Analysis of climatic features and major meteorological disasters over the Three Gorges Region of the Yangtze River Basin in 2021

Based on daily observation data in the Three Gorges Region (TGR) of the Yangtze River Basin and global reanalysis data, the authors analyzed the climate characteristics and associated temporal variations in the main meteorological factors in 2021, as well as the year's climatic events and meteorological disasters. The 2021 average temperature was 0.2°C above the 1991–2020 average and the 13th-warmest year since 1961. Seasonally, winter and autumn were both warmer than usual. The annual mean precipitation was 12.8% above normal, and most regions experienced abundant rainfall throughout the year. The seasonal variation in precipitation was significant and the TGR had a wetter-than-normal spring and summer. The number of rainstorm days was higher than normal; the wind speed was above normal; and the relative humidity was higher than normal. In terms of rain acidity, 2021 was tied with 2020 as the lowest since 1999. From mid-September to early October 2021, the TGR experienced exceptional high-temperature weather, which was driven by abnormal activity of mid- and high-latitude atmospheric circulation over the Eurasian continent and the western Pacific subtropical high (WPSH). In addition, a strong blocking high over the Ural Mountains accompanied by intense mid-latitude westerly winds prevented cyclonic disturbances from extending to the subtropical region. As a result, under the combined effect of the weaker-than-normal cold-air activities and the anomalous WPSH, the TGR experienced extreme high-temperature weather during early autumn 2021.摘要本文分析了2021年长江三峡地区气候特征及主要天气气候事件. 2021年, 三峡地区年平均气温较常年偏高0.2°C, 降水量偏多12.8%, 年暴雨日数偏多, 年平均风速偏大, 年平均相对湿度偏高. 2021年与2020年同为有记录以来酸雨强度最弱年. 汛期区域强降水频发; 春季多低温阴雨; 秋冬寒潮过程降温幅度大影响广. 9月中旬至10月初, 三峡地区遭遇罕见“秋老虎”, 分析表明该时段内异常高温与中高纬度大气环流及西太平洋副热带高压活动异常等因子密切相关.     

State of the climate in the Three Gorges Region of the Yangtze River basin in 2020

2020年,长江三峡地区年平均气温17.2℃,接近常年;年平均降水量1530.8毫米,偏多29％,为1961年以来第二多,仅次于1998年.6月,7月降水量及年平均暴雨日数均为1961年以来第二多.平均风速较常年偏大;相对湿度略偏高;各月均无酸雨出现,近十余年酸雨强度呈现明显减弱趋势.2020年,三峡地区夏季暴雨洪涝灾...     

鲁南地区一次暴雨天气过程的数值模拟

利用常规观测资料以及中尺度数值模式的模拟结果,对2009年8月17—18日山东南部罕见暴雨天气过程成因进行了分析。结果表明:暴雨是受副热带高压、高空西风槽和地面倒槽共同影响产生的;低层强盛的偏南气流建立起水汽通道,把水汽源源不断地向暴雨区输送,同时山东上空低层高温高湿,能量升高,形成上干冷、下暖湿的对流性不稳定层结;强降水产生时,暴雨区上空存在较强的中β尺度系统,该系统具有强而窄的垂直上升运动、上下垂直的辐散辐合结构和强烈的对流不稳定等特征。     

The anthropogenic acceleration and intensification of flash drought over the southeastern coastal region of China will continue into the future

