青藏高原一次冰雹强对流天气过程的诊断及雷达回波特征分析

利用青藏高原第三次科学实验的C波段双偏振雷达（C-POL）的观测资料、ERA-Interim 0.125°（纬度）×0.125°（经度）气象再分析资料、常规气象探空资料,对2014年7月30日午后发生在西藏那曲地区的冰雹强对流天气过程进行了天气诊断及雷达回波特征分析。结果表明:1）此次冰雹强对流过程发生在有切变线伴随的高原低涡东移过程中,低涡尾部前倾的切变线为这次冰雹的发生提供了动力、水汽条件。2）强对流天气的水汽输送主要来自从孟加拉湾、印度及尼泊尔翻越喜马拉雅山脉的水汽,强对流发生前水汽输送显著增加,低层水汽集中在400 hPa以下,有明显的辐合及垂直输送。3）那曲400 hPa以下为假相当位温随高度递减区,也是水平辐合及垂直上升运动的重合区,有明显的对流不稳定能量集聚及动力抬升条件。4）雷达回波图上可看到,此次强对流天气主要由局地新生的多个中γ尺度孤立对流单体造成,其移动路径与切变线前西南气流一致。大部分单体水平尺度不大,生命史短,但仍有部分单体强度大,生命史较长。局地气流辐合扰动会导致新的单体产生,单体的发生、发展及维持离不开低层气流辐合提供的动力条件。5）在距离高度显示图上表现出了弱单体雹云特征,雹云云顶伸展至16 km,高于夏季平原地区普遍对流云高度,但未突破对流层顶,0℃层远低于平原地区,为深厚强对流降水;强降水中心位于云团下部,即有降雹也有降水,降雹以霰粒为主;垂直方向存在强烈的入流和上升气流,悬挂回波出现在入流上升气流之上,中层辐合区的气流下沉区对应降雹区;中层辐合区与上层的高空辐散区配合导致对流风暴的垂直增长和强烈发展。     

基于多源探测资料的“4.12”非典型冰雹特征分析

针对2020年4月12日发生在江苏苏州的一次大范围雷暴大风、局部伴有冰雹的强对流天气过程,基于常州S波段双线偏振多普勒天气雷达、湖州和青浦的单偏振雷达以及再分析资料,详细分析了此次过程的天气背景,不稳定机制、抬升条件和雷达回波及双偏振雷达参量演变特征,并结合双雷达风场反演技术分析超级单体的动力结构及云物理机制。结果表明此次过程发生在高空冷涡南掉、横槽南摆,上下层强烈不稳定的环流背景下,地面有辐合线提供了触发条件。苏南地面附近至600 hPa为θ_se随高度减小的对流不稳定层和0~6 km强烈的垂直风向切变分别为此次过程提供强热力和动力不稳定条件。此次降雹天气过程,雷达回波强度超过50 dBZ,有明显的三体散射、气旋式辐合、高层回波悬垂和强风暴顶辐散等特征;但是VIL和ET都很小,呈现非典型冰雹特征。双线偏振雷达各偏振参量(差分反射率Z_DR、差分相移率K_DP和相关系数CC)也都反映出冰雹云的典型特征:在Z_H大、Z_DR小、CC小的区域出现冰雹,Z_DR值通常为-1.0~0.2 dB,CC值普遍小于0.85。上述双偏振参量特征在强对流短时临近预报和冰雹识别方面具有很强的应用潜力。利用双雷达风场反演技术对降雹时段研究,发现1~5 km各层高度的风垂直切变、辐合的存在,有利于超级单体的发展和加强。双雷达能较好地反演雷暴大风的三维风场精细结构,有助于加深对冰雹云结构的认识进而提高冰雹等强对流天气的预报预警能力。      

