云南省闪电活动时大气相对湿度结构特征

利用2007年6月1日—8月31日云南省闪电定位系统监测的云-地闪电资料与NCEP/NCAR再分析资料中的相对湿度物理量,分析了云南省闪电活动时相对湿度的结构特征。结果表明:云南省闪电活动除具有夏季是高发期且日分布具有呈一峰一谷变化特征,在时间演变上还具有不均匀和阶段性的特点,这与特定的大气相对湿度环境条件密切相关;云南省闪电活动一般发生在相对湿度垂直结构具有低层湿度不高、中层高湿、高层又逐渐变干的环境大气中,大约在中层700 hPa以下相对湿度随高度增加,逐渐在中层形成高湿层,中层以上相对湿度又随高度减小,低层湿度不高、中层高湿、高层偏干的环境相对湿度条件非常有利于雷暴天气的发生和闪电的形成,一方面中层以下水汽随高度增加有利于水汽的上升运动和云的凝结形成,另一方面中高层水汽随高度迅速减小有利于形成上干下湿的大气对流不稳定,促使对流云进一步发展,从而产生闪电活动;低层相对湿度在40%～75%之间,中层600～700 hPa之间相对湿度较高,可达80%以上,一般为90%～95%,中层湿层越深厚,闪电过程越强烈,在高层250～400 hPa左右相对湿度减小到35%～60%之间。     

松嫩平原西部局地暴雨天气成因分析

利用常规气象观测、卫星、雷达和NCEP1°×1°再分析等资料,分析2013年6月27~28日齐齐哈尔市稳定性中雨和龙江县对流性暴雨天气成因,结果表明：龙江短时强降雨出现在850hPa切变线同500hPa槽线或850hPa干线位置近于重合时,层结不稳定,上升运动强;齐齐哈尔降雨发生在低层切变线附近,层结趋于稳定,上升运动弱。地形迎风坡作用有利于龙江降雨强于齐齐哈尔。 单站风、相对湿度和垂直速度时空变化差异以及对流有效位能、大气可降水量和SI指数等物理量可以反映两地上升运动、水汽、层结不稳定条件差异。较好的水汽和大气层结不稳定条件只是对流性短时强降水的必要条件。中尺度对流云团和小尺度对流云回波产生龙江短时强降雨,齐齐哈尔稳定性较大降雨由层状云产生。     

2012年早春广西高架雷暴冰雹天气过程分析

利用常规观测资料和雷达资料,对2012年早春广西高架强雷暴冰雹天气过程进行分析,得出以下结论:(1)冰雹伴随雷暴发生在地面锋后约1000 km,边界层为冷高压控制.850 hPa风速较小,700 hPa以上层有强急流,700～850 hPa有强的垂直风切变,500 hPa高空冷槽东移为对流的发生提供触发条件.(2)冰雹发生在850 hPa切变线南北两侧约200 km范围,等压面锋区强度大;高空槽前正负变温使700～500 hPa垂直方向温度差大,导致层结对流不稳定性加大.当500 hPa低槽移至强锋区上空时,锋面坡度变陡,上升运动加强,不稳定性增大,使得冰胚在对流层中层增长而形成冰雹.(3)风暴追踪信息显示风暴生成高度高,在垂直方向上倾斜增长;质心均在5～6 km,风暴生成后,随着时间的推移逐渐向低层发展,最大反射率以及液态含水量均不大,具有明显高架雷暴特征.     

