新疆雷暴的统计特征

2017年6月7日阿克苏地区出现一次强对流天气过程,其中2个α中尺度对流系统（MCS）及其合并发展造成多站大风、冰雹和短时强降水。为探明该过程地闪分布及其与云顶亮温（TBB）、雷达回波和对流系统发展的关系,加深对新疆强对流天气中地闪活动规律和特征的认识,利用新疆地闪监测定位系统数据、卫星TBB资料、C波段多普勒天气雷达资料等,分析了此次强对流天气过程地闪活动特征。结果表明：（1）对流层低层和中层明显增湿,低空中尺度切变线稳定维持,使得地闪集中分布在低空切变线暖平流一侧。（2）该过程以负地闪活动为主,地闪强度由西向东呈增强趋势,地闪强度与地闪密度分布存在一定的负相关,地闪次数跃增和正地闪占比下降与地面大范围强风有着较好的相关性。（3）地闪多发生在TBB≤-40℃云区内,地闪次数与TBB≤-40℃云团面积和最低TBB分别呈正相关和负相关。（4）MCS影响期间负地闪和正地闪多发生在5~20 dBz和10~15 dBz回波区内;对流发生发展和成熟阶段垂直积分液态水含量（VIL）峰值较地闪次数剧增提前12~20 min出现。地闪次数与回波顶高对流发生发展阶段呈正相关关系,成熟阶段呈负相关关系。

     

Evolutionary characteristics of a dust storm over Oman on 2 February 2008

The evolutionary characteristics of a dust storm over Oman on 2 February 2008 were studied by analyzing the weather associated with it. The National Center for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis wind flow pattern at 1,000?hPa showed a clockwise and outward wind flow pattern over the study region, a manifestation of a high-pressure cold air mass. In addition, ground truth observations for surface temperature and surface winds showed cold northerly winds until the early morning of 2 February 2008. A strong wind shear resulted from differences in wind speed between warm air and trapped cold air. This vertical wind shear enhanced instability. Furthermore, the weakening of the inversion in the lower troposphere and the formation of a mixed layer due to transfer of horizontal momentum from upper air towards the surface led to strong surface winds. These strong winds lifted a large amount of dust particles off the ground, resulting in the dust event of 2 February 2008.     

“4.12“强沙尘暴天气中期分析

从中期预报的角度,对2000年4月12日甘肃河西中东部强沙尘暴天气过程的环流演变特征、波谱特征以及冷空气活动等方面,进行了初步分析.分析结果表明,这次强沙尘暴天气是在2波转1波的环流调整中生成长波槽,其后又在1波转2波,3波增幅的情况下,由长波槽调整造成的.     

Lightning activity related to satellite and radar observations of a mesoscale convective system over Texas on 7–8 April 2002

A multi-sensor study of the leading-line, trailing-stratiform (LLTS) mesoscale convective system (MCS) that developed over Texas in the afternoon of 7 April 2002 is presented. The analysis relies mainly on operationally available data sources such as GOES East satellite imagery, WSR-88D radar data and NLDN cloud-to-ground flash data. In addition, total lightning information in three dimensions from the LDAR II network in the Dallas–Ft. Worth region is used.GOES East satellite imagery revealed several ring-like cloud top structures with a diameter of about 100 km during MCS formation. The Throckmorton tornadic supercell, which had formed just ahead of the developing linear MCS, was characterized by a high CG+ percentage below a V-shaped cloud top overshoot north of the tornado swath. There were indications of the presence of a tilted electrical dipole in this storm. Also this supercell had low average CG− first stroke currents and flash multiplicities. Interestingly, especially the average CG+ flash multiplicity in the Throckmorton storm showed oscillations with an estimated period of about 15 min.Later on, in the mature LLTS MCS, the radar versus lightning activity comparison revealed two dominant discharge regions at the back of the convective leading edge and a gentle descent of the upper intracloud lightning region into the trailing stratiform region, apparently coupled to hydrometeor sedimentation. There was evidence for an inverted dipole in the stratiform region of the LLTS MCS, and CG+ flashes from the stratiform region had high first return stroke peak currents.     

