Analysis of a Beijing Heavy Snowfall Related to an Inverted Trough in November 2009

This paper studies a heavy snowfall in Beijing that took place on 1 November 2009. The date of the snowfall was about one month earlier than the average. The National Centers for Environmental Prediction (NCEP) reanalysis data, conventional data, and Automatic Weather Station (AWS) data are utilized to explore the reasons for the snowfall and the influencing systems. The main conclusions are as follows: (1) It is revealed from the average geopotential height and average temperature fields at 500 hPa that the large scale circulation in November 2009 was favorable to snowfall. The cold-dry air from West Siberia and the warm-moist air from the Bay of Bengal converged in North China. In addition, it was found from the average moisture flux field at 700 hPa that the main water vapor source was in the Bay of Bengal. (2) Not only the "return current", as usually accepted, but also the inverted trough on the current had an important contribution to the snowfall. The inverted trough could produce the obvious upward motion that is an important environmental condition of snowfalls. (3) More attention should be paid to mesoscale systems such as mesolows during the cold season because of their importance, though they do not occur as frequently as in the warm season. It should be pointed out that AWS data are very useful in mesoscale system analysis during both warm and cold seasons.

Aircraft Observation Analysis on Stratiform Cloud Structure near a Low Trough - Inverted Trough

An aircraft precipitation operation and detecting was implemented by Hebei Weather Modification Office over Shijiazhuang City during18:18-19:37 on April 2,2014. The detecting area was near 500 hP a of high-altitude trough and surface inverted trough. Slight shower had appeared in Tianjin( rear of inverted trough) and Shanxi Province( near the inverted trough) at 20:00,while there was not precipitation in Hebei Province which was near the inverted trough. Analysis showed that the water vapor supply was not enough below 550 hP a in south-central Hebei Province,and cloud system development condition was poor. The cold cloud developed better,but there was not warm cloud,causing no precipitation on the ground.

Analysis of the Heavy Rainfall Process in Mangshi City on August 8, 2023

On August 7,2023,Mangshi City,Dehong Prefecture experienced a local heavy rainstorm,and the geological disaster caused by the heavy rainfall caused casualties and property losses.Based on the real-time observation data of automatic stations,Doppler weather radar detection and meteorological risk warning products,the disaster situation,social impact,forecast and early warning service,causes of heavy precipitation and forecast and early warning inspection were summarized and analyzed.The results show that the heavy rainfall was prominent locally,lasted for a long time and accumulated a large amount of rainfall.There were biases in model products,and it was difficult for forecasters to make subjective corrections in complex terrain.The analysis ideas and focus points of heavy rainfall forecast,the improvement ideas and technical schemes of forecast deviation,and the improvement ideas and suggestions of services were summarized.It provides a reference for the forecast and early warning of severe weather in the future.

Analysis of a Rare Heavy Rain Weather Process in Autumn in Ulanqab City

Based on the conventional observation data and NCEP/NCAR reanalysis data,the circulation situation,influencing systems and causes of the heavy rain during September 20-21,2010 in Ulanqab City were analyzed from the evolution process of weather circulation situation and the changes of various physical quantity fields.The results show that there was an obvious frontal zone between 45-52°N,which brought strong cold air.The transport of warm and humid air outside the subtropical high and typhoon was the main water vapor source of the strong precipitation,and the southwest jet at 700 hPa transported abundant water vapor.There was a broad inverted trough to the south of 45°N,with a central value of 1000.0 hPa.Ulanqab City was on the top of the inverted trough,stable and less moved,which was conducive to the occurrence of systematic heavy precipitation.The rainstorm was a strong precipitation process caused by the intersection of cold air brought by the southward movement of the upper frontal zone and warm and humid air outside the subtropical high.After the precipitation,the invasion of strong cold air brought frost and cold wave weather to Ulanqab City.

