lower troposphere. Significance Statement This study attempts to investigate the anomalous features of the water vapor budget over the Tibetan Plateau (TP) under the influence of the Bay of Bengal (BoB) tropical cyclones (TCs) during early summer. Results show that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. The TP acts as an anomalous water vapor sink with more and higher water vapor inflows through the southern boundary of the TP. A positive temperature and humidity anomaly can be found over the southeastern TP extending upward into the middle and upper troposphere. The results are helpful to understand how the BoB TCs affect the weather process over the TP.

Influence of the Southern Indian Ocean Dipole on the following spring climate in China: A synthetic observational and numerical study

The influence of the Southern Indian Ocean Dipole (SIOD) on the following spring climate in China is examined, using a 42-year simulation of the Community Earth System Model, version 1.0.4 (CESM1.0.4) and 42-year observation-based ocean-atmosphere analyses (1979–2021). It is shown that the SIOD, an inverse phase pattern of SST anomalies (SSTAs) in the southwest and northeast of the Southern Indian Ocean (SIO), is the dominant mode of observed interannual variability. Composite analyses based on observational data suggest that when a positive SIOD signal occurs, the surface temperature in the ensuing spring is warmer in southwest China and colder in northeast China, and the precipitation in southeast China decreases significantly. The response phase of the surface temperature and precipitation in China under a negative SIOD signal is the opposite of that under a positive SIOD signal, and the response intensity is also greater under a negative SIOD signal. Numerical experiments with CESM can also well reproduce the distribution of the surface temperature and precipitation the following spring over China under positive and negative SIOD signals, respectively. Analysis of the mechanism by which the SIOD influences the subsequent precipitation in China shows that it may occur through interaction between the mid to high latitudes and low latitudes, as well as upper and lower tropospheric circulations. During negative SIOD years, due to the remote response generated by the boreal winter SSTA in the SIO, a strong positive anomaly at 500 hPa geopotential height extending from northeast China to the northwest Pacific Ocean at mid to high latitudes corresponds to a significant low pressure in south and northwest China, and this low pressure helps southerly winds bring more water vapor to southeast China. Meanwhile, the westward extension and northward elevation of the western Pacific subtropical high lead to the convergence of water vapor in south China. In addition, westerly anomalies over the equatorial Indian Ocean and easterly anomalies over the equatorial western Pacific change the local Walker circulation, which weakens the northwest Pacific anticyclonic circulation and subtropical westerly jet. The abnormally warm SST in the southern equatorial Indian Ocean promotes the formation of the Hadley circulation, enhances the upward movement, and changes the water vapor convergence in south China. These factors together lead to an increase in precipitation in southeast China in the following spring in both observations and CESM numerical experiments. At the same time, during positive SIOD years, both observations and simulations show that the causes affecting precipitation are almost the opposite of those in negative SIOD years. Therefore, the SIOD during boreal winter can be an important predictor of precipitation variability over south and southeast China during the following spring.

An interdecadal change in the relationship between May North Atlantic oscillation and early summer precipitation over the Eastern Tibetan Plateau around the late 1990s

Based on the observational and reanalysis datasets, a dipole pattern of the early summer (June) precipitation over the eastern Tibetan Plateau (TP) is identified through empirical orthogonal function. In contrast to previous researches, this paper introduces the May North Atlantic Oscillation (NAO) as a preceding signal and investigates its connection with subsequent early summer precipitation over the eastern TP during 1980–2019, focusing on predictive aspects. Results reveal that the correlation between NAO and primary eastern TP precipitation pattern (Precip_EOF1) has weakened since 2000. During 1980–2000, an equivalent barotropic Silk Road Pattern (SRP) observed across Eurasia triggers southerly wind anomalies over the TP. This, in turn, leads to the northward shift of the water vapor, which favors the ascending motion over the northern TP (NTP) due to water vapor convergence. Additionally, the SRP-related sensible heating also plays a critical role in vertical motion over the eastern TP by enhancing the TP thermal effect. Consequently, these factors contribute to shaping the dipole pattern of eastern TP precipitation. However, the weakened relationship between NAO and Precip_EOF1 during 2001–2019 is attributed to the absence of NAO-related atmospheric circulation over Eurasia. Further analysis suggests that these circulation anomalies arise from the interdecadal variability of the NAO and its phase shift. Moreover, when the influence of sea surface temperature anomalies over the northern North Atlantic is removed, the correlation of Precip_EOF1 with NAO and Atlantic Multidecadal Oscillation (AMO) both become insignificant. This suggests that the NAO-related dipole pattern of eastern TP precipitation is modulated by preceding northern North Atlantic sea surface temperature rather than AMO on the interdecadal timescale.

Anthropogenic warming induced intensification of summer monsoon frontal precipitation over East Asia.