The frequent and rapid onset of flash drought poses a serious threat to agriculture and ecosystems. Detecting human influences on flash droughts and estimating their future risks under climate change have attracted great attention. Focusing on a record-breaking flash drought event in the southeastern coastal region of China in summer 2020, the authors found that the suppression of convective precipitation and high temperature caused by the persistent high geopotential height anomalies and land–atmosphere dry coupling were important reasons for the rapid onset and strong intensity of the flash drought. Event attribution analysis with the latest CMIP6 data showed that anthropogenic climate change has not only increased the likelihood of an onset speed and intensity like those of the 2020 flash drought event, by about 93% ± 20% and 18% ± 15%, respectively, but also increased the chance of their simultaneous occurrence, by about 86% ± 38%, according to their joint probability distribution. Under a business-as-usual future scenario (SSP2-4.5), the likelihood of such an onset speed, intensity, and their simultaneous occurrence will further increase, by 85% ± 33%, 49% ± 8%, and 81% ± 48%, respectively, as compared with current climate conditions. This study highlights the importance of anthropogenic climate change for accelerating and intensifying flash drought in the southeastern coastal region of China.摘要快速爆发的骤旱对农业生产, 生态环境等造成严重威胁, 亟须量化当前及未来气候变化对骤旱爆发过程的影响. 2020年夏季, 在持续高压异常和陆气干耦合的控制下, 我国东南沿海地区出现高温少雨天气并引发极端骤旱事件. 基于第六次国际耦合模式比较计划 (CMIP6) 数据开展归因分析, 本文发现相比天然情景, 温室气体排放等人为因子导致的气候变化不仅使类似2020年骤旱爆发速度和强度的发生概率分别增加93%和18%, 还使其联合概率增加86%. 在目前排放水平下, 此类骤旱爆发速度和强度发生概率及其联合概率在21世纪末将提高85%, 49%, 和81%, 极大增加了干旱适应的挑战.     

Effects of spring Arctic sea ice on summer drought in the middle and high latitudes of Asia

Based on data observed from 1979 to 2017, the influence of Arctic sea ice in the previous spring on the first mode of interannual variation in summer drought in the middle and high latitudes of Asia (MHA) is analyzed in this paper, and the possible associated physical mechanism is discussed. The results show that when there is more sea ice near the Svalbard Islands in spring while the sea ice in the Barents–Kara Sea decreases, the drought distribution in the MHA shows a north–south dipole pattern in late summer, and drought weakens in the northern MHA region and strengthens in the southern MHA region. By analyzing the main physical process affecting these changes, the change in sea ice in spring is found to lead to the Polar–Eurasian teleconnection pattern, resulting in more precipitation, thicker snow depths, higher temperatures, and higher soil moisture in the northern MHA region in spring and less precipitation, smaller snow depths, and lower soil moisture in the southern MHA region. Such soil conditions last until summer, affect summer precipitation and temperature conditions through soil moisture–atmosphere feedbacks, and ultimately modulate changes in summer drought in the MHA.摘要本文分析了亚洲中高纬度地区 (MHA) 年际尺度夏季干旱的主模态时空变化特征, 以及影响第一模态的主要影响因子和可能的物理过程. 结果显示该区域夏季干旱第一模态主要呈现一个南北偶极性的分布. 而影响MHA夏季干旱的主要影响因子为前春北极海冰. 当春季斯瓦尔巴群岛附近海冰偏多, 而巴伦支海-喀拉海海冰减少时, 通过冰-气相互作用, 使得MHA北部春季降水增加, 雪深加厚, 土壤湿度偏高, 而南部则相反. 然后这样的土壤湿度条件从春季持续到夏季, 通过土壤湿度-大气反馈影响夏季MHA降水和温度变化, 最终对夏季干旱主模态产生影响.     

The increasing predominance of extreme precipitation in Southwest China since the late 1970s

Extreme precipitation events cause severe environmental and societal damage worldwide. Southwest China (SWC) is sensitive to such effects because of its overpopulation, underdevelopment, and fragile ecosystems. Using daily observations from 108 rain-gauge stations, the authors investigated the frequency of extreme precipitation events and their contribution to total precipitation in SWC since the late 1970s. Results indicate that total precipitation is decreasing insignificantly, but rainfall-events frequency is decreasing significantly, whereas the region is experiencing more frequent and intense extreme precipitation events. Note that although fewer stations are statistically significant, about 60% of the rain-gauge stations show an increasing trend in the frequency and intensity of extreme precipitation. Furthermore, there is an increasing trend in the contribution of total extreme precipitation to total precipitation, with extreme precipitation becoming dominant in the increasingly arid SWC region. The results carry important implications for policymakers, who should place greater emphasis on extreme precipitation and associated floods and landslides when drafting water-resource management policies.摘要本文分析了中国西南20世纪70年代末以来极端降水事件的频率, 强度及其对总降水的贡献. 结果表明, 该地区约60%的降水站点极端降水的频率和强度正在增加, 而大多数站点总降水频率明显减少. 同时极端降水总量对总降水量的贡献有显著增加的趋势, 极端降水在日益干旱的中国西南地区变得更具主导性. 研究结果提醒应更加重视极端降水及其可能引发的次生灾害, 如洪水, 山体滑坡等.     