川南一次准正压类强对流天气的综合分析

就四川而言,相较于斜压大气中的强对流天气,准正压大气中的强对流天气出现概率低,突发性更强,监测和预报难度更大。本文基于气象站观测资料、雷达组合反射率拼图、气象卫星的TBB资料以及NCEP和ERA5再分析资料,运用天气学、卫星气象学和雷达气象学方法,对2022年8月5日四川南部地区发生的准正压类强对流天气进行了综合分析。结果表明:本次强对流天气以雷暴大风和短时强降雨为主,持续时间约2 h,其间气象要素变化剧烈;主要影响系统为高层的南亚高压、中低层的季风低压倒槽和地面热低压;高CAPE值、“上干下湿”的湿度层结、弱垂直风切变、低层辐合、高层辐散和深厚的上升运动是强对流天气出现的有利环境条件;低压倒槽前的云带在川南演变为对流云团,多中心带状雷暴群的NE段在川南演变为团状雷暴群,雷暴大风和短时强降雨与冷云中心、高TBB梯度、高反射率梯度、反射率大小及其维持时间存在较好的对应关系。

A Study on a Heavy Rainfall Event Triggered by an Inverted Typhoon Trough in Shandong Province

A heavy rainfall event that occurred in Shandong Province in 26 28 August 2004 was caused mainly by Typhoon Acre and cold air activities related to a westerly trough. The event was triggered by an inverted typhoon trough, which was closely associated with the intensification of the low-level southeasterly flow and the northward transport of heat and momentum in the periphery of the typhoon low. A numerical simulation of this event is performed using the nonhydrostatic mesoscale model MM5 with two-way interactive and triply-nested grids, and the structure of the inverted typhoon trough is studied. Furthermore, the formation and development mechanism of the inverted typhoon trough and a mesoscale vortex are discussed through a vorticity budget analysis. The results show that the heavy rainfall was induced by the strong convergence between the strong and weak winds within the inverted typhoon trough. Dynamic effects of the low-level jet and the diabatic heating of precipitation played an important role in the development of the inverted typhoon trough and the formation of the mesoscale vortex. The vorticity budget analysis suggests that the divergence term in the low troposphere, the horizontal advection term, and the convection term in the middle troposphere were main contributors to positive vorticity. Nonetheless, at the same pressure level, the effect of the divergence term and that of the adveetion term were opposite to each other. In the middle troposphere, the vertical transport term made a positive contribution while the tilting term made a negative contribution, and the total vorticity tendency was the net result of their counteractions. It is found that the change tendency of the relative vorticity was not uniform horizontally. A strong positive vorticity tendency occurred in the southeast of the mesoscale vortex, which is why the heavy rainfall was concentrated there. The increase of positive vorticity in the low （upper） troposphere was caused by horizontal convergence （upward transport of vorticity from the lower troposphere）. Therefore, the development of the inverted typhoon trough and the formation of the mesoscale vortex were mainly attributed to the vorticity generated in the low troposphere, and also the vertical transport of vorticity from the low and middle troposphere.

NUMERICAL SIMULATION OF EXTREMELY HEAVY RAIN AND MESO-β SCALE LOW VORTEX IN INVERTED TYPHOON TROUGH

Large-scale and mesoscale analyses are made for extremely heavy rain (EHR) and meso-β scale low vortex (MSLV) in Jiading District of Shanghai Municipality during 6-7 July 2001.It is shown that the EHR forms in the situation of northern westerly trough linking together with southern inverted typhoon trough at northwest side of the West Pacific Ocean subtropical high. Numerical simulation is made using a 21-layer improved REM (regional η coordinate model) for this course.The results show that the precipitation forms earlier than MSLV.and the strong convergence in wind velocity mate (WVM) triggers the strong precipitation.The formative reasons of WVM.especially the weak wind velocity center are discussed,and the formative mechanisms of the MSLV and EHR are discussed using high spatial and temporal resolution model- output physical fields.The results show that the heavy rain releases latent heat and warms the air column,and enhances the low level positive vorticity that existed before.Then it causes the formation of MSLV.There is a positive feedback mechanism between low vortex and precipitation,so CISK must be an important mechanism.

