四川盆地一次极端大风天气过程成因及预报着眼点分析

利用常规观测资料、FY-2E卫星云图、多普勒雷达产品、闪电定位资料、自动气象站资料等,分析了2015年4月4日傍晚到夜间发生在四川盆地的极端大风天气过程。分析指出:本次雷暴大风过程是由冷锋对暖湿气团的强迫抬升及干冷空气进入暖湿区域触发形成.中空干层、大的温度直减率、高低空急流耦合区、低层温度脊附近是利于极端雷暴大风出现的潜势区域。该区域为雷暴形成提供了条件不稳定、水汽、动力抬升等有利环境条件。冷空气首先从盆地西北部中低层入侵,在低层切变线上触发生成了一系列雷暴单体,在最有利于对流发展的潜势区域迅速发展。潜势区域中线状回波北段的中尺度涡旋环流、前侧入流和后侧入流的相互作用形成单体弓形回波,该弓形回波具有比普通雷暴更高的反射率因子、垂直液态含水量.根据雷达回波演变特征推断,本次极端大风是由单体弓形回波带来的湿下击暴流所导致。弓形回波中高反射率因子的高度连续下降意味着下沉气流伴随降水粒子下降,干空气被夹卷进入下沉气流使得雨滴被迅速蒸发,大大加强了下沉气流强度,因而显著增加了大风强度。分析还指出:通过分析对流发展背景条件,确定最有利对流发展的潜势区域,关注该区域中回波的生成、形态特点、演变特征,可提前预警大风天气。     

S波段双偏振多普勒天气雷达对一次局地强雷暴过程的探测分析

为提高双偏振天气雷达雷暴监测预警能力,探究雷暴活动过程雷达偏振信息特征及雷暴内部微物理过程,利用S波段双偏振多普勒天气雷达,结合地面大气电场仪和闪电定位系统资料对2015年8月31日发生在南京地区一次局地强雷暴过程进行了分析。主要利用体扫数据获得雷暴单体内部垂直剖面(Vertical Cross Section,VCS),同时结合模糊逻辑算法进行粒子类型识别,得到多个偏振参量和雷暴云内部粒子类型的垂直分布情况,进一步分析得到各偏振参量和粒子分布随闪电活动的演变规律。结果表明:在-15℃高度层以上冰晶区域出现K_(DP)的负值区与闪电活动具有很好的相关性;雷暴云中霰粒子的分布变化同闪电活动演变同步很好,在一定高度霰粒子的出现可以用来对雷暴进行预警;雷暴云中低层存在强烈的辐合上升区,利于霰和冰晶碰撞非感应起电和闪电的发生。     

一次夏季雷暴天气过程中闪电活动特征分析

利用探空资料、多普勒天气雷达和闪电定位仪数据,分析了2009年7月30日发生在南京地区一次雷暴天气过程的雷达及闪电数据时空演变特征。结果表明：对流有效位能Ecap比起K指数（IK）等对于对流潜势预报具有更明显的指示作用,0 ℃层和-10 ℃层高度的降低有利于雷暴云的雷电活动;整个过程以负闪为主导,闪电强度越大,闪电频数也越高,每次闪电峰值后,都对应一次谷值;闪电数据与多普勒天气雷达回波叠加后分析发现,回波的生消演变对应着闪电频数和强度的生消演变,负闪主要落在强回波中心区域,正闪零星分布于回波强度梯度较大的区域;雷达径向速度图像特征变化更能揭示闪电发生发展的机制,逆风区对应雷暴中心区域,不仅是强降水的中心区也是闪电的中心区,对逆风区的识别监测能够更好的指导雷暴预警报工作;利用雷达数据计算的云底动能施力参量,能够很好的描述支持闪电起电的热动力特征,云底动能施力对雷电增长的贡献有一段持续传输过程,该参量峰值比频闪峰值和强度峰值都约有0.5 h的提前量。     

南京地区一次冬季雷暴过程的雷达回波特征分析

为研究雷暴发展过程中的雷达回波特征,利用S波段双偏振多普勒天气雷达对南京地区的雷暴进行了观测研究,利用雷达回波资料、地面大气电场数据、闪电定位数据及探空资料对比分析了2014年一次冬季雷暴过程与夏季雷暴的雷暴回波特征差异。分析结果表明:冬季雷暴的对流发展高度明显低于夏季雷暴,持续时间短,水平尺度小,有较大比例的正闪;影响冬季雷暴与夏季雷暴的成雷对流高度差异的主要因素是环境温度差异,冬季雷暴在较低的高度上,具有较低的环境温度,更有利于雷暴起电;对流单体中,霰粒子的存在是雷暴的一项重要特征。     