FY-2/D卫星反演的云特征参数与地面降水的相关分析

利用中国气象局人工影响天气中心研发的云参数卫星反演系统反演得到的产品,结合地面自动站观测资料,对2009年9月19—20日降水过程的云参数及地面雨量进行对比分析。结果发现:云顶高度、云顶温度、过冷层厚度和云光学厚度对本次降水过程指示性不强,而云粒子有效半径及云液水路径对降水有较好的指示作用,且云液水路径指示作用更强,二者的变化超前于地面降水30min到1h;云液水路径及云粒子有效半径大值区与地面雨量的大小呈正相关,云液水路径值大于400g.m-2及云粒子有效半径大于27μm区域与地面雨强中心位置基本一致。掌握云参数的演变规律,有助于监测、识别大范围人工影响天气作业条件和分析可播区。     

An overview of soil moisture drought research in China: Progress and perspective

Soil moisture drought (SMD) directly affects agricultural yield and land water resources. Understanding and predicting the occurrences and evolution of SMD are of great importance for a largely agricultural country such as China. Compared to other drought categories, SMD receives less attention due to the lack of long-term soil moisture datasets. In recent decades, SMD research has been greatly developed in China, benefiting from increased ground and satellite measurements along with state-of-the-art land surface models. Here, the authors provide a brief overview of the recent progress in SMD research in China, focus on historical drought identification and its prediction, and then raise some future perspectives. Based on historical SMD studies, drought frequency has increased overall and drought duration has been prolonged since the 1950s for China as a whole, but they both show substantial temporal variations at the regional scale. Research on SMD prediction has mainly relied on the statistical relationship between soil moisture and climate variables. Few studies based on the dynamical approach in seasonal drought prediction have highlighted the importance of initial conditions and atmospheric forcing datasets. Given the importance of SMD in agricultural practice and water resource management in China, it is necessary to emphasize the following: 1) conducting research on multiple time scales (e.g., from days to the centurial time scale) and cross-regional drought identification research; and 2) developing a SMD prediction system that takes advantage of climate prediction systems, land surface models, and multisource soil moisture datasets.摘要论文回顾了中国土壤湿度干旱 (SMD) 历史重建和季节预测研究进展, 并对未来研究进行了展望. 自1950s年代以来, 全国整体干旱频率增加, 持续时间延长, 且有明显区域特征. SMD预测多是利用土壤湿度与气候变量之间的统计关系, 而少量基于动力学方法的干旱预测研究强调了初始条件和大气强迫数据对季节尺度干旱预测的重要性. 本论文提出: 1) 加强多时间尺度, 跨区域的SMD研究; 2)联合气候预测系统, 陆面模式和多源土壤湿度数据研制SMD预测系统.     

