Search Results (32)

By utilizing daily precipitation data from 400 meteorological stations in the Yellow River Basin (YRB) of China, atmospheric and oceanic reanalysis data, this study investigates the climatological characteristics, leading modes, and relationships with atmospheric circulation and sea surface temperature (SST) of summer extreme precipitation in the YRB from 1981 to 2020 through the extreme precipitation metrics and Empirical Orthogonal Function (EOF) analysis. The results indicate that both the frequency and intensity of extreme precipitation exhibit an eastward and southward increasing pattern in terms of climate state, with regions of higher precipitation showing greater interannual variability. When precipitation in the YRB exhibits a spatially coherent enhancement pattern, high latitudes exhibits an Eurasian teleconnection wave train that facilitates the southward movement of cold air. Concurrently, the northward extension of the Western Pacific subtropical high (WPSH) enhances moisture transport from low latitudes to the YRB, against the backdrop of a transitioning SST pattern from El Niño to La Niña. When precipitation in the YRB shows a “south-increase, north-decrease” dipole pattern, the southward-shifted Ural high and westward-extended WPSH converge cold air and moist in the southern YRB region, with no dominant SST drivers identified. Full article

Weather patterns substantially influence extreme weathers in Japan. Extreme high temperature events can cause serious health problems, including heat stroke. Therefore, understanding weather patterns, along with their impacts on human health, is critically important for developing effective public health measures. This study examines the impact of weather patterns on heat stroke risk, focusing on a two-tiered high-pressure system (DH: double high) consisting of a lower tropospheric western Pacific subtropical high (WPSH) and an overlapping upper tropospheric South Asian high (SAH), which is thought to cause high-temperature events in Japan. In this study, the self-organizing map technique was utilized to investigate the relationship between pressure patterns and the number of heat stroke patients in four populous cities. The study period covers July and August from 2008 to 2021. The results show that the average number of heat stroke patients in these cities is higher on DH days than on WPSH days in which SAH is absent. The probability of an extremely high daily number of heat stroke patients is more than twice as high on DH days compared to WPSH days. Notably, this result remains true even when WPSH and DH days are compared within the same air temperature range. This is attributable to the higher humidity and stronger solar radiation under DH conditions, which enhances the risk of heat stroke. Large-scale circulation anomalies similar to the Pacific–Japan teleconnection are found on DH days, suggesting that both high humidity and cloudless conditions are among the large-scale features controlled by this teleconnection. Early countermeasures to mitigate heat stroke risk, including advisories for outdoor activities, should be taken when DH-like weather patterns are predicted. Full article

The seasonal and interannual variations in ground-level ozone across eastern China from 2014 to 2022 were strongly influenced by meteorological conditions and large-scale atmospheric circulations. We applied empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses to explore these relationships. The EOF analysis identified three primary patterns of ozone variability: a dominant seasonal cycle over most of mainland China, an anti-correlation between northern and southern China during transitional seasons, and elevated springtime ozone concentrations in coastal regions. The SVD results further demonstrated that seasonal ozone variability was primarily driven by the annual radiation cycle across much of China. In contrast, the East Asian summer monsoon (EASM) was linked to the relatively low summer ozone levels observed in southern China. The anti-correlation between northern and southern China was associated with western Pacific subtropical high (WPSH) movement, which promoted sunny weather conditions and was conducive to ozone formation. Additionally, high springtime ozone levels in northern coastal regions were influenced by pollutant transport from continental cold high (CCH) events, while the cloud-free conditions and intense solar radiation in southern China contributed to elevated ozone concentrations. Full article

This study analyzed the change in and mechanisms of summer extreme precipitation in Southwest China (SWC) during 1979–2021. The trend in summer extreme precipitation showed an evident interdecadal mutation in the late 1990s; it decreased during 1979–1996 (P1) and increased during 1997–2021 (P2). It is observed that the moisture flux in SWC is more abundant in P2 than in P1. The South Asian high (SAH) and western Pacific subtropical high (WPSH) contributed to the change in extreme precipitation in SWC. Both the SAH and WPSH weakened in 1979–1996 and enhanced in 1997–2021. The enhanced SAH and WPSH are conducive to forming updrafts in SWC and transporting moisture from the Bay of Bengal (BOB) and South China Sea (SCS) into SWC. Further research found that the causes for the interdecadal variation of the SAH and WPSH are the anomalies of sensible heat flux (SSH) over the Tibetan Plateau (TP) and sea surface temperature (SST) in the tropical western Pacific–Indian Oceans. The SSH is the main energy source of troposphere air and an essential component of the surface heat balance because it can maintain the intensity and influence range of the SAH. The increasing SST stimulated strong upward motion and thus maintained the strength of the WPSH, which also made the WPSH extend westward into mainland China. This study also summarized local human adaptation to climate change. The use of advanced science and technology to improve monitoring and forecasting ability is an important measure for human society to adapt to climate change. At the same time, increasing the participation of individuals and social organizations is also an indispensable way to increase human resilience to climate change. Full article