偏振雷达观测强对流雹暴云

根据偏振雷达原理,用C波段双线偏振天气雷达观测得到4例强对流雹暴演变过程的水平反射率ZH(dBZ)和差分反射率ZDR(dB)垂直剖面RHI定量回波资料,分析了这些雹云不同演变阶段的回波参量和偏振特性的关系,说明ZH、ZDR双参量对判别降雹有着明显优势,用雨滴谱的ZH-ZDR分布边界关系对这些雹云回波进行判别降雹分析,给出我国用偏振雷达观测和识别冰雹的研究结果。     

双偏振雷达在江苏“7.6”降雹过程中的应用分析

针对2019年7月6日发生在江苏徐州、宿迁、淮安、南京以及常州一线的一次大范围冰雹天气过程,利用再分析资料分析天气背景、不稳定机制和抬升条件。通过徐州和南京S波段双偏振雷达偏振参量及宿迁和淮安的双多普勒天气雷达风场反演技术对冰雹云的热动力结构和微物理特征开展了详细的分析。结果表明:此次大范围冰雹天气发生在高空冷涡南落、横槽南摆,低层暖湿气流北抬,上下层强烈不稳定的环流背景下,地面低压缓慢东移南压,提供了辐合抬升条件。此次降雹天气过程中,雷达回波图上显示有典型的冰雹云特征——三体散射长钉、回波穹隆结构、强度超过50 dBZ,中层径向辐合,风暴顶辐散等特征。双偏振雷达各偏振参量也表现出冰雹云的特点,出现冰雹的地区展现水平反射率因子ZH大、差分反射率因子ZDR小、相关系数CC小的特征,ZDR值为-1.0～0.5 dB,CC值小于0.85;超级单体在近地层还出现表征入流区的CC谷、ZDR柱、差分相移率KDP柱等特征。ZDR柱、KDP柱和CC谷等双偏振参量特征在强对流短时临近预报和冰雹识别方面具有很强的应用潜力。双雷达风场反演表明此次过程降雹集中时段,冰雹云的穹隆空间结构,降雹时刻存在的明显下沉气流。     

一次长生命史超级单体风暴的雷达观测特征

利用地面观测资料、探空资料以及石家庄多普勒天气雷达和饶阳双偏振雷达资料等,对2018年6月13日影响河北中南地区的一个长生命史超级单体风暴的环流背景、雷达观测特征等进行了分析。结果表明:(1)此超级单体发生在涡后横槽转竖的环流背景下。(2)风暴生命史长204 min,其中超级单体维持时间长达138 min,其间雷达最大反射率因子基本上维持在65 dBz以上。(3)中气旋深厚并强烈发展是超级单体发展和维持的重要动力机制。中气旋底高最低可达风暴底部,顶高变化幅度较小,低质心中气旋和高质心中气旋的形成和发展都可能引起地面降雹,降雹期间对应超级单体短暂减弱。(4)超级单体维持期间一直伴有气旋、反气旋涡旋对特征。超级单体的钩状回波特征明显,表现为典型的回波墙-弱回波区-悬挂回波的垂直结构;低层辐合、高层辐散,高空辐散大于低层辐合,有利于超级单体内部强烈的旋转上升运动;有明显的三体散射和旁瓣回波,三体散射最长超过60 km,持续时间长达150 min。(5)双偏振雷达探测的超级单体反射率因子≥55 dBz,对应位置差分反射率-0.5~0.5 dB,差分传播相移率仅1.5~2.0°/km,相关系数在0.75~0.92之间,表明超级单体内同时存在液滴和较大冰雹。     

2006年6月28日河南省强对流天气过程分析

利用濮阳、三门峡新一代天气雷达产品及云图、自动站等资料,分析了2006年6月28日河南省强对流天气过程.结果表明:濮阳新一代天气雷达基本反射率明显特征为弓形带状回波,对应径向速度上为一条明显的辐合线,强降水回波带和此中尺度辐合线位置吻合;三门峡新一代天气雷达显示,洛宁冰雹的组合反射率达65dBz,回波顶高达14～17 km,垂直液态含水量达55～65 kg·m-2,径向速度产品显示有中尺度气旋,以上特征早于降雹30 min左右出现.     