Strong heatwaves with widespread urban-related hotspots over Africa in 2019

2019 was one of the hottest years in recent decades, with widespread heatwaves over many parts of the world, including Africa. However, as a developing and vulnerable region, the understanding of recent heatwave events in Africa is limited. Here, the authors incorporated different climate datasets, satellite observations, and population estimates to investigate patterns and hotspots of major heatwave events over Africa in 2019. Overall, 2019 was one of the years that experienced the strongest heatwaves in terms of intensity and duration since 1981 in Africa. Heatwave hotspots were clearly identified across western-coastal, northeastern, southern, and equatorial Africa, where major cities and human populations are located. The proportion of urban agglomerations (population) exposed to extreme (99th percentile) heatwaves in the Northern Hemisphere and Southern Hemisphere rose from 4% (5 million people) and 15% (17 million people), respectively, in the baseline period of 1981–2010 to 36% (43 million people) and 57% (53 million people), respectively, in 2019. Heatwave patterns and hotspots in 2019 were related to anomalous seasonal change in atmospheric circulation and above-normal sea surface temperature. Without adaptation to minimize susceptibility to the effects of heatwave events, the risks they pose in populated areas may increase rapidly in Africa.摘要2019 年是近几十年来最热的年份之一, 包括非洲在内的全球许多地区都受到大范围的热浪侵袭. 然而, 非洲作为脆弱的发展中地区, 我们对其近年热浪事件的了解非常有限. 本研究中, 我们结合了不同的气候数据集, 卫星观测资料和人口数据, 研究了 2019 年非洲地区主要热浪事件发生的时空特征和热点分布区. 总体而言, 2019 年是非洲地区自 1981 年以来热浪强度最强, 持续时间最久的年份之一. 在主要城市和人口所在的非洲西海岸, 东北部, 南部和赤道地区是热浪发生的热点区. 位于赤道以北的非洲地区, 暴露于极端 (第 99 个百分位) 热浪的城市人口比例从 1981–2010 年基准期的 4% (500 万人) 上升至2019 年的 36% (4300 万人). 位于赤道以南地区, 暴露于极端热浪的城市人口则从基准期的15% (1700 万人) 上升至57% (5300 万人). 2019 年的热浪时空特征和热点分布与大气环流的季节变化异常和海温的暖异常有关. 如果不及时采取适应措施以尽量减少人口对热浪事件影响的敏感性, 热浪对非洲人口稠密地区构成的风险可能会迅速增加.     

Observed decadal shifts and trends in global tropical cyclone activities from 1980 to 2021

This study investigates the variability of annual tropical cyclone (TC) frequency and intensity over six major ocean basins from 1980 to 2021. Statistical change-point and trend analyses were performed on the TC time series to detect significant decadal variation in TC activities. In the middle of the last decade of the 20th century, the frequency of TC genesis in the North Atlantic basin (NA) and North Indian Ocean (NIO) increased dramatically. In contrast, the frequency in the western North Pacific (WNP) decreased significantly at the end of the century. The other three basins—the East Pacific, southern Indian, and South Pacific—all experienced a declining trend in annual TC frequency. Over recent decades, the average TC intensity has decreased in the East Pacific and the NA, whereas it has risen in the other ocean basins. Specifically, from 2013 to 2021, the average peak TC intensity in the NIO has enhanced significantly. The magnitude of the Genesis Potential Index exhibits fluctuation that is consistent with large-scale parameters in the NIO, NA, and WNP, emphasizing the enhancing and declining trends in TCs. In addition, a trend and correlation analysis of the averaged large-scale characteristics with TCs revealed significant associations between the vertical wind shear and TC frequency over the NIO, NA, and WNP. Therefore, global TC trends and decadal variations associated with environmental parameters deserve further investigation in the future, mainly linked to the significant climate modes.摘要研究发现在1980–2021期间全球6个海域每年热带气旋的发生频次和强度具有显著年代际变化规律, 最近几十年, 北大西洋和北印度洋的热带气旋发生频次明显增加, 但西北太平洋的热带气旋却显著下降. 另外三个海域, 东太平洋, 南印度洋和南太平洋发现所生成的热带气旋有减少趋势. 但在过去十几年, 平均热带气旋的强度除了在东太平洋和北大西洋有所减弱但在其他几个海域有所加强, 特别是在 2013–2021期间, 北印度洋的平均热带气旋的强度增强明显. 热带气旋的潜在生成指数 (GPI) 增加或减少趋势变化与北印度洋, 北大西洋和西太平洋热带气旋变化相关的大尺度环流一致. 另外, 北印度洋, 北大西洋和西太平洋上空的垂直风切变是影响其区域热带气旋发生频次变化的主要因子, 不同的气候模态也可能对全球热带气旋的趋势变化和年代际变化有影响, 值得进一步研究.     