A rare compound hot and drought (CHD) event occurred in the Yangtze River Basin (YRB) in the summer of 2022, which brought serious social crisis and ecological disaster. The analysis of the causes, spatiotemporal characteristics and impacts of this event is of great significance and value for future drought warning and mitigation. We used the Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) data, meteorological data, hydrological data and satellite remote sensing data to discuss the spatiotemporal evolution, formation mechanism and the influence of the CHD event. The results show that the drought severity caused by the CHD event was the most severe during 2003 and 2022. The CHD event lasted a total of five months (from July to November), and there were variations in the damage in different sub-basins. The Wu River Basin (WRB) is the region where the CHD event lasted the longest, at six months (from July to December), while it also lasted four or five months in all the other basins. Among them, the WRB, Dongting Lake Rivers Basin (DLRB) and Mainstream of the YRB (MSY) are the three most affected basins, whose hot and drought severity values are 7.750 and −8.520 (WRB), 7.105 and −9.915 (DLRB) and 6.232 and −9.143 (MSY), respectively. High temperature and low precipitation are the direct causes of the CHD event, and the underlying causes behind this event are the triple La Niña and negative Indian Ocean Dipole event. The two extreme climate events made the Western Pacific Subtropical High (WPSH) unusually strong, and then the WPSH covered a more northerly and westerly region than in previous years and remained entrenched for a long period of time over the YRB and its adjacent regions. Moreover, this CHD event had a devastating impact on local agricultural production and seriously disrupted daily life and production. Our results have implications for the study of extreme disaster events. Full article

The impacts of Arctic sea ice on climate in middle and high latitudes have been extensively studied. However, its effects on climate in low latitudes, particularly on summer monsoon rainfall in the South China Sea (SCS), have received limited attention. Thus, this study investigates the connection between the Arctic sea ice concentration (SIC) anomaly and the early summer monsoon rainfall (ESMR) in the SCS and its underlying physical mechanism. The results reveal a significant positive correlation between the Barents Sea (BS) SIC in May and the ESMR in the SCS. When there is more (less) SIC in the Barents Sea (BS) during May, this results in a positive (negative) anomaly of the local turbulent heat flux, which lasts until June. This, in turn, excites an upward (downward) air motion anomaly in the vicinity of the BS, causing a corresponding downward (upward) motion anomaly over the Black Sea. Consequently, this triggers a wave train similar to the Eurasian (SEU) teleconnection, propagating eastward towards East Asia. The SEU further leads to an (a) upward (downward) motion anomaly and weakens (strengthens) the western Pacific subtropical high (WPSH) over the SCS, which is accompanied by a southwest adequate (scarce) water vapor anomaly transporting from the Indian Ocean, resulting in more (less) precipitation in the SCS. Furthermore, the response of ESMR in the SCS to the SIC in the BS is further verified by using the Community Atmosphere Model version 5.3 (CAM5.3). This study introduces novel precursor factors that influence the South China Sea summer monsoon (SCSSM), presenting a new insight for climate prediction in this region, which holds significant implications. Full article