清远地区“2019·02·20”降雹天气过程特征分析

基于清远连州双偏振雷达探测资料、清远探空资料和地面观测资料,对2019年2月20日陆续发生在阳山、连山、连南、连州的冰雹天气过程天气背景、雷达回波和双偏振特征进行了分析。结果表明:风暴发生在南支槽加深东移,西南低空急流发展和低层切变线南压的大尺度环流背景下,锋面低槽触发使其对流发生。“上干下湿”的典型大气层结结构、适宜的高度(0℃层高度在3.7~4.2km、-20℃层高度在6.8~7.1km)、低层的弱逆温层,均有利于能量聚集迸发。在回波强度大于50dBz区域中,有明显的三体散射、气旋式辐合、回波悬垂和有界弱回波区等特征;其中阳山降雹单体VIL值随时间的变化趋势与风暴强度的变化趋势成正比,且具有水平反射率因子高、差分反射率低(-1~0.5dB),相关系数较低(0.8~0.94)的典型双偏振特征。     

不同波段雷达在咸阳冰雹过程中的应用分析

利用常规气象观测资料、探空资料、NCEP/NCAR 1°×1°网格点逐6 h再分析资料、西安C波段新一代天气雷达和旬邑X波段双偏振天气雷达资料,对2018年6月13日发生在咸阳北部的一次冰雹天气进行雷达回波特征和成因分析。结果表明,该次冰雹发生在高层冷空气下滑、中低层存在辐合上升运动的环境背景下,降雹出现在冷涡底后部,较强对流不稳定能量、较好的热力不稳定条件和一定的垂直风切变为冰雹的发生提供了有利条件。西安C波段雷达和旬邑X波段雷达的反射率因子均表现出冰雹的弱回波区和三体散射特征,但两部雷达的回波特征有所差别：在同一高度上旬邑X波段雷达的回波强度比西安C波段雷达的弱;VIL的骤增、差分反射率因子ZDR、差分传播相移因子KDP、零延迟相关系数RHV等偏振参量对冰雹的指示性也较好,当VIL最大值达到40 kg/m2、密度高于3.5 g/m3,ZDR为0或负值,RHV迅速降低,KDP接近于0,可判定冰雹生成。     

浙江省２月份连续降雹过程诊断

利用NCEP再分析资料、MICAPS常规资料、雷达产品等资料对浙江省2009年2月23—26日连续降雹天气过程进行了诊断分析。结果表明:此次连续降雹过程降雹区均出现在高低空急流轴交叉点南侧约1个纬度,底层辐合区;850 hPa较强的水汽辐合和湿舌为此次降对流过程提供了充沛的水汽条件,上干下湿结构使对流性不稳定增强,逆温层存在使大量不稳定能量储积起来,底层冷空气渗透触发强对流发生;Ic500-700指数对此次降雹过程有较好指示意义;2月份冰雹雷达回波特征有别于春、夏季冰雹回波特征,冬末春初冷空气势力仍较强,对流强度偏弱,回波顶高偏低,其三体散射特征不明显,VIL值较小。     

2006年6月28日河南省强对流天气过程分析

利用濮阳、三门峡新一代天气雷达产品及云图、自动站等资料,分析了2006年6月28日河南省强对流天气过程。结果表明:濮阳新一代天气雷达基本反射率明显特征为弓形带状回波,对应径向速度上为一条明显的辐合线,强降水回波带和此中尺度辐合线位置吻合;三门峡新一代天气雷达显示,洛宁冰雹的组合反射率达65dB z,回波顶高达14~17 km,垂直液态含水量达55~65 kg.m-2,径向速度产品显示有中尺度气旋,以上特征早于降雹30 m in左右出现。     

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.     

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.     

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.     

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