基于X波段双偏振雷达对雷暴单体中水成物粒子演变特征的研究

为了解雷暴单体内部水成物粒子分布结构及演变过程,综合X波段双线偏振天气雷达的参量及环境温度参数,结合小波去噪和自适应约束算法进行资料预处理后,基于模糊逻辑算法对北京一个结构演变相对完整的典型雷暴单体内水成物粒子分布随时间演变特征进行系统的分析,得到如下结果:（1）按雷暴单体的宏观特征将其演变过程分为发展、成熟和消散阶段。三个阶段中单体平均高度分别为11、12、10 km;回波强度最大可达40~45 dBZ、大于50 dBZ和40~45 dBZ;霰粒子占各自阶段单体内所有粒子百分比分别为2%、12%和1%。（2）各阶段主要微物理过程及演变特征是:发展阶段,单体0℃层以下由暖云过程主导,毛毛雨占5%,雨滴占24%;少量液态粒子上升至0℃层以上与冰晶反应生成1%干霰,冷云过程较弱。成熟阶段,相较发展阶段0℃层以下毛毛雨减少约2个百分点,雨滴增多约2个百分点,粒子碰并加强,暖云过程增强;较多液态粒子上升至0℃层以上,约有4%的雨滴与5%的冰晶通过凇附作用生成7%的霰,冷云过程增强。消散阶段,下层液态粒子难以上升至0℃层以上形成初始冰晶,使暖云及冷云过程都减弱,0℃层以下毛毛雨相较成熟阶段平均增多约1个百分点,粒子碰并减弱;0℃层以上冰晶消耗减少2个百分点,霰生成减少5个百分点。（3）基于雷暴单体内各类水成物粒子分布、演变及其动力场背景特征建立了雷暴单体演变过程微物理模型。本文研究有助于加深对典型雷暴单体内部水成物粒子分布和微物理过程的认识,可以为雷暴天气的预警和预报提供必要的指导。     

基于温度层强回波区域面积的天气雷达雷暴自动识别方法北大核心

为利用天气雷达回波资料实现雷暴的自动识别,提出了一种基于温度层强回波区域面积的天气雷达雷暴自动识别方法。该方法首先利用雷达回波体扫数据在水平范围内搜索强回波区域;再对某一温度层上,达到设定阈值的雷达回波反射率因子的区域进行面积求和,当水平范围强回波区域面积达到识别面积阈值时,判定该强回波区域为雷暴区域。在此基础上,结合S波段双偏振多普勒天气雷达观测资料、闪电定位资料,采用了17个雷暴天气过程的312个雷暴区域检验识别算法。结果表明:当等高度平面位置显示(CAPPI)数据处理中采用(35 dBZ,0℃,2 km^(2))参数组合能够达到最优的识别效果,识别概率可达87.5%,虚警率为32.9%,临界成功指数为61.2%。该方法可以用于天气雷达的雷暴计算机自动识别业务。     

吉林地区一次雷暴云个例电和云微物理特征的模拟分析

利用三维强风暴动力一电藕合数值模式, 结合闪电定位仪资料、雷达回波资料及降水资料,分析了吉林地区一次雷暴云个例在发生第一次闪电前云内电场的发展情况及微物理变化过程,并与青藏高原一次典型雷暴过程进行了对比.结果表明:云发展成熟时,云中呈现上正下负及云下部次正的三极性分布,主负电荷区稳定在-10℃层附近,次正电荷区浓度较大;上升气流穿过-15℃层之上开始强起电;云中最大电场出现在上升速度达到最大值后回落的阶段;闪电频数与云发展的高度及回波强度有关,回波强度＞45 dBz时,云发展越高,闪电频数越大,云顶高度＜6 km时,闪电发生较少;青藏高原雷暴具有与我国北方雷暴明显不同的特征.     