The westerly circulation and the monsoon circulation are the two major atmospheric circulation systems affecting the middle latitudes of the Northern Hemisphere (NH), which have significant impacts on climate and environmental changes in the middle latitudes. However, until now, people’s understanding of the long-term paleoenvironmental changes in the westerly- and monsoon-controlled areas in China’s middle latitudes is not uniform, and the phase relationship between the two at different time scales is also controversial, especially the exception to the “dry gets drier, wet gets wetter” paradigm in global warming between the two. Based on the existing literature data published, integrated paleoenvironmental records, and comprehensive simulation results in recent years, this study systematically reviews the climate and environmental changes in the two major circulation regions in the mid-latitudes of China since the Middle Pleistocene, with a focus on exploring the phase relationship between the two systems at different time scales and its influencing mechanism. Through the reanalysis and comparative analysis of the existing data, we conclude that the interaction and relationship between the two circulation systems are relatively strong and close during the warm periods, but relatively weak during the cold periods. From the perspective of orbital, suborbital, and millennium time scales, the phase relationship between the westerly and Asian summer monsoon (ASM) circulations shows roughly in-phase, out-of-phase, and anti-phase transitions, respectively. There are significant differences between the impacts of the westerly and ASM circulations on the middle-latitude regions of northwest China, the Qinghai–Tibet Plateau, and eastern China. However, under the combined influence of varied environmental factors such as BHLSR (boreal high-latitude solar radiation), SST (sea surface temperature), AMOC (north Atlantic meridional overturning circulation), NHI (Northern Hemisphere ice volume), NAO (North Atlantic Oscillation), ITCZ (intertropical convergence zone), WPSH (western Pacific subtropical high), TIOA (tropical Indian Ocean anomaly), ENSO (El Niño/Southern Oscillation), CGT/SRP (global teleconnection/Silk Road pattern), etc., there is a complex and close coupling relationship between the two, and it is necessary to comprehensively consider their “multi-factor’s joint-action” mechanism and impact, while, in general, the dynamic mechanisms driving the changes of the westerly and ASM circulations are not the same at different time scales, such as orbital, suborbital, centennial to millennium, and decadal to interannual, which also leads to the formation of different types of phase relationships between the two at different time scales. Future studies need to focus on the impact of this “multi-factor linkage mechanism” and “multi-phase relationship” in distinguishing the interaction between the westerly and ASM circulation systems in terms of orbital, suborbital, millennium, and sub-millennium time scales. Full article

The Yangtze River Delta (YRD) is an important economic region in China. Heavy winter rainfall may pose serious threats to city operations. To ensure the safe operation of the city, meteorological departments need to provide forecast results for the Spring Festival travel rush weather service. Therefore, the extended-range forecast of winter rainfall is of considerable importance. To solve this problem, based on the analysis of low-frequency rainfall and the intra-seasonal oscillation of atmospheric circulation, an extended-range forecast model for winter rainfall is developed using spatiotemporal projection methods and is applied to a case study from 2020. The results show that: (1) The precipitation in the YRD during the winter has a significant intra-seasonal oscillation (ISO) with a periodicity of 10–30 d. (2) The atmospheric circulations associated with winter rainfall in the YRD have a significant characteristic of low-frequency oscillation. From a 30-day to a 0-day lead, large modifications appear in the low-frequency atmospheric circulations at low, mid, and high latitudes. At low latitudes, strong wet convective activity characterized by a negative OLR combined with a positive RH700 correlation coefficient moves northwestward and covers the entire YRD. Meanwhile, the Western Pacific subtropical high (WPSH) characterized by a positive Z500 anomaly enhances and lifts northward. At mid and high latitudes, the signal of negatively correlated Z500 northwest of Lake Balkhash propagates southeastward, indicating the cold is air moving southward. Multiple circulation factors combine together and lead to the precipitation process in the YRD. (3) Taking the intra-seasonal dynamical evolution process of the atmospheric circulation as the prediction factor, the spatiotemporal method is used to build the model for winter mean extended-range precipitation anomaly tendency in the YRD. The hindcast for the recent 10 years shows that the ensemble model has a higher skill that can reach up to 20 days. In particular, the skill of the eastern part of the YRD can reach 25 days. (4) The rainfall in the 2019/2020 winter has a significant ISO. The ensemble model could forecast the most extreme precipitation for 20 days ahead. Full article

