In China, the middle and lower reaches of the Yangtze River basin (MLRYRB) is a core region suffering frequent devastating floods triggered by heavy precipitation during warm seasons, exerting serious impacts on society. However, the physical mechanisms responsible for the increasing flood-inducing rainfall (FIR) frequency over MLRYRB during warm seasons remain unclear. Based on objective definition procedures, the present study investigates the salient atmospheric and oceanic signals tied to the interannual fluctuations of warm-season FIR frequency over MLRYRB. The results show that the suppressed convection from the remote western Pacific to the east of the Philippines could serve as a salient synchronous atmospheric signal for the increased FIR frequency. Moreover, the sea surface temperature (SST) warming over the tropical Indian Ocean (TIO) and the preceding wintertime El Niño-related SST anomaly pattern are deemed as salient contemporaneous and precursory oceanic signals linking the enhancement of the warm-season FIR frequency over MLRYRB on the interannual timescale, respectively. Further observational evidence and tropical Pacific pacemaker experiment results based on the Community Earth System Model Version 2 (CESM2) suggest that the mature El Niño in the prior winter can exert a delayed impact on the enhanced FIR frequency over MLRYRB during the subsequent warm season by exerting vital contributions to the FIR-favorable systems (i.e., southwestward-shifted western North Pacific anomalous anticyclone and the southward-displaced East Asian subtropical westerly jet). The basin-wide positive TIO SST anomalies act as El Niño’s capacitor to relay its impact. These signals have important implications for seasonal prediction of FIR frequency over MLRYRB, and it is essential to place a high requirement on consideration of the better-known El Niño’s cross-season atmospheric teleconnection.

This study investigates the physical mechanisms for the persistent heavy rainfall (PHR) events over South China (SC) associated with the 10–30-day intraseasonal oscillation (ISO) before the South China Sea Summer Monsoon (SCSSM) onset (SCSSM-I) and after the SCSSM onset (SCSSM-II) in the first rainy season (April–June). About 25.0

The northwestern Pacific monsoon trough (NWPMT) deeply impacts socio-economic development and human security over East Asia by supplying moisture to the summer monsoon rainfall and modulating tropical cyclone activities. However, considerable inter-model spreads in the coupled model inter-comparison project phase 6 models make the future projection of the NWPMT less reliable. Here, we find that the inter-model spread of the NWPMT change is significantly correlated with the central equatorial Pacific sea surface temperature change, and mainly determined by the equatorial thermocline sharpness in the historical simulations. According to the emergent constraint method, the central equatorial Pacific SST would warm up about 6% slower than the multi-model mean with 56% uncertainty reduced. Correspondingly, the NWPMT would slacken westward with 36% uncertainty reduced. Results here emphasize the importance of examining and reducing systematic model biases in simulating thermocline sharpness that have been overlooked in past literatures, before achieving more reliable future projections.

Haze days in Guangdong Province (GD) occur mainly in winter, with the highest number of moderate/severe haze days occurring in January. The interannual variability of winter haze days in GD is closely related to the Siberian High, the Aleutian Low, the East Asian Trough, the 850-hPa meridional wind over eastern China, and the 200-hPa East Asian Jet. We construct a winter comprehensive circulation index (WCIDX) to express the joint effects of the above regional-scale circulations on haze days in GD. The positive phase of WCIDX is closely linked to the Eurasian teleconnection pattern, which induces the abnormal southerly winds, high temperatures, and enhanced precipitation over GD by modulating the regional atmospheric circulations, localized meteorological conditions (i.e., enhanced lower specific humidity, reduced planetary boundary layer height, decreased surface wind speed, and enhanced low-level atmospheric inversion) conductive to a higher haze in GD. In addition, the positive phase of the WCIDX favors enhancement of the positive 850-hPa Eady growth rate (EGR) over the mid–high-latitude areas of East Asia, which enhances atmospheric baroclinity and results in a northward shift of the East Asian Jet. Pollutants accumulated over the Indochina Peninsula are advected to GD by the southwesterly airflows. It was found that enhanced horizontal warm advection, adiabatic heating, and diabatic heating provide conditions favorable for low-level atmospheric inversion.