“4.12“强沙尘暴中小尺度天气分析

利用地面气压场,有关气象站的气压、气温、湿度、风速自记资料,对2000年4月12日天气过程进行了分析和研究.分析结果表明,这次强沙尘暴的触发系统主要是冷锋过境,而中小尺度系统扰动则起到了激发和加强作用.     

2013年4月29日皖西南强风暴天气雷达资料分析

2013 年4 月29 日下午皖西南的安庆市和东至县发生了一次冰雹、雷雨大风强天气过程。本文以九江雷达资料为主,辅以GFS 预报场和地面资料,重点对风暴单体雷达特征、雷达物理量参数演变规律进行了分析。结果表明：(1) 雷达反射率因子图上,强风暴单体为涡旋状回波,回波前沿存在反射率因子高梯度区;速度图上涡旋状回波区对应着连续出现中气旋的现象,说明强风暴单体为具有涡旋形态的超级单体;强风暴顶高于11 km,大于50 dBz 的强反射率因子高度超过-20 C 层的高度等特征是产生大冰雹的重要指标。(2) 风暴和中气旋参数分析表明,冰雹发生在最大反射率因子高度(HT)和风暴顶高(TOP)出现最强值的上升阶段中,最大垂直液态水含量(VIL)为58 kg·m-2,最大反射率因子(DBZM)极值为77 dBz;VIL 密度（DVIL）≥4.0 g·m-3的持续时间达1 h 以上,其最大值超过6.0 g·m-3。(3) 该过程大冰雹产生在最大DVIL值出现后半小时,在DVIL为5.0 g·m-3时且在高梯度区附近出现;大风出现在中气旋持续时间较长和中气旋位置较高的时候。     

A decadal abruption of midwinter storm tracks over North Pacific from 1951 to 2010

风暴轴作为中纬度天气尺度瞬变涡动最强烈的区域,在中纬度天气和气候系统中扮演着至关重要的角色。本文通过Butterworth带通滤波、EOF分析及合成分析等气象统计方法,探究了1951–2010年北太平洋深冬(1月份)风暴轴的年代际变化及可能影响机制。根据Mann-Kendall突变检验结果,风暴轴在1982/1983左右有明显的年代际突变,突变前后EOF分布基本类似。P1时期(1955–1982年),热带西太平洋强烈且持续的ENSO信号通过西风急流来影响风暴轴,即在厄尔尼诺年间,风暴轴中心强度明显增强且向赤道方向移动,拉尼娜年恰好相反。P2时期(1983–2010年),位于风暴轴入口处的中纬度海洋锋区,由于其南北两侧感热通量的不同,引起局地近地层斜压增长,风暴轴强度增强。     

A warm season climatology of mesoscale convective systems in the Mediterranean basin using satellite data

A 3-year climatology of isolated warm season mesoscale convective systems (MCSs) was built for the Mediterranean basin using Meteosat Second Generation infrared imagery and an objective identification and tracking algorithm. A dataset of 4,718 MCS trajectories was constructed for the warm season of the period 2005–2007, which in turn was split into two subsets (deep and weak convective) according to the intensity of convection using a discriminant parameter in the MCS properties. Several parameters related to geographical, temporal, radiative, morphological, and motion related properties were calculated for each MCS. The majority of MCSs are mainly continental and strongly correlated with orography showing an increased formation from April to June when maximum is found. Initiation and dissipation time revealed a distinct diurnal cycle having a strong correlation with the typical diurnal heating cycle of the atmosphere. On average, a typical isolated MCS in the Mediterranean basin initiates between 14:00 and 17:00 local solar time, tends to be small with elongated shape, short-lived, usually moving toward northeast to southeast with a mean velocity of 36 km/h. When comparing the two MCS subsets, some notable differences were revealed. Weak convective MCSs initiate earlier, move faster, travel longer, tend to reach slightly smaller sizes, are more linear, present higher cloud top temperatures, and have lower fractions of convective cloud type areas than deep convective systems.     

