“14·02”湖南三次雨雪过程对比分析

本文利用常规探空和地面观测资料、NCEP 1.0×1.0再分析资料及多普勒雷达资料,对2014年2月上中旬发生在湖南的三次雨雪过程(简称"14·02")进行了对比分析。结果表明:(1)第一次过程湘南出现冻雨,温度层结表现为850~700 hPa有明显逆温层,700 hPa温度高于0℃,850和925 hPa温度低于-4℃,地面温度低于0℃。从主要影响系统配置来看,700 hPa强盛的西南急流为水汽的输送和湘南融化层的形成和维持起到了重要作用,低层冷空气受南岭山脉阻挡而形成的地面静止锋和深厚的冷垫是导致湘南冻雨较长时间维持的原因。(2)第二、三次过程以降雪为主,温度层结显示地面温度0℃左右,地面以上层次温度低于0℃。(3)第三次雨雪强度最强,暖湿空气沿锋面强迫抬升,在低层冷空气共同作用下,导致较强雨雪天气的发生。雷达回波显示强降雪过程具有积层混合性降水回波及低质心高效降水回波特征。     

2008年初持续雨雪灾害过程分析

利用地面实况资料与长沙单站探空等观测资料,对2008年1月中下旬至2月上旬初发生在湖南的低温、雨雪、冻雨灾害天气过程的影响实况和成因进行了分析.结果表明:中高纬阻高的建立、崩溃、重建导致其前部的鄂霍茨克海低涡不断引导冷空气南下,是产生低温、雨雪、冻雨的大气环流背景;南支锋区上强盛的西南气流带来了充沛的水汽,与北支锋区上南下的冷空气结合时,出现了持续的冻雨,当冻雨形成后逆温的强弱、融化层厚度及暖层温度高低、冷却层厚度、700 hPa西南气流强弱、日平均气温与日雨量的变化都与冻雨厚度变化密切相关;当高空南支有低槽分裂东移,中低层西南大风核上强烈的水汽辐合与阻高崩溃横槽转竖带来的冷空气共同作用影响时,为南方大范围暴雪过程提供了动力、水汽和凝结条件.     

2018年广西一次极端低温雨雪冰冻灾害成因分析

利用NCEP和FNL再分析资料及地面气象观测站气温等观测资料,对2018年12月28日至31日广西发生的一次极端低温雨雪冰冻事件进行天气形势分析.结果 表明,乌拉尔山阻塞高压强而稳定,贝加尔湖附近500hPa气温有-52℃的冷中心,同时与横槽配合,是地面冷空气中心堆积加强的原因;副热带高压的异常偏强,造成广西南北温差较大;中纬度锋区强盛,850hPa南北温度梯度达22℃,提供了热力和动力条件;中低层锋区的结构造成了广西北部和中部、南部降水相态的明显区别;持续且深厚的水汽输送为这次低温雨雪冰冻过程提供有利的水汽条件.     

一次大暴雨天气的多普勒雷达回波分析

通过对2008年5月3日发生在驻马店市正阳县的大暴雨过程中的环流形势、稳定度及多普勒雷达产品的分析发现:驻马店地区K指数=38 ℃、SI=-2.0 ℃、Δθse=3.8 ℃,大气层结极不稳定,为大暴雨的产生提供了充足的不稳定能量;500 hPa低槽和700、850 hPa切变线及地面冷空气入侵,触发了不稳定能量的释放,产生了大暴雨.利用多普勒雷达回波产品,可确定雨区及其移动方向;利用径向速度资料,可确定辐合带;利用风廓线资料,可确定温度平流、垂直风切变及冷空气入侵.     

2018年9月丹东连续两次风雹天气的多尺度对比分析

利用高空、地面等常规气象资料和多普勒雷达等气象观测资料,以及NCEP再分析资料,对丹东2018年9月连续出现的两次风雹天气进行对比分析,探讨和总结两次风雹天气过程形成、维持、发展成因的异同。结果表明：中低层切变线、强垂直风切变和辐合抬升有利于风雹天气的发生。高空冷空气的入侵方式和强度、低空急流建立、环境垂直风切变强度对风雹天气剧烈程度有重要影响。两次风雹天气过程分别为东北冷涡型和高空冷槽型,9月6日横槽转竖引导冷空气快速移动并且后方还有冷涡后部的冷空气不断补充,配合850 hPa西南急流带来充沛水汽,使得6日风雹天气现象较3日更加剧烈;两次风雹天气过程在多普勒雷达回波上的特征明显。9月3日的风雹过程由多单体线对流风暴在东移过程中逐渐演变成弓形回波,在径向速度图上有明显的逆风区;9月6日的风雹过程沿地面辐合线激发多个超级单体呈现列车效应移动,径向速度图上出现了速度模糊,有较高的垂直累积液态水含量（Vertical Integrated Liquid water content,VIL）。     

2008年华南西部罕见低温冷害天气成因分析

利用ECMWF和Micaps提供的常规观测资料,对2008年1月华南西部遭遇50年罕见的低温雨雪冰冻极端天气事件过程进行分析。结果表明：蒙古横槽南压分裂小槽东移,使地面冷高压强度突然增强并爆发南下,是造成华南西部寒潮天气的起因;北半球中高纬度出现双阻型高压(乌拉尔山阻高和阿留申群岛阻高),使大气环流形势异常稳定,是导致低温雨雪冰冻天气持续性的直接原因;低纬度南支低压槽活跃,西南暖湿空气不断向我国南方输送,华南西部低空相对湿度大,水汽辐合条件及上升运动都对阴雨天气的维持有利;在850 hPa华南上空形成一支稳定的强锋区,大气层出现近地面冷、中层暖、高层冷的结构,加剧了雨雪冻雨的形成。     