Strengthened influence of the East Asian trough on spring extreme precipitation variability over eastern Southwest China after the late 1980s

The relationship between variations in the East Asian trough (EAT) intensity and spring extreme precipitation over Southwest China (SWC) during 1961–2020 is investigated. The results indicate that there is an interdecadal increase in the relationship between the EAT and spring extreme precipitation over eastern SWC around the late 1980s. During the latter period, the weak (strong) EAT corresponds to a strong and large-scale anomalous anticyclone (cyclone) over the East Asia–Northwest Pacific region. The EAT-related anomalous southerlies (northerlies) dominate eastern SWC, leading to significant upward (downward) motion and moisture convergence (divergence) over the region, providing favorable (unfavorable) dynamic and moisture conditions for extreme precipitation over eastern SWC. In contrast, during the former period, the EAT-related circulation anomalies are weak and cover a relatively smaller region, which cannot significantly affect the moisture and dynamic conditions over eastern SWC; therefore, the response in extreme precipitation over eastern SWC to EAT is weak over the period. The interdecadal change in the relationship between eastern SWC spring extreme precipitation and the EAT could be related to the interdecadal change in the EAT variability. The large (small) variability of the EAT is associated with significant (insignificant) changes in spring extreme precipitation over eastern SWC during the latter (former) period.摘要本文研究表明东亚大槽强度与中国西南地区东部春季极端降水的关系在20世纪80年代末后显著增强, 这可能与东亚大槽自身变率的年代际变化有关. 在80年代末之后, 东亚大槽的变率显著增强, 其对应的大气环流异常也偏强, 范围偏大, 可以显著影响西南地区东部的水汽和动力条件, 从而引起该地区春季极端降水的显著变化. 而在80年代末之前, 东亚大槽的变率偏弱, 其对应的大气环流异常也偏弱, 范围偏小, 因此不能对西南地区东部春季极端降水的变化产生显著影响.     

The impacts of the East Asian subtropical westerly jet on weather extremes over China in early and late summer

Summer weather extremes (e.g., heavy rainfall, heat waves) in China have been linked to anomalies of summer monsoon circulations. The East Asian subtropical westerly jet (EASWJ), an important component of the summer monsoon circulations, was investigated to elucidate the dynamical linkages between its intraseasonal variations and local weather extremes. Based on EOF analysis, the dominant mode of the EASWJ in early summer is characterized by anomalous westerlies centered over North China and anomalous easterlies centered over the south of Japan. This mode is conducive to the occurrence of precipitation extremes over Central and North China and humid heat extremes over most areas of China except Northwest and Northeast China. The centers of the dominant mode of the EASWJ in late summer extend more to the west and north than in early summer, and induce anomalous weather extremes in the corresponding areas. The dominant mode of the EASWJ in late summer is characterized by anomalous westerlies centered over the south of Lake Baikal and anomalous easterlies centered over Central China, which is favorable for the occurrence of precipitation extremes over northern and southern China and humid heat extremes over most areas of China except parts of southern China and northern Xinjiang Province. The variability of the EASWJ can influence precipitation and humid heat extremes by driving anomalous vertical motion and water vapor transport over the corresponding areas in early and late summer.摘要东亚副热带西风急流是影响中国极端天气的重要原因之一, 然而之前的研究主要关注整个夏季急流的变率, 对其早夏和晚夏变率的区别及其对极端天气的影响关注较少. 本文研究了早夏和晚夏东亚副热带西风急流季节内变化特征的区别, 以及这种区别带来的极端天气的差异及其可能的动力学机制. 研究结果表明, 相比于早夏, 晚夏急流季节内变化中心位置偏西偏北, 通过改变垂直运动和水汽输送可以影响极端降水和湿热浪在相应区域的发生概率.     

Response of extreme precipitation to increasing extratropical cyclonic vortex frequency