Summer monsoon frontal rainfall in East Asia (EA) is crucial for water resources and flood hazards in densely populated areas. Recent studies have documented the increasing intensity of summer frontal rainfall over recent decades. However, the extent of ongoing climate change on the intensification of the EA frontal precipitation system remains uncertain. Using an objective method for detecting frontal systems, we found a 17 ± 3% increase in observed frontal rainfall intensity during 1958 to 2015. Climate model simulations with and without greenhouse gases suggest that anthropogenic warming plays a key role in the intensification of EA summer frontal precipitation by 5.8% from 1991 to 2015. The analysis highlights that enhanced water vapor convergence and reinforced western North Pacific subtropical High collectively increased moisture transport to the region, resulting in intensified EA frontal precipitation. The results lend support to the anthropogenic warming-induced enhancement of the EA frontal precipitation and its persistence in the future.

Enhanced atmospheric water cycle processes induced by climate warming over the three rivers source region

The relationship between the ocean, land, and atmosphere is greatly impacted by climate change, and the atmospheric water cycle constitutes the most active and crucial hub in this interaction. Two crucial components of the atmospheric water cycle are the precipitation recycle ratio (PRR) and the water vapor source. Accurate quantification of these components can greatly assist in a better understanding of the atmospheric water cycle processes and variations. In this study, measured data from radiosondes and meteorological stations are used to assess the accuracy of the ERA5 reanalysis dataset. The Mann-Kendall (M-K), empirical orthogonal function (EOF), and probability density function (PDF) are utilized to analyze the spatiotemporal variations in the components of the atmospheric water cycle and to trace the sources of water vapor. Based on the Brubaker model, the PRR is estimated, and the atmospheric water cycle process over the three rivers source region (TRSR) is quantified. The findings reveal that (1) there is a significant increase in temperature, precipitation, evaporation, and water vapor content over the TRSR from 1979 to 2020, and the distribution of precipitation and water vapor content decreases from southeast to northwest. (2) The South Asian monsoon and westerly winds are the predominant atmospheric cycle systems for water vapor transport over the TRSR. The water vapor input at the western, southern, and northern borders all exhibit an increasing trend (0.16 × 105 kg s−1 a−1, 0.18 × 105 kg s−1 a−1, 0.09 × 105 kg s−1 a−1, respectively, p > 0.05), while the water vapor output at the eastern border exhibits a decreasing trend (−0.009 × 105 kg s−1 a−1, p > 0.05), resulting in a significant increase in net water vapor influxes (0.43 × 105 kg s−1 a−1, p < 0.05). Water vapor convergence occurs in the southeast while water vapor dispersion occurs in the northwest regions of the TRSR. (3) The multi-year average PRR is 20.85%, with a slightly declining trend, and the contribution of external moisture transport to regional precipitation is dominant over the TRSR. Climate change has sped up the atmospheric water cycle over the TRSR between 1979 and 2020: for every 1 °C rise in temperature, water vapor content increased by 6.83%, precipitation increased by 4.71%, and evaporation increased by 3.62%.

How does Mei-yu precipitation respond to climate change?

Mei-yu is an important weather phenomenon in the middle-lower Yangtze River valley (YRV) region. This study investigates the changes in the characteristics of Mei-yu under global warming and the potential reasons based on observation and reanalysis data during 1961-2022. Notable increasing long-term trends are detected in the number of days without rainfall (NDWOR), the intensity of rainfall events, and the frequency and intensity of extreme precipitation events (EPEs) in the YRV region during the Mei-yu period (15 June-10 July) over past decades. The increasing trend in NDWOR is attributed to decreased relative humidity over land surface and a longer time for the air to be replenished with moisture after rainfall events in a warming climate. The increasing trends in the intensity of rainfall events and frequency/intensity of EPEs are attributed to the strengthened transient water vapor convergence and convection in the atmosphere under global warming. Furthermore, the response of Mei-yu to 2°C of global warming with respect to the pre-industrial climate is analysed using CMIP6 models. The results suggest that the NDWOR, intensity of rainfall events and frequency of EPEs will increase in the YRV region during the Mei-yu period under the 2°C warming scenario, which implies a more challenging climate risk management in the future. Overall, the intensity of rainfall events during the Mei-yu period has the most significant response to climate change in observations and projections. The model results have a relatively large uncertainty.

Variations in Key Factors at Different Explosive Development Stages of an Extreme Explosive Cyclone over the Japan Sea

Explosive cyclones (ECs) occur frequently over the Japan Sea. The most rapidly intensifying EC over the Japan Sea during the 44-year period 1979–2022, in the cold season (October–April), was examined to reveal the variations in the key factors at different explosive development stages. The EC deepened at a maximum deepening rate of 3.07 bergerons and explosive development lasted for 15 h. At the initial moment of explosive development, the EC had distinctive low-level baroclinicity, the low-level water vapor convergence was weak, and mid-level cyclonic vorticity advection was far away from the EC’s center. At the moment at which the EC reached the maximum deepening rate, the low-level water vapor convergence and mid-level cyclonic vorticity advection increased distinctly and approached the EC’s center. A diagnostic analysis using the Zwack–Okossi equation showed that the main contributor to the initial explosive development was warm-air advection. Through the evolutionary process of the explosive development, the non-key factors of the cyclonic vorticity advection and diabatic heating at the initial explosive development stage increased quickly and became key factors contributing to the maximum explosive development. The key factors contributing to the explosive development varied with the stage of explosive development. The cross-section and vertical profile of each term suggested that the cyclonic vorticity advection was enhanced in the upper troposphere and diabatic heating increased in the middle troposphere.