2008年初江西低温雨雪冰冻天气过程成因探讨

利用T213资料以及常规观测资料,对2008年初江西省持续性低温雨雪冰冻天气过程进行了分析。结果表明,乌拉尔山高压脊稳定维持,副高持续偏北、偏强,地面冷空气不断南下,850hPa层气温始终维持在0℃以下,是造成江西2008年低温雨雪冰冻天气的直接原因。副高和乌拉尔山高压的强度均在不断增强,控制范围不断扩大,导致江西出现三种性质截然不同的降水。700hPa层气温的变化与江西降水性质关系密切,气温为0℃以上时,水汽呈液相态,主要为雨或雨夹雪天气;气温为0℃以下时,水汽呈固相态,以降雪天气为主。中层和低层的水汽输送均可产生冻雨和大雪天气,江西1月25-26日冻雨天气的水汽主要来源于低层输送,28日晚-29日大雪天气的水汽来源于中层和低层的输送,31日晚-2月2日大雪天气的水汽则来源于中层的输送。     

2013年初桂北寒潮天气过程分析

运用Micaps资料和地面观测实况资料,对2013年1月3-5日桂北寒潮天气过程进行了诊断分析,结果表明：（1）此次寒潮天气过程的特点是降温快、回温慢,且过程日平均气温低;（2）此次寒潮过程的冷空气堆积过程完成后,是由横槽转竖引导槽后冷空气大举南下入侵广西,造成的桂北寒潮天气;（3）中暖下冷的逆温层结维持时间与降雪冻雨时段对应较好,逆温层结被破坏后,桂北的持续雨雪天气也宣告结束,气温开始逐步回升;（4）中低层水汽辐合及较强的槽前正涡度平流也是产生降雪的必要条件之一。     

2016年广东一次罕见寒潮雨雪冰冻天气过程分析

利用常规气象观测资料、NCEP/NCAR再分析资料,分析了2016年1月下旬广东罕见大范围雨雪冰冻天气过程的大尺度环流和冷空气活动特征、动力和水汽条件,采用湿球温度讨论了降水相态和大气温度垂直结构特征。结果表明：此次寒潮过程环流形势为横槽转竖型,横槽下摆引导强冷空气向南迅猛爆发,以及伴随着异常强的冷高压、锋区、冷温度中心和冷温度平流的冷空气主力南侵,是本次寒潮过程粤北和广东中南部温度陡降的主要原因;700 hPa冷暖空气的辐合,以及700 hPa西南气流从孟加拉湾输送水汽经中南半岛北部到北部湾至华南地区加强并辐合,是造成雨雪冰冻天气产生的重要动力和水汽条件;在有利的大尺度环流、动力和水汽条件配合下,降水相态的变化与暖层强度及湿球温度密切相关,暖层的明显减弱及暖层下方湿球温度低于0 ℃冷冻层的强度增强,导致降水相态由雨向雪、雨夹雪、霰等固态降水转变;在发生固态降水的平均时段内,粤北地区中低层湿球温度均低于0 ℃,无明显融化作用,产生纯雪或雨夹雪的可能性大;而位置偏南的珠江三角洲地区仍存在浅薄的暖层,因此主要出现雨夹雪或霰。当寒潮入侵涉及华南降水相态预报时,需要注重实况探空和模式预报探空的大气温湿垂直结构的分析,更应重视湿球温度的研究和应用。     

2008年湖南极端冰冻特大灾害天气成因分析

2008年初,湖南出现了有完整气象记录以来罕见的特大低温冰冻雨雪极端灾害天气.常规资料分析表明,高空中高纬阻塞高压稳定,副高持续偏强,孟加拉湾低槽稳定少动,湖南一直处于槽前西南气温中;700hPa西南急流带来大量暖湿气流,一方面有利于降水的形成与持续,另一方面有利于逆温层的形成;850hPa切变线在湖南境内南北摆动,造成全省大范围降水;地面冷空气不断从洞庭湖区补充南下.大环流背景有利于低温冰冻天气的维持.分析探空站的大气层结、地面气象要素与冰冻的关系表明:大气层结的逆温层、融化层,地面温度在0℃附近及以下是形成冰冻的关键因子;降水对于冰冻的形成具有重要作用,日降水量大于0.1mm持续性大范围稳定性的雨夹雪或小雨有利于冰冻的形成与加强;气温与冰冻的发展呈反相关;当大气层结、降水量与海拔高度基本相同时,气温是冰冻发展的关键因子.     

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.     

VARIABILITY OF INTER-ANNUAL RELATIONSHIP BETWEEN INDIAN OCEAN DIPOLE AND HUAXI REGION’S AUTUMN PRECIPITATION

The moving-window correlation analysis was applied to investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the synchronous autumn precipitation in Huaxi region, based on the daily precipitation, sea surface temperature (SST) and atmospheric circulation data from 1960 to 2012. The correlation curves of IOD and the early modulation of Huaxi region’s autumn precipitation indicated a mutational site appeared in the 1970s. During 1960 to 1979, when the IOD was in positive phase in autumn, the circulations changed from a “W” shape to an ”M” shape at 500 hPa in Asia middle-high latitude region. Cold flux got into the Sichuan province with Northwest flow, the positive anomaly of the water vapor flux transported from Western Pacific to Huaxi region strengthened, caused precipitation increase in east Huaxi region. During 1980 to 1999, when the IOD in autumn was positive phase, the atmospheric circulation presented a “W” shape at 500 hPa, the positive anomaly of the water vapor flux transported from Bay of Bengal to Huaxi region strengthened, caused precipitation ascend in west Huaxi region. In summary, the Indian Ocean changed from cold phase to warm phase since the 1970s, caused the instability of the inter-annual relationship between the IOD and the autumn rainfall in Huaxi region.     

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