郑州“7·20”极端暴雨过程中水汽和高低空急流作用机制的数值模拟

针对郑州“7·20”特大暴雨过程,使用CMA-MESO区域模式对此次极端强降水过程中水汽与高低空急流的影响进行了数值试验分析。结果表明,此次暴雨过程较为成功地被中尺度模式模拟再现;暴雨过程中水汽来源主要为台风“烟花”北侧的东南急流携带的来自西太平洋与印度洋的水汽以及台风“查帕卡”北侧东南气流携带的来自南海的水汽;降水及水汽输送对水汽含量十分敏感,水汽含量微小的变化便会使郑州上空气流辐合区强度减弱,水汽累积减少,降水范围向河南北部缩小,降水强度大幅度减弱;低空急流对应的气流辐合区是郑州上空出现强垂直上升运动中心的主要机制,低空急流减弱后,水汽辐合减弱,降水减少,降水中心位置偏西南,高空急流对降水的影响与低空急流相比较小。     

台风“玲玲”对黑龙江暴雨影响分析

选取2019年9月7-8日NCEP/NCAR(1°×1°)再分析资料,分析了降水实况、卫星云图、环流形势、物理量场。结果表明:此次暴雨过程主要受台风登陆后减弱的热带风暴影响,副热带高压的维持为水汽的输送与台风的北进起到了促进作用,台风外围水汽成为此次降水的主要水汽来源,高低空急流耦合加强了动力条件,暴雨落区与高空急流的右侧、低空急流的左侧、垂直运动强上升区及水汽通量散度辐合区有较高的吻合度。     

地形高度对暴雨过程的热力和水汽条件影响数值模拟试验

利用NCEP再分析资料和WRF模式,对2014年8月31日重庆市云阳县特大暴雨进行形势分析和数值模拟,针对重庆地区地形设计了三组地形敏感性试验,分析地形改变对暴雨过程热力条件和水汽条件的影响。结果表明:低纬地区不稳定能量大量积聚并向北传播,在地形和急流的垂直扰动触发下,对流强烈发展;850 h Pa低空急流将来自南海的水汽输送至重庆地区,水汽低层辐合、高层辐散形成的抽吸作用引发水汽的垂直输送。大巴山高度降低后,不稳定厚度减小导致对流强度明显降低;阻挡作用降低不利于水汽在暴雨区的汇聚;水汽辐合、辐散的强度降低导致水汽的垂直输送强度明显减弱。齐岳山高度降低后,低空急流所引起的垂直扰动位置偏南导致高能舌和对流活动位置偏南;水汽输送中心南压,水汽通道变宽导致暴雨区上空水汽输送减弱;低空急流位置偏南导致其所引起的水汽辐合时间偏晚。     

“丹娜丝”台风对“菲特”台风影响期间浙北特大暴雨作用的数值研究

利用自动站、NCEP再分析等资料和WRF模式对1323号"菲特"台风影响期间的浙北特大暴雨过程中"丹娜丝"的作用进行了数值研究。数值模拟和剔除"丹娜丝"台风的数值敏感试验表明,没有"丹娜丝"台风存在,浙北暴雨中心基本消失。此次暴雨过程中"丹娜丝"作用,是相当于一个水汽源,通过其存在有利于建立和维持暴雨区东侧强急流通道,源源不断将其水汽向暴雨区输送,作用占到2/3强,水汽丰富的东风急流和登陆后减弱的"菲特"东南气流在低层汇合形成较强的辐合,激发中小尺度对流系统和雨带的发生发展,对暴雨的触发和维持都做出了重要的贡献。     

河北一次春季回流暴雨过程及其热力结构分析

利用常规观测资料和NCEP 1°×1°再分析资料,采用天气动力学诊断方法,对河北中南部春末一次回流暴雨的风场、水汽、热力条件进行了详细分析。结果表明:(1)此次大暴雨发生在地面冷锋后部、近地层超低空急流产生回流的稳定气团中,850—700 hPa低空西南急流和切变线是其主要影响系统。(2)随高空急流发展,急流中心右前方强辐合引起气流下沉,使低层高压加强、高压南部风速加大,导致山东、河北南部低空东北风加强而产生近地面层超低空东北风急流,与其上层偏南急流相遇在太行山东麓产生耦合形成回流,有利于在河北南部、山东等地形成暴雨中心。(3)强暴雨发生在西南水汽通道北侧边缘,暴雨区水汽主要为西南急流输送;强暴雨区位于水汽通量散度强辐合区与水汽通量散度强辐散区之间的水汽通量散度锋区中,低层风切变辐合对暴雨触发起到关键作用。     