基于FY-2D的新疆强对流云的识别

利用2007-2013年新疆的十场强对流天气过程以及与之相应的FY-2D静止气象卫星数据,分析了强对流云红外一通道、红外二通道、水汽通道及通道差的光谱特征,提取强对流云团样本点,采用统计方法确定判识指标的阈值范围,构建多通道多阈值判识方法。利用三场天气过程的地面实测降水资料分别验证了单时次和整场天气过程强对流云判识的准确性,结果表明：单时次强对流云的识别区域与发生降雨台站一致的准确率为83%;在整个天气过程中,强对流频次分布与降水实况吻合度较高,说明随着对流云团的移动和发展,判识区域与地面降水区域保持一致,验证了判识方法有效,阈值选取合理,可以为监测暴雨天气系统的发生、发展提供支持。     

Airplane investigation of a case of convective cloud bands over the North Sea

During the experiment KONTROL 1985, an interesting case of prefrontal, nonprecipitating cloud bands parallel to the front at distances of about 25 km was observed over the North Sea. Spectral analysis of high frequency airplane measurements is discussed, putting special emphasis on the significance of the resulting spectral signals. A smaller scale roll circulation of a few kilometers wavelength mainly below cloud base could be inferred from these data. The rolls transport momentum downwards, but heat and moisture upwards into the cloud layer where transport is taken over by individual cloud elements. In addition, reasons for the existence, spacing and orientation of the larger scale cloud bands are discussed.     

Use of dust storm observations on satellite images to identify areas vulnerable to severe wind erosion

Blowing dust is symptomatic of severe wind erosion and deterioration of soils in areas undergoing dessication and/or devegetation. Dust plumes on satellite images can commonly be traced to sources in marginally arable semiarid areas where protective lag gravels or vegetation have been removed and soils are dry, as demonstrated for the Portales Valley, New Mexico. Images from Landsat and manned orbiters such as Skylab and the Space Shuttle are useful for illustrating the regional relations of airborne dust plumes to source areas. Geostationary satellites such as GOES are useful in tracking the time-histories of episodic dust storms. These events sometimes go unrecognized by weather observers and are the precursors of long-term land degradation trends. In areas where soil maps and meteorological data are inadequate, satellite images provide a means for identifying problem areas where measures are needed to control or mitigate wind erosion.     

Impact of Saharan dust on landfalling North Atlantic tropical cyclones over North America in September

Using reanalysis data and model simulations, this study reveals an increase in September landfalling North Atlantic tropical cyclones (TCs) during years that have a strengthened Saharan dust plume, and the related physical processes are investigated by analyzing the relationship of dust aerosol optical depth with TC track, intensity, and the related meteorological environment. Suppression of the sea surface temperature (SST) by the Saharan dust plume can hinder TC tracks over the central tropical North Atlantic, inducing westward development of TC tracks to the western tropical North Atlantic with higher SST, which is more conducive to TCs forming major hurricanes. This physical process increases TC landfalls in North America, especially major hurricane landfalls in the continental United States, leading to greater potential destructiveness.摘要本项研究利用再分析数据和模式模拟数据分析了沙尘的气溶胶光学厚度与台风的登陆, 轨迹, 强度及相关气象环境参数的关系, 揭示了9月北大西洋台风的登陆次数会在撒哈拉沙尘较强的年份中增加, 以及这一现象的物理机制. 撒哈拉沙尘对热带北大西洋中部海表温度具有抑制作用, 会阻碍该地区的台风活动, 因此台风只能向西移动进入海表温度较高的热带北大西洋西部, 从而更易于形成强台风. 这一物理过程将导致台风登陆北美大陆的频次增加, 特别是强台风登陆美国的可能性增强, 产生更大的潜在破坏性.     

基于FY-4A卫星数据的强对流云团识别与监测

为解决强对流监测问题,克服地区亮温特征对卫星监测的影响,利用FY 4A卫星L1数据,结合滑动窗口方法和多通道动态阈值自动识别法,对典型强对流云团进行识别与监测。结果表明：1）多通道动态阈值自动识别方法结合滑动窗口方法,可避免人为设置阈值的主观性,整合强对流的区域识别结果,实现全国强对流云团监测。2）此方法具有良好的强对流云团识别效果,识别正确率达到89%;3）FY 4A卫星识别结果与雷达反射率高值区基本一致,能够准确监测强对流云团发生发展和移动的过程,具有较高的识别精度。     

Formation and evolution of mesoscale convective systems that brought the heavy rainfall over Seoul on September 21, 2010