呼伦贝尔市2次强降水过程对比分析

利用常规观测资料、NCEP再分析资料,对呼伦贝尔市2022年7月4-9日和7月12-15日2次降水过程进行了对比分析,从大气环流背景和动力条件等方面探究了2次降水过程成因异同。结果表明:2次降水均呈现出降水持续时间长、范围广、强度大、局地性强的特点,其中4-9日过程影响系统为高空冷涡配合中低层低涡切变线,且系统较为垂直,地面为配合冷暖锋的地面气旋;而12-15日为高空冷槽影响,且中低层的低涡切变和中高层的冷槽有一定距离,即冷暖空气交汇面大,地面受气旋顶部倒槽影响。

一次冷锋倒槽暴风雪过程特征及其成因分析

利用常规观测资料,对2010年3月14日山西中北部的一次冷锋倒槽暴风雪天气的风场结构及其形成和维持机制进行了探讨。结果表明:(1)此次过程分为4个阶段,其中强冷锋降雪持续时间长,出现了两次降雪增幅,而涡旋降雪时间短,但强度大;地面自动站风场上β-中尺度辐合和β-中尺度涡旋是造成此次暴雪的直接原因。降雪强度和落区与风场结构和高低空系统配置密切相关。(2)变形诊断揭示,500hPa总变形对地面锋生作用明显;伸缩变形项大值中心与地面涡旋中心吻合,是造成地面涡旋加强,产生强降雪的重要机制;对强冷锋降雪而言,切变变形项贡献大于伸缩变形项,切变变形大值区的出现和维持是700hPa低涡切变线和地面强冷锋稳定维持的重要因素。(3)强降雪前12h,高层有暖平流输入,而低层形成"湿冷垫",对低空低涡的发展起着重要作用。(4)强降雪出现前,高空西风急流在300hPa形成急流核,随着急流核的下传,低空低涡发展,切变线稳定维持,导致强降雪持续;强降雪落区和强度与高低空急流轴的位置和急流强度关系密切。

台风残涡北上引发东北地区北部大暴雨的中尺度特征分析

使用常规观测资料、卫星云图、雷达回波资料、自动气象站降水量以及0. 25°×0. 25°的NCEP/NCAR再分析资料,对1710号台风"海棠"残余环流北上引发的东北地区北部的大暴雨过程进行中尺度特征分析。结果表明,台风残余环流移入东北地区后再度加强。地面上负变压中心位于气旋北侧倒槽切变处,气旋的快速发展和加强的变压风辐合,造成低层辐合加强,导致大暴雨的出现。暴雨区呈带状分布,出现向北增强的趋势,在时空分布上都有明显的中尺度特征。探空分析显示暴雨区大气处于不稳定状态,有利于以短时强降水为主的对流发展。暴雨是由MCS活动造成的,每次短时强降水均与TBB低值中心相对应,并滞后1 h左右。对流云团自南向北传播,暴雨主要出现在冷云区内或是云团后部边缘TBB大梯度区处。雷达回波的后向传播造成暴雨区一直有强回波活动,降水持续时间长;强降水是暖云降水,降水效率高,雨强大。引发暴雨的中尺度对流系统具有深厚的垂直运动,加强了低层热量和水汽的向上输送。中低层正涡柱迅速增强,水汽辐合增强,加强了中尺度对流系统的发展和持续时间。中高层有干冷空气活动,不仅触发对流,而且大大降低了大气稳定度,为对流的发生、发展提供了有利条件。