The study aimed to investigate the spatiotemporal variation of annual precipitation and extreme precipitation within the Songhua River Basin (SRB). It utilized precipitation data collected from 60 meteorological stations within the SRB during the period 1968–2019. Employing Empirical Orthogonal Function (EOF) analysis, it decomposed spatiotemporal characteristics of annual precipitation in the SRB. Through Pearson correlation analysis, application of the cross-wavelet transform, and wavelet coherence analysis, the current study explored the correlation between geographical factors, local air temperature, circulation factors, and annual and extreme precipitation. The results indicated an increasing trend for annual precipitation and for most indices of extreme precipitation within the SRB, apart from the consecutive dry days (CDD). Spatially, a general pattern of “more in the east and less in the west” was observed. Annual precipitation types in the basin were resolved into two modes with the first mode showing a general tendency of more (or less) precipitation over the entire basin, while the second mode exhibited less (or more) precipitation in the western areas and more (or less) in the eastern areas. Longitude, latitude, and altitude significantly impacted annual precipitation and extreme precipitation. Local air temperature notably affected the consecutive wet days (CWD). The West Pacific Subtropical High (WPSH) exerts a strong influence on the annual precipitation and extreme precipitation within the basin. Full article

Marine heatwaves (MHWs) are becoming more frequent and intense in many regions around the world, as well as in China’s marginal seas. However, the seasonal characteristics and associated physical drivers of MHWs are largely unknown. In this study, we analyze, based on multiple reanalysis and numerical model data, the seasonal characteristics and causes of MHWs in the South China Sea (SCS) over a near 30-year period (1991–2022). There exist significant seasonal variabilities in the spatiotemporal features and formation mechanisms of MHWs. MHWs in the SCS show significant increasing trends in terms of frequency, duration, and intensity. MHWs during the summer half-year are stronger than the winter half-year as a whole, with them being more likely to occur over the eastern SCS in the summer half-year and the western region in the winter half-year. However, the increasing trend of MHWs in the winter half-year exceed those in the summer. Additionally, we find that MHWs are associated with the unusually strong west Pacific subtropical high (WPSH) both in the summer and winter half-years. Nevertheless, the dominant factors for MHWs are different in the varied seasons. According to upper ocean temperature equation analysis, surface heat flux anomalies (especially shortwave radiation flux) are major effect factors in the summer half-year, while ocean dynamic processes play the main role in the winter half-year. An analysis of the typical MHWs also proves this conclusion. Moreover, MHWs occurring in winter are often accompanied by temperature anomalies within the mixed-layer depth. The findings imply that the formation mechanisms and space–time distribution of MHWs exist with a seasonal contrast in the SCS, rather than simply being due to large-scale circulation and flux anomalies. This may provide a useful reference for a deeper understanding and forecasting of MHWs under different seasons and weather. Full article

It is necessary to alleviate the high temperatures and heat wave disasters in cities in southwest China that are beginning to occur because of global warming. During this study, the spatial and temporal characteristics of heat waves in Nanchong from 1961 to 2022 are analyzed by using the signal smooth method and mutation test. Based on the meteorological data and socioeconomic statistics, the entropy value method is used to obtain the indicator weights to construct a heat wave social vulnerability evaluation index system and conduct vulnerability assessments and classifications. The results show that: ① The heat wave indicators in Nanchong show an increasing trend, although there is a low period of heat waves from 1980 to 1995. Additionally, there are significant mutations in the number of days, frequency, and intensity of high-temperature heat waves from 2009 to 2011, which may be caused by the abnormal high-pressure belt in the mid-latitude. ② The distribution of exposure, sensitivity, and adaptability in Nanchong City, under high temperatures, is uneven in space. Generally, the indicators in the north are lower than those in the south. ③ The high-vulnerability counties are mainly distributed in the east and west of Nanchong, the proportion of the medium social vulnerability index areas are more than a half, while the dominant factor in the distribution pattern is natural factors. ④ The Western Pacific Subtropical High (WPSH) anomaly directly led to the extremely high temperature in Nanchong in the summer of 2022, and the urbanization process index shows a significant positive correlation with the trend of high temperatures and heat waves in Nanchong. Full article