Statistical characteristics of environmental parameters for warm season short-duration heavy rainfall over central and eastern China

Water vapor content,instability,and convergence conditions are the key to short-duration heavy rainfall forecasting.It is necessary to understand the large-scale atmospheric environment characteristics of shortduration heavy rainfall by investigating the distribution of physical parameters for different hourly rainfall intensities.The observed hourly rainfall data in China and the NCEP final analysis（FNL）data during 1May and 30 September from 2002 to 2009 are used.NCEP FNL data are 6-hourly,resulting in sample sizes of 1573370,355346,and 11401 for three categories of hourly rainfall（P）of no precipitation(P<0.1 mm h^-1),ordinary precipitation(0.1≤P<20 mm h^-1),and short-duration heavy rainfall(P≥20.0 mm h^-1),respectively,by adopting a temporal matching method.The results show that the total precipitable water（PWAT）is the best parameter indicating the hourly rainfall intensity.A PWAT of 28 mm is necessary for any short-duration heavy rainfall.The possibility of short-duration heavy rainfall occurrence increases with PWAT,and a PWAT of 59 mm is nearly sufficient.The specific humidity is a better indicator than relative humidity.Both 700-and 850-hPa relative humidity greater than 80%could be used to determine whether or not it is going to rain,but could not be used to estimate the rainfall intensity.Temperature and potential pseudo-equivalent temperature are also reasonable indicators of short-duration heavy rainfall.Among the atmospheric instability parameters,the best lifted index（BLI）performs best on the shortduration rainfall discrimination;the next best is the K index（KI）.The three rainfall categories are not well recognized by total totals（TT）or the temperature difference between 850 and 500 hPa（DT85）.Threequarters of short-duration heavy rainfall occurred with BLI less than-0.9,while no short-duration heavy rainfall occurred when BLI was greater than 2.6.The minimum threshold of KI was 28.1 for short-duration heavy rainfall.The importance of dynamic conditions was well demonstrated by the 925-and 850-hPa divergence.The representativeness of 925-hPa divergence is stronger than that of 850 hPa.Three-quarters of short-duration heavy rainfall occurred under a negative divergence environment.However,both the best convective potential energy（BCAPE）and vertical wind shear were unable to discriminate the hourly rainfall intensities.     

中国西部空中水汽分布结构特征

利用1958-1997年月平均NCEP比湿资料研究了中国西部空中水汽分布特征。结果表明：水汽的垂直分布结构非常相似，850hPa以上的水汽分布中心位于青藏高原上空，5-10月水汽含量主要集中在500hPa以下，其中7月的空中水汽含量最丰沛。水汽含量随高度减少，从季节变化来分析，夏季最大、秋季次之、冬季最小。40a的水汽年代际变化表明，夏季空中水汽含量呈现线性下降趋势，特别是20世纪90年代以来更明显；冬季比湿呈线性上升趋势，1月和7月比湿的年代际变化趋势呈反位相特征。     

On the relationship between Arabian Sea warm pool and formation of onset vortex over east-central Arabian Sea

The interannual variability in the formation of mini warm pool (MWP, SST ≥ 30.5°C) and its impact on the formation of onset vortex (OV) over the east-central Arabian Sea (ECAS) are addressed by analyzing the NCEP OIV 2-weekly SST data and NCEP–NCAR reanalysis 850 hPa wind fields from May to June (prior to the onset of monsoon) over the north Indian Ocean for a period of 12 years from 1992 to 2003. Strong interannual variability in the formation and intensification of MWP was observed. Further, the 850 hPa wind fields showed that OV developed into an intense system only during 1994, 1998 and 2001. It formed in the region north of the MWP and on the northern flank of the low-level jet axis, which approached the southern tip of India just prior to the onset of monsoon, similar to the vortex of MONEX-79. The area-averaged zonal kinetic energy (ZKE) over the ECAS (8–15°N, 65–75°E) as well as over the western Arabian Sea (WAS, 5°S–20°N, 50–70°E) showed a minimum value of 5–15 m² s^?2 prior to monsoon onset over Kerala (MOK), whereas a maximum value of 280 m² s^?2 (40–70 m² s^?2) was observed over the ECAS (WAS) during and after MOK. The study further examined the plausible reasons for the occurrence of MWP and OV.     