台风“威马逊”登陆后长时间维持原因分析

超强台风威马逊(1409)在华南三次登陆,登陆后减弱缓慢,带来了狂风暴雨和巨大的经济损失。利用NCEP再分析资料、CMABST最佳台风路径数据等资料,对"威马逊"长时间维持的原因进行天气学和动力学诊断分析,结果表明:(1)500hPa副高西伸发展,紧随着台风,副高和台风环流之间维持较强的气压梯度和水汽输送,有利于台风环流的维持。850hPa西南季风急流和越赤道气流合并卷入台风低压环流中,输送的水汽和不稳定能量是台风在登陆后衰减缓慢的重要原因。高空存在强流出气流,高层辐散抽吸作用有利于台风强度的维持和发展。(2)台风移向下游区域海温偏高、环境风垂直切变小、强盛水汽输送是台风强度维持的重要环境条件。台风登陆后涡度和垂直速度结构完整,减弱缓慢,利于台风环流的维持。台风移入的华南地区处于热力不稳定状态,有利于对流凝结潜热效率的增加和台风环流内对流活动的增强,从而有利于台风强度的维持。     

中低纬度环流系统的相互作用及其暴雨特征的模拟研究

利用MM5模式分别模拟了台风、中纬度西风槽对台风远距离槽前降水的影响.试验结果表明,(1)台风的强度影响了台风东侧东南急流向中纬度槽前的水汽输送.低层水汽输送,造成中纬度暴雨区强水汽辐合和不稳定能量积聚,故槽前降雨的强度与其南方台风东侧的水汽输送有着相当密切的关系.(2)中纬度西风槽提供了有利于台风远距离降水的大尺度背景场.西风槽的存在,有利于垂直运动的发展和维持,有利于降雨的产生和发展.模拟结果表明,槽的加强和减弱将会相应地造成中纬度暴雨区的加强和减弱.     

台风“韦森特”登陆后暴雨的成因分析

采用常规气象资料、区域自动站资料以及NCEP/NCAR分辨率1°×1°再分析资料,对2012年1208号台风"韦森特"登陆影响下,珠江三角洲和粤西地区的暴雨过程进行分析。分析了"韦森特"登陆后的高低空环流形势和辐合辐散场、西南季风的活动以及水汽输送情况。结果表明:1)西太副高高压脊西伸加强,且脊线位置维持,抑制了"韦森特"的北上,有利于其登陆后移速不致过快,为"韦森特"西北西行过程中产生持续性暴雨提供了稳定的背景场。2)100°E附近、108°E附近两支越赤道气流及索马里急流的加强,使西南季风进一步发展,为台风登陆后的降水补充大量水汽、热量和动量,有利于其降水发生维持。同时,水汽输送大值带穿过中南半岛,源源不断地向台风环流输送水汽。随着台风登陆后西北移动和西风大值区北抬的影响,水汽通量大值区和水汽通量散度大值区相应北抬,对暴雨增幅的发生有一定的作用。3)台风登陆后,高空辐散明显加强,强于低层辐合,高层流出的气流具有强的抽吸作用,为强降水的发生提供了动力抬升条件。     

“西马仑”与“海贝思”台风特大暴雨对比分析

利用常规气象观测资料、NCEP再分析资料、卫星云图和雷达回波等资料,采用多种物理量诊断分析方法,对路径相似、在闽南地区产生特大暴雨的1308号台风"西马仑"和1407号台风"海贝思"的环流形势特征、云系结构特征及水汽、动力、热力条件进行了对比分析。结果表明:"西马仑"的过程特点是雨强大、降水时间集中,而"海贝思"的特点则是雨强小、降水时间长;"西马仑"云系结构紧密,属中尺度对流云团降水,而"海贝思"云系结构松散,其外围的螺旋云带产生的列车效应是产生特大暴雨的重要原因;两个台风都具有低空急流、风速辐合、低层辐合高层辐散流场等有利于产生特大暴雨的环流形势特征;两个台风都存在低空偏东风和偏南风急流,两支急流为暴雨区提供了充足的水汽条件,低空急流较强的时段与强降水时段相对应;台风中心附近强辐合辐散区的建立和维持是产生特大暴雨重要的动力条件,水汽辐合区的面积和强度与暴雨区范围和降水强度相吻合;垂直速度大值区的维持时间与强降水的维持时间相一致;垂直速度、假相当位温和水汽通量散度的增大和减小,可作为降水增大和减弱的重要依据之一;暴雨区主要落在700 h Pa螺旋度场大值区内,所以螺旋度分析可为台风暴雨落区预报提供参考依据。     

“灿鸿”台风造成浙江东北部大暴雨成因分析

本文利用常规观测和自动站加密资料、卫星云图资料及NCEP再分析资料,分析了2015年7月10—11日1509号台风灿鸿造成其西侧浙江东北部异常强暴雨事件,得到本次大暴雨过程是由于"灿鸿"强度强、范围大、直接影响时间长,长时间东北气流下,在浙东北特殊地形作用下,形成地面辐合带造成的。台风影响前期该区域处在对流不稳定状态,水汽含量丰沛,低层辐合,高层辐散且气温低,有利于上升运动,上层水汽冷凝造成强降雨。暴雨区低层MPV1由负值转变为正值,导致垂直涡度加强,925 hPaθ_(se)的高能区的长期存在,有利于上升气流增强,水汽长时间大量输送有利于台风的发展和维持,也有利于强降雨的形成。这些物理量的变化与雨量增大和减小有6~12 h的提前。呈喇叭口状的杭州湾及南面四明山、狭长东北一西南走向的象山港以及南岸的山脉等地形有迎风坡作用和地形辐合,对东北气流参与造成的降雨有增幅作用。     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on