北京地区雷暴的雷达回波特征与闪电活动的相关关系

基于雷达资料以及SFAIR 3000闪电定位资料分析了北京地区14次雷暴过程,研究了闪电活动与雷暴的雷达回波反射率体积的相关性。结果表明：反射率体积与总闪频次有着较好的相关性,其中-15℃层以上超过30 dBz的反射率体积与总闪频次的相关系数为0.89,其指数拟合优度为0.83。北京地区雷暴的单个闪电表征回波体积（VPF）在闪电活动开始时期有较高的水平,但在闪电活动结束时期较小。VPF还可作为闪电活动消亡的指示因子。     

基于卫星资料的大连地区强对流天气闪电活动特征

利用FY-4卫星云顶亮温（Cloud Top Temperature,CTT）资料和雷达回波资料,分析了2019年6-9月大连地区的闪电活动特征,重点分析了该地区2019年9月4日的一次强对流天气闪电活动特征与雷达回波及CTT之间的相关性。结果表明：此次过程雷暴起始于大连东南方向。在雷暴初始阶段,以云闪为主,云闪高度主要集中在7-12 km。闪电活动主要集中在雷达回波强度>30 dBz的区域,对应的云顶高度超过了8 km。闪电活动与FY-4卫星CTT之间存在较好的相关性,闪电主要发生在CTT为240-250 K左右区域。对2019年5-8月大连地区雷达与闪电活动进行量化分析,发现闪电活动主要集中于雷达组合反射率39.38 dBz附近区域,对应的云顶高度为8.21 km。     

平凉一次雷暴云内的降水粒子分布及其电学特征的探讨

利用X波段多普勒双偏振雷达在甘肃平凉地区获取的一次雷暴过程资料,采用模糊逻辑判断法详细分析了该过程云内降水粒子的时空演变特征,同时结合该地区雷暴的电学特征,探讨了雷暴云电荷结构与云内降水粒子之间的关系。结果表明,在雷暴发展的不同阶段,各种降水粒子的数量存在较大的差异,霰粒子和干雪的演变特征与雷暴的发展、成熟到减弱过程对应比较一致。结合地面电场和雷达推断,冰相粒子特别是霰粒子和冰晶粒子与雷暴云的起电存在密切的关系。从各种粒子的垂直分布特征来看,中国内陆高原雷暴云下部正电荷区的强弱最有可能由霰粒子的多少来决定;同时利用霰粒-冰晶起电机制可以较好地解释雷暴云内三极性电荷结构的形成。     

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.     

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     

全球贸易隐含碳变化及其影响分析

基于最新的GTAP8 (Global Trade Analysis Project）数据库,使用投入产出法,分析了2004年到2007年全球贸易变化下南北集团贸易隐含碳变化及对全球碳排放的影响。结果显示,随着发展中国家进出口规模扩张,全球贸易隐含碳流向的重心逐渐向发展中国家转移。2004年到2007年,发达国家高端设备制造业和服务业出口以及发展中国家资源、能源密集型行业及中低端制造业出口的趋势加强,该过程的生产转移导致全球碳排放增长4.15亿t,占研究时段全球贸易隐含碳增量的63%。未来发展中国家的出口隐含碳比重还将进一步提高。贸易变化带来的南北集团隐含碳流动变化对全球应对气候变化行动的影响日益突出,发达国家对此负有重要责任。     

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.     

Retrieval of outgoing longwave radiation from COMS narrowband infrared imagery

Hourly outgoing longwave radiation(OLR) from the geostationary satellite Communication Oceanography Meteorological Satellite(COMS) has been retrieved since June 2010. The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels. This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm(OLR12.0using the 12.0 μm channel) and three multiple-channel algorithms(OLR10.8+12.0using the 10.8 and 12.0 μm channels; OLR6.7+10.8using the 6.7 and 10.8 μm channels; and OLR All using the 6.7, 10.8, and 12.0 μm channels). The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth's Radiant Energy System(CERES) over the full COMS field of view [roughly(50°S–50°N, 70°–170°E)] during April 2011.Validation results show that the root-mean-square errors of COMS OLRs are 5–7 W m-2, which indicates good agreement with CERES OLR over the vast domain. OLR6.7+10.8and OLR All have much smaller errors(～ 6 W m-2) than OLR12.0and OLR10.8+12.0(～ 8 W m-2). Moreover, the small errors of OLR6.7+10.8and OLR All are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration. These results indicate a noteworthy role of the6.7 μm water vapor absorption channel in improving the accuracy of the OLRs. The dependence of the accuracy of COMS OLRs on various surface, atmospheric, and observational conditions is also discussed.