一次非典型暴雨中的MCSs特征及其形成条件

利用多种数据对2014年6月3～4日暴雨中的MCSs进行分析,结果表明:MCSs活动呈现出多尺度特征及多样化结构,即在中α－MCSs尺度中嵌套着中β－MCSs和中γ－MCSs,在形态上呈“椭圆”型和“带状”型,旧云团相互合并诱发出新的对流体是其活动的显著特点。在时间演变上,MCSs活动大致分为两个阶段,第一时段活动造成盆地南部和东北部的暴雨天气,第二时段活动造成盆地西部至南部的大雨到暴雨天气。分析MCSs的形成原因进一步表明,MCSs的发展与850hPa盆地倒槽和暖湿南风气流极为密切,在对流层中部影响系统不明显的形势下,850hPa倒槽及急流附近的湿、热环境及不稳定层结为对流提供了有利条件,如较大的CAPE值和上干下湿的湿度结构,K指数36℃以上,LI为负,且非地转湿Q矢量散度为负,这一序列物理量变化均是触发MCSs生成的重要因子。      

基于物理量场异常度的四川暴雨集合预报释用分析

根据四川区域暴雨的定义,筛选2012~2016年的区域暴雨过程,选取850hPa的比湿(q)、850hPa经向风(v)2个因子,并应用NCEP资料计算30年的气候平均值和气候标准差,引入集合预报资料,计算四川暴雨个例各要素的标准化异常度和异常度概率。得到以下结论:(1)850hPa的比湿(q)、850hPa经向风(v)两个因子的48h集合最大预报异常度对四川盆东型暴雨更为适用,实况50mm以上降水落区一般都发生在850hPa比湿(经向风)异常度大值区,而对盆西型暴雨适用性不好;(2)在四川盆东型暴雨中,60%暴雨个例的实况暴雨中心,850hPa上比湿超出气候平均1个标准差的概率达到80%以上,超出1.5个标准差的概率到达50%以上。      

山东半岛南部一次沿海强降雨成因分析

利用常规气象观测资料、区域自动站观测资料、NCEP/NCAR 1°×1°再分析资料和雷达探测等资料,对2012年9月21日山东半岛南部沿海强降雨过程的成因进行了天气学诊断分析,结果表明:1强降雨是在500hPa第1个西风槽过后第2个西风槽逼近的过程中产生的,850hPa以下为偏南的向岸风,且风速随时间增大,形成偏南的超低空急流,持续地向沿海输送水汽和能量,造成水汽辐合、湿度增大、对流有效位能升高。产生强降雨的水汽和不稳定能量条件远小于内陆地区。2在向岸的超低空急流的左侧产生中小尺度的涡旋和辐合上升,海岸地形抬升作用使得上升运动加强,触发对流不稳定能量释放,造成强降水。3在雷达回波中,小尺度的对流单体沿海岸线向西南方向发展,后期在日照附近的沿海形成弓状回波,向东南海区移动。     

基于多源资料的一次暖区暴雨水汽特征分析

利用常规气象观测资料、NCEP逐6 h再分析资料(1°×1°)、微波辐射计资料以及HYSPLIT模式等,对2021年7月5日冀中平原一次暖区暴雨过程的水汽输送特征进行对比分析。结果表明：应用HYSPLIT模式模拟分析后发现,本次过程中925和850 hPa降水开始前比湿在12 g/kg以上,是暴雨区的主要水汽贡献者,其主要水汽通道为西南路径,水汽贡献率分别占57.57%和63.64%。源自黄海或途径黄海、渤海等地的气块在东南转西南气流的引导下为暴雨区低层带来丰富的水汽,同时源自亚欧大陆中高层的气块,随着西风带长波槽脊的运动,为暴雨区上空500 hPa带来干空气,构成上干下湿的不稳定层结。降水开始前,925和850 hPa在相应引导气流的作用下,水汽不断向冀中平原输送,使得优良的水汽条件主要集中于低层大气,与HYSPLIT模式模拟结果一致。通过微波辐射计对降雨过程的水汽特征进行分析,结果表明在降雨开始前,700 hPa以下高度的水汽含量有明显增加,水汽密度最大达到14 g/m³。分析3种不同资料得到相似结论,但HYSPLIT模式和微波辐射计两种高时空分辨率资料的应用...     