The springtime haze events in Guangdong Province are mainly located in the Pearl River Delta (PRD) region, which has the second highest number of haze days among four seasons. The major regional-scale circulation patterns affecting the interannual spring haze days in the PRD region are closely associated with high pressure extending from Baikal Lake to Okhotsk Sea, the North Pacific low pressure, the East Asian Trough, low-level meridional wind over eastern China, and upper tropospheric East Asian Jet. We define a comprehensive circulation index (CCIDX) to express joint effects of major regional-scale circulations. The positive phase of the CCIDX is intimately linked to negative Scandinavian Peninsula (SCAND)-like and WP teleconnection patterns, which induces abnormal northerly winds, low temperatures, and less precipitation over the PRD region by modulating regional atmospheric circulations. In addition, the positive CCIDX favors the enhancement the negative 850 hPa Eady growth rate over the middle and high latitude areas in East Asia, thus weakening the atmosphere baroclinity in the lower troposphere and hampering transportation of pollutants north of southern China into the Pacific Ocean. As such, pollutants accumulated to the north of southern China are advected to the PRD region by pronounced low-level northerly airflows. The positive phase of the CCIDX can provide favorable local meteorological circumstances (i.e., enhanced vertical descending motion, reduced lower specific humidity, decreased surface wind speed, and enhanced low-level atmospheric inversion) required for the increased incidence of haze pollution over the PRD region. It is found that the increase of specific humidity with height, which is mainly contributed by horizontal moisture advection and apparent moisture sink, contributes largely to the sustainability of low-level atmospheric inversion in the PRD region via absorptions of long-wave radiation. Above 700 hPa, enhanced horizontal warm advection and diabatic heating also provide favorable conditions for maintenance of low-level atmospheric inversion.

An observed fact is proposed that the 2020 record-breaking Meiyu over the Yangtze–Huaihe River Basin (YHRB) is characteristic of significant subseasonal variation. The anomalously enhanced rainfall experiences a southward retreat from the northern YHRB in June to the southern YHRB in July. The meridional shift of abnormal rainbelt is closely related to the different anomalous Meiyu front circulations. The first stage features a warm Meiyu front with an extremely strong northward transport of warm-and-wet air, whereas a cold front forms with a convergence between the strong northeasterlies and southwesterlies in July. Another significant subseasonal variation of the 2020 Meiyu is that the Meiyu rainfall evolves in a periodic quasi-biweekly oscillation (QBWO). On the scale of the QBWO, the cold air activities over East Asia contribute significantly to Meiyu; each intense southward invasion of cold air corresponds well to the enhancement of Meiyu rainfall. However, the location of the western Pacific subtropical high, the subtropical East Asia summer monsoon (SEASM), and the intensity of the East Asia subtropical westerly jet exhibit opposite QBWO characteristics in June and July. For an increasing (decreasing) of Meiyu rainfall, the western Pacific subtropical high marches northward (retreats southward), the subtropical East Asia summer monsoon weakens (strengthens), and the East Asia subtropical westerly jet accelerates (decelerates) in June. The opposite holds true in July. Further analyses reveal that the filtered cyclone over Northeast China benefiting the southward intrusion of cold air is associated with the eastward propagation of a wave train over the mid-high latitudes in June, whereas it arises from both the westward propagation of a wave train over the mid-high latitudes and the northward propagation of cyclonic circulation from the tropics in July.

East Asia is undergoing significant climate changes and these changes are likely to grow in the future. It is urgent to characterize both the mechanisms controlling climate and the response of the East Asian climate system at global warming of 1.5 and 2 °C above pre-industrial levels (GW1.5 and GW2 hereafter). This study reviews recent studies on East Asian climate change at GW1.5 and GW2. The intensity and variability of the East Asian summer monsoon are expected to increase modestly, accompanied by an enhancement of water vapor transport. Other expected changes include the intensification of the Western Pacific Subtropical High and an intensified and southward shift of the East Asian jet, while the intensity of the East Asian winter monsoon is projected to reduce with high uncertainty. Meanwhile, the frequency of ENSO may increase in a warming world with great uncertainty. Significant warming and wetting occur in East Asia, with more pronounced intensity, frequency, and duration of climate extremes at GW2 than that at GW1.5. The fine structure of regional climate changes and the presence and location of various warming hotspots, however, show substantial divergence among different model simulations. Furthermore, the Asian climate responses can differ substantially between the transient and stabilized GW1.5 and GW2, which has important implications for emission policies. Thus, to better plan effective mitigation and adaptation activities, further research including an in-depth exploration of the divergent responses in transient versus stabilized scenarios, the quantification of future projection uncertainties, and improvements of the methods to reduce model uncertainties are required.