Since the 2000s, extratropical extremes have been more frequent, which are closely related to anomalies of planetary-scale and synoptic-scale systems. This study focuses on a key synoptic system, the extratropical cyclonic vortex (ECV) over land, to investigate its relations with extreme precipitation. It was found that ECVs have been more active post-2000, which has induced more extreme precipitation, and such variation is projected to persist along with increasing temperature within 1.5°C of global warming. An enhanced quasi-stationary vortex (QSV) primarily contributes to the ECV, rather than inactive synoptic-scale transient eddies (STEs). Inactive STEs respond to a decline in baroclinicity due to the tendency of the homogeneous temperature gradient. However, such conditions are helpful to widening the westerly jet belt, favoring strong dynamic processes of quasi-resonant amplification and interaction of STEs with the quasi-stationary wave, and the result favors an increasing frequency and persistence of QSVs, contributing to extreme precipitation.摘要自21世纪以来, 热带外极端降水频次增加. 随着中高纬度的显著增温, 经向温度梯度减弱导致低层大气斜压性减小, 由此产生的气旋型瞬变涡天气系统等活动减弱. 然而, 热力分布导致西风急流带变宽, 经向环流加大, 有助于行星尺度波动相关的涡旋异常增加, 如东北冷涡, 中亚涡, 东欧-地中海涡, 北美涡等, 进而增加了气旋涡影响范围的极端降水频次. 在未来变暖背景和1.5°C增温的目标内, 热带外气旋涡增强会进一步促进极端降水发生.     

Strengthening the three-dimensional comprehensive observation system of multi-layer interaction on the Tibetan Plateau to cope with the warming and wetting trend

Changes in the water cycle on the Tibetan Plateau (TP) have a significant impact on local agricultural production and livelihoods and its downstream regions. Against the background of widely reported warming and wetting, the hydrological cycle has accelerated and the likelihood of extreme weather events and natural disasters occurring (i.e., snowstorms, floods, landslides, mudslides, and ice avalanches) has also intensified, especially in the high-elevation mountainous regions. Thus, an accurate estimation of the intensity and variation of each component of the water cycle is an urgent scientific question for the assessment of plateau environmental changes. Following the transformation and movement of water between the atmosphere, biosphere and hydrosphere, the authors highlight the urgent need to strengthen the three-dimensional comprehensive observation system (including the eddy covariance system; planetary boundary layer tower; profile measurements of temperature, humidity, and wind by microwave radiometers, wind profiler, and radiosonde system; and cloud and precipitation radars) in the TP region and propose a practical implementation plan. The construction of such a three-dimensional observation system is expected to promote the study of environmental changes and natural hazards prevention.摘要青藏高原的水循环变化对于高原及其下游区域人类的生产生活具有举足轻重的影响. 在高原暖湿化的背景下, 其水文循环加快, 极端天气和自然灾害事件概率增大, 比如, 雪灾, 洪水, 滑坡, 泥石流, 冰崩在山区频发. 因此, 如何准确的估算青藏高原水循环各分量的大小及变化幅度是评估高原环境变化影响亟需解决的科学问题. 根据水在各圈层间转换过程, 我们提出了建立第三极地区 (尤其是复杂山区) 的三维立体多圈层地气相互作用综合观测系统(包括涡动相关系统, 行星边界层塔, 微波辐射计, 风廓线仪和无线电探空系统观测的风温湿廓线及云雨雷达等)的紧迫性和具体方案, 进而为研究青藏高原环境变化和山区灾害预测服务.     

3D DBSCAN detection and parameter sensitivity of the 2022 Yangtze river summertime heatwave and drought

Spatially and temporally accurate event detection is a precondition for exploring the mechanisms of climate extremes. To achieve this, a classical unsupervised machine learning method, the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) clustering algorithm, was employed in the present study. Furthermore, the authors developed a 3D (longitude–latitude–time) DBSCAN-based workflow for event detection of targeted climate extremes and associated analysis of parameter sensitivity. The authors applied this 3D DBSCAN-based workflow in the detection of the 2022 summertime Yangtze extreme heatwave and drought based on the ERA5 reanalysis dataset. The heatwave and drought were found to have different development and migration patterns. Synoptic-scale heatwave extremes appeared over the northern Pacific Ocean at the end of June, extended southwestwards, and covered almost the entire Yangtze River Basin in mid-August. By contrast, a seasonal-scale drought occurred in mid-July over the continental area adjacent to the Bay of Bengal, moved northeastwards, and occupied the entire Yangtze River Basin in mid-September. Event detection can provide new insight into climate mechanisms while considering patterns of occurrence, development, and migration. In addition, the authors also performed a detailed parameter sensitivity analysis for better understanding of the algorithm application and result uncertainties.摘要极端气候事件的精准识别是机理分析的重要前提. 本研究借助无监督机器学习中经典的DBSCAN密度聚类算法, 发展了在三维 (经度-纬度-时间) 空间内进行目标事件识别和参数敏感性分析的研究方案. 在2022年长江全域高温伏秋旱事件识别中的应用表明, 本次天气尺度极端热浪和季节尺度重旱事件的产生发展, 空间传播模式不同. 天气尺度热浪信号自6月底从北太平洋向西南方向延伸, 直至8月中旬覆盖长江全域; 季节重旱信号于7月中旬从孟加拉湾陆面区域向东北向延伸, 直至9月中旬覆盖长江全域. 同时, 本研究中亦进行了相关参数敏感性的详细分析, 对算法应用, 结果理解亦有帮助.     