四川地区对流参数与雷电活动的相关关系

本文利用2013年和2014年7～8月NCEP1°×1°再分析数据和四川省雷电监测网观测资料,统计分析了雷电活动发生前最佳近地表四层(1000hPa、975hPa、950hPa和925hPa)等压面抬升指数、对流有效位能、K指数和850hPa假相当位温与雷电活动的相关关系。通过此次研究发现,对流参数在有雷电过程和无雷电过程中有明显差异,并且发现这四个对流参数和四川省雷电活动有较好的相关关系。通过此次研究得到了四川地区雷电活动对流参数预报指标,对已有雷电潜势预报有一定的参考价值。      

南印度洋热带气旋生成频数气候变率对海温异常模响应的研究

基于1980—2014年的哈德莱中心海冰及海温的月平均SST资料,美国联合台风警报中心(JTWC)的best-track资料以及NCEP/NCAR再分析月平均资料,利用广义平衡反馈方法(GEFA)研究南印度洋热带气旋(TC)生成频数对海表温度异常的响应特征。研究表明:(1)南印度TC生成频数对北太平洋第一模态(NP1)和热带大西洋第二模态(TA2)有显著响应,分别通过了置信度为99%和96%的Monte-Carlo检验,对应的响应振幅分别为0.67和0.49。(2)局地环境要素对关键SSTA模的GEFA响应结果显示:当NP1出现类似于太平洋年代际振荡(PDO)的正位相时,850 h Pa相对涡度在15°S附近的印度洋海域上都有一个自西向东的显著正响应带,垂直风切变在马达加斯加以东的大部分海域都表现为显著的负响应,600 h Pa相对湿度在马达加斯加以东的部分海域表现为显著的正响应;当TA2对应的时间系数为正异常时,850 h Pa相对涡度和600 h Pa相对湿度在澳大利亚的西北部印度洋海域表现为显著的正响应,垂直风切变在澳大利亚的西北部印度洋海域表现为显著的负响应。     

偏东风冷空气与地形相互作用背景下北京局地强降水成因分析

综合使用自动站、卫星TBB、探空、BJ-ANC雷达拼图、雷达变分同化分析系统（VDRAS）风场以及NCEP/GFS0.5°×0.5°分析资料,对漏报的2013年6月4日白天北京局地强降水天气过程及成因进行详细分析。结果表明：（1）该过程是在弱天气尺度背景（即没有明显西来槽和高空冷空气等天气尺度系统强迫）下产生的,且北京地区低层被由渤海湾侵入的偏东风（冷空气）控制,大气层结上暖下冷,有别于通常意义上的夏季强对流天气发生背景,因此造成其预报失误。（2）高空正涡度平流提供了一定的动力条件,但不足以触发强对流,其主要触发机制是低层偏东风冷空气侵入以及暖湿空气在冷空气和地形相互作用下强迫抬升,这一点在今后强对流预报中尤须关注。（3）当夏季早晨850 h Pa以下出现逆温层时,若当日白天太阳辐射升温状况良好,08时探空资料在使用时应进行订正,T-logp图订正后显示北京具有显著对流有效位能（CAPE）;此外,较大的中低层垂直风切变和边界层内较大的湿度层结均为雷暴下山后明显增强并造成局地强降水提供了有利的环境条件。（4）雷暴前侧出流与东南风形成的辐合线造成了中尺度对流单体不断东移。     