An investigation has been carried out using observational data and a numerical model to explain the formation and development of heavy precipitation systems on September 21, 2010. These systems were responsible for heavy rainfall over the middle Korean peninsula, with a maximum 24-h rainfall amount greater than 290 mm in the Seoul metropolitan area. Both observational analysis and a numerical simulation indicate that an important starting condition for this heavy rainfall event is the presence of a pressure trough over the Shandong peninsula and the Yellow Sea. Convective cells formed in the early morning over this trough area, grew into larger systems as they moved eastward, and induced the formation of a meso low over the Yellow Sea around 0000 UTC on September 21, 2010. A stationary front with significant vertical circulation developed in response to the deformation of flow associated with the meso low. In the meantime, multicell-type convective systems continuously developed and moved along the front. These storms developed further and produced heavy rainfall over the middle Korean peninsula, which includes the Seoul metropolitan area. According to observations, the band structure appeared to change after 0700 UTC as a narrow convection band developed over the sea, upstream of the existing band of multicell storms. Numerical simulation showed a similar transition. However, it failed to reproduce the stationary behavior of the observed band.     

青藏高原那曲地区一次深对流云垂直结构的多源卫星和地基雷达观测对比分析

为了加强对青藏高原深对流云垂直结构的深入认识,利用TRMM、CloudSat和Aqua多源卫星观测资料及地基垂直指向雷达（C波段调频连续波雷达和KA波段毫米波云雷达）资料,对第三次青藏高原大气科学试验期间2014年7月9日13-16时（北京时）发生在那曲气象站附近的深厚强对流云和那曲气象站以西100 km左右的深厚弱对流云的垂直结构特征进行了分析,得到的结果如下:（1）深厚强对流云和深厚弱对流云的水平尺度均较小（10-20 km）,垂直发展高度较高（15-16 km,均指海拔高度）;深厚强对流云在0℃层以下雷达反射率因子递增非常快,表明对流云内固态降水粒子下落至0℃层以下后融化过程有很重要的作用;在对流减弱阶段有明显的0℃层亮带出现,亮带位于5.5 km左右（距地1 km）;（2）对比TRMM测雨雷达和C波段调频连续波雷达观测到的雷达反射率因子,发现TRMM测雨雷达在11 km以下存在高估;（3）深对流云主要为冰相云,云内10 km以上主要是丰富小冰粒子,而10 km以下是较少的大冰晶粒子;深厚强对流云和深厚弱对流云的微物理过程都主要包括混合相过程和冰化过程,混合相过程分为两种:一种是-25℃（深厚强对流云）或-29℃（深厚弱对流云）高度以下以凇附增长为主,另一种是该高度以上主要以冰晶聚合、凝华增长为主,该过程冰晶粒子有效半径增长较快。这些空基和地基的观测证据进一步揭示了青藏高原深对流云的垂直结构特征,为模式模拟青藏高原深对流云的检验提供了依据。      

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...     

暴雨模拟中积云对流参数化方案的对比试验

基于中尺度数值预报模式WRF V3.5,利用7种积云方案和13种云微物理方案构成的不同组合设计了91组试验,对2014年第10号台风“麦德姆”登陆后影响江西期间的路径进行了模拟和分析。结果发现,台风路径对积云和微物理方案的选择较为敏感,在91组模拟试验中,模拟路径与实况路径的偏差从29.7~76.9 km不等,平均偏差为54.5 km;Grell-Freitas积云方案与WDM5和WDM6微物理方案的组合(N38和N39)模拟的台风路径最为接近实况路径(偏差约30 km),而BMJ积云方案与Kessler、SUB-YLin和Milbrandt微物理方案的组合(N14、N22和N24)的模拟较差,模拟路径与实况路径偏差超过75 km,且明显较实况偏东;对于某一积云(微物理)方案,13种微物理(7种积云)方案的表现也有较大差异,总体上Grell-Freitas和Grell-3方案在7种积云方案中表现最好,而WDM5和WDM6则在13种云微物理方案中表现最好;N38和N39试验成功模拟了台风路径的主要原因是较好地模拟出西太平洋副热带高压(以下简称西太副高)的位置,而N14、N22和N24试验模拟的台风路径偏东则主要是由模拟的西太副高位置偏东造成。