Mechanical and Thermal Forcings of Asian Large-Scale Orography on Spring Cloud Amount and Atmospheric Radiation Budget over East Asia

Abstract Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerable spring top-of-the-atmosphere (TOA) radiative cooling over Southeast China (SEC) is very likely related to upstream orography forcing. Here we investigate the mechanical and thermal forcings of Asian large-scale orography, particularly the Tibetan Plateau (TP), on downstream East Asian cloud amount and atmospheric radiation budget during March–April using the Global Monsoons Model Intercomparison Project simulations. The thermal forcing drives significant surface heating and a low-level cyclone over the TP, pumping low-level air to the middle troposphere. Ascent and water vapor convergence triggered by the thermal forcing favor air condensation, low–middle clouds, and resultant strong spring cloud radiative cooling over SEC. Moreover, the thermal forcing moves the position of cloud radiative cooling westward toward the TP. The TP’s blocking role weakens low-level westerlies over SEC, but its deflecting role increases downstream high-level westerlies, dynamically favoring cloud formation over SEC and the eastward ocean. In addition, the TP can force ascent and increase cloud amounts over the western and central TP. The thermal forcing contributes to 57.1% of total cloud amount and 47.6% of TOA cloud radiative cooling induced by the combined orography forcing over SEC while the mechanical one accounts for 79.4% and 95.8% of the counterparts over the ocean to the east of SEC. Our results indicate that Asian large-scale orography shapes the contemporary geographical distribution of spring East Asian cloud amount and atmospheric radiation budget to a large extent. Significance Statement Clouds tied to large-scale topography and circulation exhibit some remarkable geographical distributions. The global strongest cloud radiative cooling, with an intensity of up to −90 W m−2, occurs over Southeast China (SEC) during March–April. The primary purpose of this study is to understand the influences of Asian large-scale orography, particularly the Tibetan Plateau (TP), on this unique climatic phenomenon using the latest climate model simulations. Our results show that Asian large-scale orography forcing significantly increases ascent, low–middle cloud formation, and resultant strong spring cloud radiative cooling over SEC and downstream ocean. The sensible-heat-driven air pump induced by the TP’s thermal forcing maintains strong cloud radiative cooling over SEC. This study provides valuable insights that link Asian large-scale orography forcing to downstream cloud–radiation characteristics.

Anthropogenic impact on the severity of compound extreme high temperature and drought/rain events in China

Compared with individual extreme events, compound events have more severe impacts on humans and the natural environment. This study explores the change in severity of compound extreme high temperature and drought/rain events (CHTDE/CHTRE) and associated influencing factors. The CHTDE and CHTRE intensified in most areas of China in summer (June–July August) during 1961–2014. Under global warming, the increased water-holding capacity of the atmosphere and the decreased relative humidity led to an increase in the severity of CHTDE. The severity of CHTRE is increased because of enhanced transient water vapor convergence and convective motion. Anthropogenic climate change, especially greenhouse gas forcing, which contributes 90% to the linear change in the severity of CHTDE and CHTRE, is identified as the dominant factor affecting the severity of CHTDE in China. In addition, the historical natural forcing (hist-NAT) may be related to the interannual-to-decadal variability in the severity of CHTDE/CHTRE.

Interdecadal variability of summer extreme rainfall in the Huai River basin of China associated with the Asian‐Pacific Oscillation

AbstractUsing the rainfall data at rain gauge stations in China and the European Center for Medium‐Range Weather Forecast (ECMWF) reanalysis, the daily Asian‐Pacific Oscillation (APO) index, a tropospheric temperature thermal contrast between Asia and the North Pacific, is constructed to investigate an interdecadal relationship between summer (June–July) APO and rainfall in the Huai River basin (HRB) of central‐eastern China. The daily APO index averaged over June 22–July 12 shows an interdecadal shift around the late 1990s. This shift is characterized by a negative phase of the daily APO index during 1987–1996 and a subsequent positive phase during 1997–2006. Accompanying this shift, the occurrence frequency, intensity and amount of extreme rainfall events remarkably increase in the HRB region. The increased rainfall can be reasonably explained by the atmospheric circulation anomalies. Corresponding to the decadal change in the summer daily APO from the negative phase to the positive one, the subtropical high pressure over the western North Pacific moves toward the north and easterly wind anomalies in the middle and lower layers of the troposphere prevail over extratropical East Asia, which strengthens water vapour convergence, the instability of atmospheric stratification and upward motion anomalies in the HRB region.