The exceptionally strong and persistent Arctic stratospheric polar vortex in the winter of 2019–2020: 2019-2020冬季北半球超强极涡事件

The Arctic stratospheric polar vortex was exceptional strong, cold and persistent in the winter and spring of 2019–2020. Based on reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research and ozone observations from the Ozone Monitoring Instrument, the authors investigated the dynamical variation of the stratospheric polar vortex during winter 2019–2020 and its influence on surface weather and ozone depletion. This strong stratospheric polar vortex was affected by the less active upward propagation of planetary waves. The seasonal transition of the stratosphere during the stratospheric final warming event in spring 2020 occurred late due to the persistence of the polar vortex. A positive Northern Annular Mode index propagated from the stratosphere to the surface, where it was consistent with the Arctic Oscillation and North Atlantic Oscillation indices. As a result, the surface temperature in Eurasia and North America was generally warmer than the climatology. In some places of Eurasia, the surface temperature was about 10 K warmer during the period from January to February 2020. The most serious Arctic ozone depletion since 2004 has been observed since February 2020. The mean total column ozone within 60°–90°N from March to 15 April was about 80 DU less than the climatology.摘要2019-2020冬季北极平流层极涡异常并且持续的偏强,偏冷.利用NCEP再数据和OMI臭氧数据, 本文分析了此次强极涡事件中平流层极涡的动力场演变及其对地面暖冬天气和臭氧低值的影响.此次强极涡的形成是由于上传行星波不活跃.持续的强极涡使得2020年春季的最后增温出现时间偏晚.平流层正NAM指数向下传播到地面, 与地面AO指数和NAO指数相一致, 欧亚大陆和北美地面气温均比气候态偏暖, 在欧亚大陆的一些地区, 2020年1月和2月的气温甚至偏高了10K.2020年2月以来北极臭氧出现了2004年以来的最低值, 2020年3-4月60°–90°N的平均臭氧柱总量比气候态偏低了80DU.     

Impacts of ENSO on wintertime PM2.5 pollution over China during 2014–2021

China has implemented a series of emission reduction policies since 2013, and the concentration of air pollutants has consequently decreased significantly. However, PM_2.5 (particulate matter with an aerodynamic diameter less than 2.5 µm) pollution still occurs in China in relation to the interannual variations in meteorological conditions. Considering that El Niño–Southern Oscillation (ENSO) is the strongest signal modulating the interannual variation in the atmosphere–ocean system, in this study the authors investigate the variations in PM_2.5 concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021. Results show that the wintertime PM_2.5 concentrations in the Beijing–Tianjin–Hebei and Fenwei Plain regions during El Niño years are higher than those during La Niña years, which can be explained by the anomalous southerly (northerly) winds during El Niño (La Niña) favoring PM_2.5 accumulation (diffusion). In the Pearl River Delta region, PM_2.5 concentrations decrease in El Niño relative to La Niña years owing to the enhanced water vapor flux and precipitation, removing more PM_2.5 from the atmosphere. The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_2.5 over the Yangtze River Delta region, which should be analyzed case by case.摘要2013年以来中国实施了一系列减排政策, 大气污染物浓度明显下降, 但由于气象条件的年际变化, 中国PM_2.5 (空气动力学直径小于2.5 µm的颗粒物) 污染仍然存在. 厄尔尼诺–南方涛动 (ENSO) 是调节大气–海洋系统年际变化的最强信号. 本文研究了2014–2021年四次ENSO事件期间, 中国四个特大城市群冬季PM_2.5浓度的变化. 结果表明, 在京津冀和汾渭平原地区, 由于厄尔尼诺 (拉尼娜) 期间的偏南风 (偏北风) 异常有利于 PM_2.5 的积累 (扩散), 冬季PM_2.5浓度在厄尔尼诺年高于拉尼娜年. 在珠三角地区, 由于厄尔尼诺冬季水汽通量和降水的增加有利于大气中PM_2.5的湿清除, 冬季PM_2.5浓度在厄尔尼诺年低于拉尼娜年. 在环流和降水异常的综合作用下, ENSO对长三角地区PM_2.5浓度的影响难以预测, 应逐案分析.     