江西秋季一次区域性强对流天气过程的模拟分析

利用常规地面观测资料、卫星辐射率资料以及NCAR/NCEP再分析资料,采用中尺度数值模式WRF及其三维变分同化模块,对2009年11月9日江西的一次区域性秋季强对流天气过程进行数值模拟,探讨了此次强对流天气过程发生发展的物理机制。结果表明:(1)江西省基本均处于K指数大于36℃高值区,具备热力不稳定能量,K指数很好地反映此次过程的热力条件;(2)强的垂直风切变,为此次强对流提供发展的能量;(3)Δt850-500达到26℃,具有强垂直温度梯度;(4)此次强对流过程中,对流层中高层的干侵入可以向下伸展至700 hPa高度层以下,有利于对流不稳定能量在低层的积聚,对流不稳定能量的释放可以将低层的暖湿气流向上输送至较高的层次,加强了强对流天气的发生。     

基于集合预报极端天气预测指数的浙江分类强对流预报模型

利用2016—2021年ECWMF集合预报资料、浙江自动站实况资料等,计算浙江短时强降水、雷暴大风和冰雹等强对流天气相关物理量的极端天气预报指数（EFI：Extreme Forecast Index）,分析EFI分布特征,并构建了分类强对流预报模型。结果表明：强对流天气与物理量的EFI有密切联系,发生短时强降水时,对流有效位能、整层可降水量、850 hPa与500 hPa温差和位温差的EFI较大,而垂直风切变的EFI为负值,因而较小的垂直风切变更有利于出现极端降水;发生雷暴大风和冰雹时,对流有效位能、850 hPa与500 hPa温差和位温差以及850 hPa温度露点差的EFI较大,700 hPa露点温度的EFI为负值,与上层干冷下层暖湿的有利层结条件有关。利用支持向量机多分类方法,将强对流天气相关物理量的EFI作为特征值开展训练,构建的预报模型对于非局地强对流天气有较好的预报效果,其中短时强降水的误判率明显低于雷暴大风。     

Selected instability indices in Europe

A climatology of various parameters associated with severe weather and convective storms has been created for Europe that involves using radiosounding data collected at the University of Wyoming for the period from 1991 to 2005. The analysis is based on monthly means, frequency distributions of such parameters as convective available potential energy (CAPE), convective inhibition energy (CIN), KI - index, total totals index (TTI), and the severe weather threat index (SWEAT). Monthly average CAPE values exceeding 300 Jkg^?1 are observed over the west Mediterranean Sea and the neighboring coastal countries. The similar seasonal cycle and spatial distributions exhibit CIN fields with summer monthly means above 100 Jkg^?1 observed on the south part of the researched domain. The KI, TTI, and SWEAT indices, which assess both the lapse ratio between 850 and 500 hPa and low level humidity, show the privileged region (the Alpine area and the Carpathian Basin) with the highest instability conditions. Orography clearly plays an important role in this structure. Farther from this area, the monthly average decreases to the east, west, north, and south of the research domain. Ward’s procedure was applied to create objective regionalization according to instability conditions. This method tends to produce two regions with relatively different instability conditions and few subregions with similar conditions. The first region, covering the Alpine area, the west Mediterranean Sea, west Turkey and the southern Ukraine, is characterized by the highest instability. The rest of the investigated area is the second region with a more stable atmosphere.     

2019年6月上旬江西一次持续性暴雨天气过程成因

利用常规气象观测资料、FY-2G卫星TBB资料和NCEP/NCAR再分析资料,基于HYSPLIT模式,对2019年6月6—10日影响江西的一次持续性暴雨过程成因进行初步分析。结果表明： 1） 此次暴雨过程是一次大范围的持续性暴雨,产生于对流性不稳定环境场。暴雨区上空中层多短波槽活动,受槽后偏北气流影响,干冷空气叠加在低层暖湿气流之上,导致暴雨过程的发生。2） 暴雨落区主要位于低层850 hPa高度层的急流前端12—16 m/s的风速区内。3） 高空偏北气流的强弱在700 hPa高度层的风场和降水气块轨迹来源变化上有所体现。700 hPa高度层的假相当位温大于348 K的高温高湿区与正涡度区基本吻合,其位置对未来6 h的降水落区有一定的指示意义。     