由台风低压倒槽引发的山东暴雨过程研究

2004年8月26—28日发生在山东省的大到暴雨过程主要是由"艾莉"台风减弱的低压和西风带冷空气远距离相互作用造成的,台风倒槽的发展与低空东南气流的加强及台风低压外围热量和动量的向北输送密切相关。采用双向三重嵌套网格非静力模式MM5对这一过程进行了数值模拟,研究了台风倒槽的中尺度结构特征,并通过涡度收支探讨了台风倒槽及中尺度低涡发生发展的物理过程。结果表明,强降水是在台风倒槽顶部强风中心与弱风中心之间的强辐合作用下触发的,台风倒槽的增强和中尺度低涡的形成是低空急流及其动力作用的结果,降水的非绝热加热也起着重要作用。涡度方程的收支诊断表明,对流层低层的散度项、对流层中层的水平平流项和铅直输送项是正涡度的主要贡献者,在同一等压面上散度项和水平平流项的作用是相反的。对流层中层铅直输送项的贡献为正,扭转项为负贡献,涡度变化的总趋势是它们相互作用的净结果。等压面上相对涡度的变化趋势并不是均匀的,中尺度低涡的东南象限相对涡度局地变化较强,这是强降水发生在此的重要原因。低层正涡度的增加是由水平辐合引起的,而高层正涡度的增加是涡度由低层向高层垂直输送的结果。因此台风倒槽的发展和中尺度低涡的形成主要是由于低层的涡度制造,另一方面来自中低层涡度的垂直输送。

台风倒槽内β中尺度低涡及特大暴雨的数值模拟

对 2 0 0 1年 7月 6～ 7日上海嘉定特大暴雨及β中尺度低涡进行大、中尺度分析 ,认为特大暴雨是在西太平洋副热带高压的西北侧、北部西风槽与南部台风倒槽相连的形势下形成的。利用改进的区域 η坐标模式 (REM)对这一过程进行了数值模拟 ,发现降水先于 β中尺度低涡形成 ,强降水是在“风速偶”之间的强辐合作用下触发的。探讨了“风速偶”特别是弱风中心形成的原因。根据模式输出的高时空分辨率物理量场对 β中尺度低涡与特大暴雨的形成进行分析 ,探讨了它们形成的机制 ,结果表明 β中尺度低涡的形成是由于强降水使气柱增暖加强了低空原有的正涡度的情况下形成的 ,低涡与降水存在正反馈机制 。

一次弱对流引发局地特大暴雨天气的诊断分析

对2003年8月28～29日宁陕特大暴雨过程诊断分析结果表明:特大暴雨发生在低层辐合、高层辐合,不利于强对流发展的弱对流环境中。低层850～700hPa低涡倒槽为特大暴雨提供了辐合上升运动和充沛的水汽条件。850hPa几股来自不同方向、性质不同的气流相汇在宁陕上空,强水汽辐合是特大暴雨形成的主要原因。

一次远距离台风影响下的对流性暴雨分析

用常规地面高空观测、中尺度自动气象站、卫星云图以及NCEP的1°×1°再分析资料,对2011年10月13—14日江西省南部出现的区域性暴雨过程进行分析。结果表明:(1)此次降水过程是中纬度西风槽与台风倒槽相互作用的结果,槽前正涡度平流与低层台风倒槽东侧正涡度平流同位相叠加,增强了中低层动力抬升条件,台风东侧的偏南气流将水汽输送到暴雨区;(2)高空槽携带干冷空气入侵与低层台风倒槽的暖湿气流叠加增强了大气的不稳定性,同时中高层有干空气侵入,高空位涡异常下传和低层位温异常利于气旋的发生和发展;(3)地面非均匀加热使得强暴雨区地面出现异常负变压中心,形成变压风辐合和地面中尺度涡旋,触发对流性强降水;(4)该过程共有3个云团产生,中尺度对流云团在地面能量锋区南侧发生,沿能量锋区东移合并,经过高能中心时得到强烈发展。

台风海棠远距离暴雨中尺度系统特征

利用常规探空、加密地面资料、卫星云图和新一代天气雷达产品资料,对2005年7月22日台风海棠倒槽形成的大暴雨天气进行诊断分析。结果表明:(1)台风北伸倒槽与西风带弱冷空气结合造成了这次大暴雨过程,是典型的中低纬系统相互作用过程。(2)倒槽东侧东南低空急流从低纬海上为大暴雨区输送了丰富的热量和水汽,同时,在它的左前方成为强中尺度对流系统发生的源地。(3)高层反气旋的增强,加强了高空的抽气效应,使辐合上升加强,暴雨增幅。(4)卫星云图上,团状的、密实的强中β尺度对流系统的形成和维持是造成短时强暴雨的直接原因。(5)多普勒雷达反射率因子场上,多条中尺度回波带的汇合使回波增强,暴雨增幅。(6)暴雨发生期间,多普勒雷达径向速度场表现明显的水平风场的非均匀性,表现为中低层大范围强辐合风场;风向的垂直方向不连续性,主要表现在风的垂直切变大,风的垂直切变可以为对流云的发展提供动能,有利于大雷暴云的发展和暴雨的形成;逆风区多次出现在风速较大的入流区中并做气旋性旋转北上与正速度区合并,逆风区附近及所经途中出现强回波,暴雨增幅。