采用目前国家干旱监测业务实行的MCI指数,利用Morlet小波、经验正交函数(EOF)等方法,分析了福建省1961—2019年全省66个气象站MCI指数表征的干湿状况和干旱变化特征.结果表明:福建省存在明显的干湿气候特征,具有显著的6—8 a和22 a的周期振荡,内陆山区干湿变化周期比沿海长,在季节尺度上各季均存在多时间尺度和地域差异化的特点;其空间变化具有3种典型模态,反映了季风降水多寡和地形差异.MCI表征的干旱过程时空分布与历史干旱事件相吻合,秋季和冬季是福建省干旱发生频率最高的季节,春季和夏季是干旱强度最强的季节;闽江口以南沿海地区干旱发生率明显高于内陆地区,全省出现同步干旱的机率较小(12％).

本文通过总结2000—2018年中国知网核心数据库的232篇关于冬季风的古气候文献,结合计量学分析,得到冬季风的历史演变及其中存在的问题:大部分的研究认为,亚洲冬季风形成时间基本在8.2～7.4 MaBP,青藏高原的隆升以及我国北方大面积出现的代表冬季风的风尘堆积可能是冬季风形成的重要标志.自冬季风形成至130 kaBP时期冬季风以加强为主,73 kaBP以后得到的冬季风强度演变结论差距较大,甚至相反.总结冬季风的驱动机制研究来看,新生代至第四纪的冬季风以青藏高原的隆升作用影响为主;第四纪至全新世(甚至早至上新世晚期以来)东亚冬季风主要受到冰盖、全球冰量、太阳辐射量等的影响;而全新世以来不同时间尺度影响东亚冬季风的机制不一样,在百年尺度上可能太阳活动的作用越来越重要.

This study explored the effect of sea surface temperature (SST) on the interannual variations in wintertime haze days (WHDs) in the Pearl River Delta (PRD) region (WHD PRD ) of China. Analyses unravel that SST anomalies in the adjoining area of the northern Indian and Pacific sector (the NIP region) can drive the interannual variations in the frequency of wintertime haze over the PRD region, which is deemed a salient oceanic driver. The SST anomalies have a stable and significant anticorrelation with the interannual component of the WHD PRD . This anticorrelation is highest in the concurrent winter and thus exerts a strong influence on the variability of localized WHDs. Further observational and simulation results suggest that the cold SST anomalies in the NIP region can induce a large-scale east–west dipole pattern by triggering diabatic cooling to the northwest. This dipole resembles the pattern tied to a higher WHD PRD , with an anticyclonic anomaly centered over the Indo-China Peninsula and a cyclonic anomaly centered over the western North Pacific. Under such circumstances, the PRD region is dominated by consistent northerly wind anomalies, facilitating the formation of two crucial processes responsible for a higher WHD PRD : the northward transportation of aerosols and a decrease in local wet deposition.

From the perspectives of remote sensing and climatic factors like surface meteorological parameters, large‐scale atmospheric circulations, and external forcing factors (EFFs), the authors synthesize and review spatiotemporal variations of PM 2.5 over North China and how climate anomalies affect autumn and winter haze variability in North China according to recent studies. This review focuses on both interannual and interdecadal timescales. It is shown that circulations play an important role in influencing haze variability. Atmospheric circulations, which would be modulated by EFFs like sea surface temperature, sea ice, and snowpack, can affect the climate variability in haze over North China via modulation of surface‐layer parameters that are closely connected with the haze phenomenon. Therefore, EFFs are deemed significant factors impacting the climate variability of haze over North China, serving as paramount precursory signals for haze prediction. Furthermore, this paper suggests potential future research directions for haze variability studies in North China on the basis of summarizing and concluding the associated processes/mechanisms on how climatic factors affect haze variability, which could provide reference for treating and forecasting in situ hazy conditions.

基于1980-2017年京津冀地区定时观测资料、欧亚陆面积雪资料、欧洲中期天气预报中心(European Centre for Medium-range Weather Forecasts,ECMWF)再分析资料,美国国家环境预报中心/大气研究中心(NCEP/NCAR)再分析资料以及英国哈德莱中心提供的海冰密集度资料,分析了秋季10-11月京津冀霾日频数年际变率与同期欧亚积雪的物理联系,并通过气候统计诊断和敏感性试验探讨了积雪异常影响京津冀10-11月霾日频数年际变率的可能机理.结果 表明,10-11月京津冀霾日频数年际变率与同期东欧—西伯利亚平原地区(记为REu;50°～60°N,40°～80°E)积雪厚度和积雪覆盖度均呈现显著的正相关关系.REu积雪正异常与其西北侧的挪威海—巴伦支海海域以及北欧到东欧地区上空大气冷源密切联系,该冷源可激发一个自上述区域途经REu一直到东北亚的准正压大尺度纬向Rossby波列来调制影响京津冀霾日频数年际变率的关键环流系统,即东北亚异常反气旋.上述异常环流背景下,京津冀地区对流层低层为偏南风异常所控制,稳定大气层结易于建立,边界层高度偏低、地面风速偏弱且相对湿度偏高.该环境条件有利于霾天气发生发展,使得同期霾日偏多.作为预测信号,当前期9月楚科奇海—西波弗特海海冰偏少(多)时,10-11月京津冀霾日可能偏多(少).