夏季低压控制下黄海西北部海域海雾发生气象条件合成分析

利用瞬变扰动分析的原理,提供了一个可以客观判定海雾发生时天气类型的方法。在分类结果的基础上,对环流形势、散度和垂直速度以及温度湿度的垂直廓线等进行合成分析,得到低空（1 000 hPa）为低压扰动下发生海雾（L型海雾）的环流和物理量场基本特征,并与高压控制下海雾（H型海雾）进行对比,结果表明：1）L型海雾位势高度负异常扰动主要表现在低层,其平均值为-65.66 gpm,向上逐渐减弱;2）L型海雾在发生时其逆温强度小于H型海雾,雾层较厚,雾层上空湿度仍然比较大,而H型海雾雾层上空有比较明显的干层;3）L型海雾在垂直方向上的分布具有三层结构,第一层1 000～950 hPa为辐合伴有弱上升和下沉运动,第二层950～850 hPa为辐散伴有弱下沉运动,第三层850～500 hPa为逐渐加强的上升运动;H型海雾为两层结构,1 000 hPa为辐散伴有弱的上升和下沉运动,950～500 hPa为一致的下沉运动;4）概率密度统计分析进一步定量表明了L型和H型海雾发生时垂直运动以及相对湿度在各层中的分布情况。这些结论对黄海西北部夏季低压环流形势下海雾的预报提供了重要参考。     

Diagnosing deep convection from global analyses

Summary Convection, a sub-gridscale process, is coupled to the gridscale motions via the averaged budget equations. In this study atmospheric convection is represented by the vertical eddy flux of equivalent temperature, referred to asconvective flux. It is demonstrated with a thermodynamic diagnostic model for an atmospheric column (DIAMOD) that the convective flux can, with tolerable error, be diagnosed from daily global gridscale analyses. These yield the gridscale budget of equivalent temperature. The budget is the observable quantity, it is in balance with the unobservable convective flux. We reproduce the known result that in convectively active atmospheric columns the budget is negative in lower and positive in upper layers. The corresponding vertical mean slope of the budget controls the convective strength; the slope is strongly negative for deep convection.In the global mean column the convective flux converges upward throughout the entire atmosphere. In actual convective situations, however, the flux diverges in lower layers, reaches highest intensity somewhere between 700–500 hPa and converges in the upper atmosphere. We find maximum fluxes around 600 W/m² in individual tropical columns and extreme fluxes exceeding 1000 W/m² in midlatitude columns. In the monthly mean however, the convective flux is clearly larger in the tropics; it also reaches to significantly higher levels in the tropics than in midlatitudes. While these qualitative results are invariant against using both routine analysis and reanalysis data from different sources (ECMWF and NCEP) our results change quantitatively when changing the data sources. We attribute this effect to differences in the sub-gridscale parameterization implicit in the objective data assimilation of the weather centres which are not completely removed by the incoming observation data in the final analyses.With 12 Figures     

Modeling the climatic effects of urbanization in the Beijing–Tianjin–Hebei metropolitan area

In this analysis, the weather research and forecasting model coupled with a single-layer urban canopy model is used to simulate the climatic impacts of urbanization in the Beijing–Tianjin–Hebei metropolitan area, which has experienced significant expansion in its urban areas. Two cases examining current landscapes and the sensitivity test of urban areas replaced by cropland have been carried out to explore the changes in the surface air and atmospheric boundary structure. The impact of urbanization on annual mean surface air temperature has been found to be more than 1 °C in urban areas, and the maximum difference is almost 2 °C. The change in near-surface level temperature is most pronounced in winter, but the area influenced by urbanization is slightly larger in summer. The annual mean water vapor mixing ratio and wind speed are both reduced in the urban area. The effect of urbanization can only heat the temperature inside the urban boundary layer, below 850 hPa. The modeling results also indicate that the underlying surface thermal forces induced by the “urban heat island” effect enhance vertical air movement and engenders a convergence zone over urban areas. The convergence at low level together with the moisture increases in the layer between 850 and 700 hPa triggered the increase of convective precipitation.