The development of a powerful Mongolian cyclone on 14–15 March 2021: Eddy energy analysis

Intense and extensive dust, caused by a strong Mongolian cyclone, hit Mongolia and northern China on 14–15 March 2021. In this study, the development process of this cyclone is analysed from the perspective of high-frequency eddy energetics. During the low-frequency circulation field of early March of 2021, an amplified polar vortex intruding towards central Asia and a ridge straddling eastern and northeastern Asia worked in concert to comprise a strong baroclinic zone from central Asia to Lake Baikal. Under these favourable conditions, on 13 March, a migratory trough triggered the Mongolian cyclone by crossing over the Sayan Mountains. The downwards transfer of kinetic energy from the eddy at 850 hPa played a key role in the intensification and mature stage of the cyclone. This mechanism was primarily completed by the cold air sinking behind the cold front. The frontal cyclone wave mechanism became crucial once the cyclone started to rapidly develop. The authors emphasize that the anomalously large growth of high-frequency available potential energy, which characterized this super strong cyclone, was obtained by extracting energy first from the time-mean available potential energy and then from the low-frequency available potential energy. The interannual temperature anomaly pattern of “north cold south warm” facilitated the additional time-mean available potential energy, and the temperature anomaly pattern of “northwest cold southeast warm” conditioned the extra low-frequency available potential energy. The analysis results suggest that the interaction between high- and low-frequency waves was also important in the development of the intense cyclone.摘要2021年3月14-15日, 强蒙古气旋引起的大范围强沙尘天气袭击了蒙古国和中国北方地区. 本文从高频涡动能量学的角度分析了这一超强气旋的发展过程. 2021年3月初, 加强的极涡向中亚伸入, 并与横跨东亚和东北亚的一个大型脊协同作用, 由此形成了从中亚到贝加尔湖地区的强大斜压带. 在这一有利的低频环流条件下, 3月13日一个移动性小槽越过萨彦岭后触发了蒙古气旋. 850 hPa涡旋动能的下传在气旋的加强和成熟阶段起到了关键作用. 而这一机制主要由冷锋后侧的冷空气下沉过程完成. 一旦气旋开始快速发展, 锋面气旋波机制就变得至关重要.我们强调, 高频涡动有效位能是首先从时间平均有效势能中提取能量, 然后从低频有效位能中汲取能量而剧烈增长的, 这正是该超强气旋的鲜明特征. “北冷南暖”的近地面温度气候异常型为时间平均有效位能的增多和向高频涡动有效位能的转换提供了条件, 而“西北冷东南暖”的温度异常型则有利于低频有效位能的增加和向高频涡动有效位能的转换. 分析结果表明, 高低频波之间的相互作用对蒙古气旋的增强也很重要.     

Mechanisms governing the evolution of a long-lived northwest vortex that caused a series of disasters in Northwest China

西北涡是我国西北地区一类发生频率较高的中尺度涡旋,其所引发灾害的强度与西南低涡,高原涡相当,但相关研究却远远少于前两种涡旋.为了深化对西北涡的认识,本文利用水汽与环流收支对一次长生命史西北涡(其在西北地区引发了一系列暴雨过程,导致了严重的输电线路故障与城市内涝)进行了研究,发现,东海与渤海是此西北涡引发暴雨的主要水汽来...