The regional transport of air pollutants, controlled by emission sources and meteorological factors, results in a complex source–receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River middle basin (YRMB) of central China, experienced heavy air pollution characterized by hourly PM2.5 concentrations reaching 471.1 µg m−3 in January 2016. To investigate the regional transport of PM2.5 over central eastern China (CEC) and the meteorological impact on wintertime air pollution in the YRMB area, observed meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented noteworthy cases of heavy PM2.5 pollution in the YRMB area with unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion, and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer that are typically observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over CEC aggravated PM2.5 levels, thus creating heavy air pollution in the YRMB area. This demonstrates a source–receptor relationship between the originating air pollution regions in CEC and the receiving YRMB region. Furthermore, a backward trajectory simulation using a Flexible Particle dispersion (FLEXPART) Weather Research and Forecasting (WRF) model to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon season. It was estimated that the regional transport of PM2.5 from non-local air pollutant emissions contributes more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over China as a causative factor of heavy air pollution over the YRMB area.

Sub-seasonal variability in meridional activity of Western Pacific subtropical high (WPSH) exerts important influences on anomalous weather and climate in East Asian monsoon region. By using a sub-seasonal meridional index of the WPSH, the characteristics and atmospheric evolutions in association with the sub-seasonal meridional activity of the WPSH during boreal late summer are investigated. The meridional activity of the WPSH exhibits distinctive low frequency oscillation (LFO), with two dominant periods of 10-30 days and 40-50 days. The 10-30 days LFO is influenced by wave trains in mid-high latitudes and convection propagating from tropic. For the northward advance of the WPSH, in the high latitudes, teleconnection wave train originating from Atlantic Ocean propagates eastward, then the negative potential vortex anomalies enhance the high-level divergence in Northeast Asia. In the mid-latitudes, the 10-30 days low frequency wave train from North America propagates westward and influences the pressure field along the East Asia coast, whose energy is gained from the westerly jet through barotropic process. In the tropic, on time scale of 10-30 days, anomalous convections over the equatorial western Pacific propagate northwestward and trigger cyclone-anticyclone circulation anomalies along the East Asia coast, which in turn affect the meridional position of the WPSH. The 40-50 days LFO of meridional activity of WPSH is closely related to the convection anomalies under the interaction between Madden-Julian Oscillation (MJO) and monsoon intra-seasonal oscillation (MISO). The tropical MJO propagates eastward from the equatorial Indian Ocean to West Pacific and then propagates northward, in accompany with the northeastward propagation of anomalous convection teleconnection covering the tropical Indian Ocean-North Indian Peninsula-Northwest Pacific, resulting in the anomalous anti-cyclonic circulation over Northwest Pacific, which contributes to the northward advance of the WPSH. For the southward retreat of the WPSH, the contrary is the case in 10-30 days atmospheric LFO while relatively weaker 40-50 days atmospheric LFO does less contribution to the southward retreat of the WPSH.

The dynamic origin of the interannual variability of West China autumn rainfall (WCAR), a special weather/climate phenomenon over western-central China in September and October, was investigated via observational diagnosis and numerical simulations. Here we found that the interannual variability of WCAR is closely related to the local horizontal trough, which is passively induced by two lower-level anticyclonic (high pressure) anomalies over East Asia. The anticyclonic anomaly over the south is a Gill-type response to the central and eastern Pacific diabatic cooling, while that over the north is part of the mid- to high-latitude barotropic Rossby wave train, which could be induced by either the thermal forcing of the central and eastern Pacific Ocean sea surface temperature (SST) cooling or that of the subtropical northern Atlantic Ocean SST warming. The quasi-barotropic high pressure anomaly over East Asia acts as an “invisible mountain” that steers the low-level anomalous southwesterly into a southeasterly and hinders the water vapor going farther to the north, leading to enhanced WCAR. However, the real mountain ranges in the region (the Qinglin and Ba Mountains) have no essential impact on the formation and interannual variability of WCAR.