Under the background of global warming, climate extremes have become a crucial issue with distinct heterogeneity features in different regions. Hence, spatial–temporal changes in temperature and precipitation extremes in Guizhou Province were investigated utilizing daily maximums and minimums of temperature and daily precipitation data during 1960–2019 based on trend analysis. It was concluded that, firstly, all warm extremes but warm spell duration indicator (WSDI) are significantly enhanced, whereas for cold extremes, the monthly minimum value of daily minimum temperature (TNn) is significantly enhanced, while cool nights (TN10P), frost days (FD0), ice days (ID0), and cold spell duration indicator (CSDI) are significantly decreased. And all precipitation extremes but consecutive wet days (CWD) have no significant variational trend in Guizhou Province. Secondly, variational trends of temperature extremes are more prominent and robust in western Guizhou Province. Temperature and precipitation extremes show large differences from spring to winter. Thirdly, temperature extremes are closely correlated with strength, area, and the westernmost ridge point index of western Pacific subtropical high (WPSH), whereas precipitation extremes show no distinct correlation with WPSH. The WPSH has significantly strengthened and shifted westward in the past 60 years, leading to less total cloud cover and more downward solar wave flux reaching Earth’s surface, accordingly, exacerbating warm extremes and weakening cold extremes. These results will benefit understanding the heterogeneity of climate extremes at a regional scale. Full article

Extreme precipitation events frequently occur at the southeastern edge of the Tibetan Plateau (SETP), causing severe disasters. In this study, we selected the top 100 regional extreme precipitation events over the SETP region during the period of 2001–2020, and analyzed their evolutionary characteristics of large-scale thermodynamic anomalies prior to the extreme precipitation events occurring, with the aim of exploring their precursor signals. The results show that, accompanying the wave train propagating across the Eurasian continent and reaching East Asia, the extreme events over SETP during the summer season are dominated by the background large-scale atmospheric circulations characterized by the strengthened Southern Asia high (SAH), the westward-extended Western Pacific subtropical high (WPSH), and an intensified eastern Asia trough. Additionally, an analogue of low-level vortex embedded in the background large-scale circulations is developed at least 4 days prior to the occurrence of extreme events. Under the combined effects of these anomalies, the warm and cold air converge in the SETP area. Further analysis also suggests that the upper-troposphere divergence aloft combined with lower pressures at surface level lead to the upward vertical motion of circulations, along with the enhanced water-vapor transport conveyed both by the East Asian summer monsoon and the Indian summer monsoon. All anomalies mentioned above provide the favorable environment for the occurrence of precipitation extremes in the SETP region. Full article

Many previous studies have shown that atmospheric circulation anomalies are usually the direct cause of extreme high temperatures (EHT). However, the atmospheric circulation anomalies associated with daytime and nighttime EHTs in North China and their differences are less discussed. The present study divides the summer EHTs in North China into independent daytime EHT (ID-EHT) and independent nighttime EHT (IN-EHT) according to the 90th percentile thresholds of the daily maximum and minimum temperature from CN05.1 and compares their atmospheric circulation anomalies. Composite results show that the sinking motion anomaly over North China and the southward displacement of the Western Pacific Subtropical High (WPSH) cause less low cloud cover and water vapor, which is conducive to absorbing more solar radiation at the surface, and leads to the daytime high temperature of ID-EHT. With the disappearance of solar radiation at night, the heat is rapidly dissipated, and the high temperature cannot be maintained. A wave train from high latitudes can affect ID-EHT weather. On the contrary, the upward motion anomaly over North China cooperates with the northward displacement of the WPSH, leading to more clouds and water vapor over North China. As a result, the absorption of solar radiation in North China during the daytime is reduced, and EHT has difficulty in forming during the day. The higher humidity causes slower heat loss from daytime to nighttime, resulting in an IN-EHT. IN-EHT is more likely to be affected by a wave train such as the Silk Road pattern from the midlatitudes. Full article

In order to find potential low-frequency signals and provide new ideas for extended-range forecasting, the intraseasonal oscillation (ISO) characteristics of persistent high temperature events (PHTEs) in the extended summer in Jiangnan area are explored by using daily maximum air temperature (Tmax) data from the China Meteorological Data Network and daily reanalysis data provided by NCEP/DOE. The results show that the low-frequency PHTEs can be classified into three types according to the position variation of the Western Pacific subtropical high (WPSH). For the first two types of PHTEs, a southwestward migrating mid-latitude wave train from the North American coast to the central and eastern China can be clearly seen in the whole troposphere. Whereas the two types of PHTEs show different features in the low-latitude. It is found that a significantly westward extension of the WPSH during the first type of PHTEs, with the low-frequency anticyclone moving westward in the mid-lower troposphere. For the second type of PHTEs, the WPSH is mainly located in the southeastern China with slightly movement. Analysis of the low-frequency vertical circulation and the thermodynamic equation further reveal that the increase of temperature in Jiangnan region is primarily attributed to the descending airflow. Full article