The North American continent, with its large terrain and being surrounded by oceans, does not provide the setup for a large-scale monsoon as we see in Asia. Here we examine the role of the southwards shift of the North American continent (140 degrees-50 degrees W, 20 degrees-80 degrees N) in determining North American monsoon (NAM) regions using the Community Atmosphere Model version 5.1. Results show that the meridional position of the North American continent plays a fundamental role in the existence of the NAM. When the North American continent is moved southwards to a certain latitude, most of the North American non-monsoon regions turn into monsoon regions, as strong and long-lasting surface sensible heating occurs from spring to summer, together with enhanced zonal land-sea thermal contrast. Thus, the low-level southerly wind and wind convergence are strengthened over the eastern side of the North American continent, resulting in a strong ascending motion in this region. On the other hand, the enhanced southerly wind and northwards equatorial airflow act to transport more moisture from the low-latitude oceans to the North American continent. As a result, the NAM circulation is strengthened, which is further maintained and developed via the "thermal adaptation" feedback.

回顾了南京信息工程大学(简称南信大)建校60年来季风研究的主要历程以及在亚洲季风,特别是在东亚季风研究方面取得的重要成果.20世纪80年代至21世纪初,中关季风合作、中日季风合作和“南海季风试验”3次国际季风合作研究的顺利实施,极大地推进了南信大季风研究团队的组建和壮大,同时也催生了一系列创新性成果.团队首先揭示了东亚季风与印度季风环流的差异,提出了东亚副热带季风的明确概念;发现了东亚副热带夏季风的建立独立并早于南海夏季风;揭示了“亚澳大陆桥”是北半球春季亚洲季风区对流最活跃的地区,其对流的建立和推进对东亚夏季风的建立至关重要;较早开展了东亚季风区季节内振荡北传特征和机制的研究并成功应用于东亚季风区延伸期预报.这些创新性成果的取得为季风研究做出了重要贡献.近年来,南信大秉承“开放发展、联合发展”的办学理念,大力引进高层次人才,进一步推动了季风研究.作为国际季风研究的重要力量之一,南信大季风研究团队将始终坚守季风研究阵地,不断深化季风理论认识、提升季风预测水平.

本文利用日本气象厅提供的历史海温资料、Hadley海温资料以及NCEP/NCAR再分析资料(1951～2010年)等探讨了东亚夏季风的强度与前期暖池热含量异常的关系.结果表明,西太平洋暖池热含量可以作为东亚夏季风强度的前期预测因子,两者正相关关系显著.本文选取相关系数更大、持续性更好的前期冬季暖池关键区(-5.5°～5.5°N;157.5°～170.5°E)热含量来进行预报.将暖池热含量指数和东亚夏季风指数均回归到夏季大气环流场上,发现在暖水年次年夏季西太副高偏弱、位置偏北,菲律宾以东以北洋面为气旋性环流,对流上升运动增强,赤道西太平洋地区为显著的西风距平,日本岛以东洋面为反气旋环流,对流下沉运动增强,日本岛以南、黄海至我国中东部地区为显著的东风距平,且前期2月西风带位置偏北,引起夏季海陆热力差异较大,最终导致东亚夏季风强度异常偏高;冷水年则相反.综上所述,当前期冬季西太平洋暖池热含量异常偏高(低)时,会造成次年东亚夏季风强度偏强(弱).

The present study investigates the diversity of the La Nina decaying phase and the corresponding spring and summer precipitation anomalies over the eastern China. Based on the differences in sea surface temperature anomaly (SSTA) evolution during the La Nina decaying phase, 18 La Nina events in the period 1961-2016 are classified into three types-namely, the persistent type (P-type), the re-intensified type (R-type), and the fast-decay type (F-type). Precipitation responses over eastern China during the decaying spring and summer of the three types of La Nina present significant differences. For the R-type La Nina decaying spring, the enhanced precipitation appears over northeastern China but significant suppressed precipitation anomalies are observed elsewhere, particularly in Yellow River basin, the Yangtze River basin, and southeastern China. Significant negative precipitation anomaly appears over northeastern China in both P-type and F-type La Nina decaying spring. In the decaying summer, for P-type La Nina, dry anomalies are apparent in southern and northern China. For R-type La Nina, negative rainfall anomalies are notable in northeastern China, the Hetao region, and the middle reaches of the Yangtze River basin. For F-type La Nina, significant negative rainfall anomalies are found over the Yangtze River basin and parts of northern China. The responses of the large-scale circulation anomalies to the distinct SSTA patterns of the different types of La Nina are responsible for the diversity of rainfall anomalies over eastern China. The precipitation anomaly pattern in eastern China is closely associated with the different types of La Nina decay, and it is seasonal-dependent. These two aspects should be taken into account when conducting seasonal predictions of spring and summer rainfall anomalies over eastern China using El Nino-Southern Oscillation as a predictor.