一次热带风暴外围特大暴雨分析

运用T1 0 6数值预报产品、天气实况及卫星云图等非常规资料,对1 999年9月4日在远离990 9热带风暴中心的温州引发的特大暴雨进行探讨,发现秋季在厦门以南至广东东部登陆的台风,在浙中南沿海形成台风倒槽,该倒槽内暖湿切变线的中尺度对流云团是引起特大暴雨的重要条件。

2011年山西省一次连续性降雪过程成因分析

利用NCEP/NCAR(1°×1°)逐日6 h再分析资料和常规观测资料,分析了2011年2月25-28日山西的一次连续降雪天气过程。结果发现:此次降雪过程经历了3个阶段,分别是2月25日的倒槽冷锋降雪阶段,26-27日的回流降雪阶段,28日的低空切变降雪阶段。过程涵盖了华北地区大到暴雪的3个类型,分别是倒槽冷锋类、回流类、低空切变线类。25-27日的降雪属东路冷空气影响,28日的降雪则由西北路径冷空气影响所致。暴雪过程有不同的影响系统,26日的暴雪天气是850 hPa东北急流、700 hPa西南急流及暖切变和边界层切变线共同作用的结果,28日的暴雪天气则是500 hPa西北冷平流和西南暖平流导致的地面锋生以及700 hPa暖切变共同作用的结果,条件性对称不稳定是28日降雪维持的机理。对于低空切变类暴雪天气,对流层中层湿核的出现与消失对降雪的开始和结束有较好的指示意义;对于回流类暴雪天气,低层回流对降雪起到了冷垫作用,低空东北急流、西南急流的建立使降雪增幅。26日受东路冷空气影响的回流降雪,从形势特征和高低空配置的完整性分析,预报员相对容易预报暴雪的落区和强度。28日在西北路径冷空气影响下产生的暴雪天气是一个预报难点,对这类天气的预报需关注暖湿空气的活动及其维持机制,假相当位温低谷期的开始对降雪的预报有12～24 h的提前量。

一次回流与倒槽共同作用产生的暴雪天气分析

对2006年1月18—19日山西持续暴雪天气进行了分析,发现这次暴雪过程不同于以往:(1)高空极涡稳定,强度较强,极锋位置偏北,沿极涡外围极锋锋区上分裂的短波小槽,与南支槽同相叠置,使得南支槽发展加深,暴雪发生在此期间。(2)地面图上,不仅形成回流形势,而且河套倒槽向北发展旺盛,倒槽前的暖湿空气与东南气流相遇,两支气流耦合加强,与北方冷空气在山西中南部强烈交汇,使得山西中南部出现了暴雪天气,这种回流形势与倒槽同时强烈发展的情况并不多见。(3)深厚的湿层和强烈的水汽辐合为暴雪的产生提供了充足的水汽条件,暴雪中心就位于中低层两条水汽通量轴线交汇的南侧。(4)高层辐散、低层辐合的垂直配置以及暴雪区上空强烈的上升运动和低层露点锋的持续抬升作用,触发中层高不稳定能量的连续释放,是造成连续暴雪的重要机制,而低空、超低空急流的存在,不仅为暴雪提供了水汽来源和热量输送,而且使得重力波不稳定发展,加强了抬升运动。(5)暴雪出现在500hPa正涡度平流中心右前方,暴雪出现12小时后,正涡度平流中心强度迅速增强,对应暴雪出现一个增幅期。

台风倒槽导致河南不同强度降水的对比分析

登陆后减弱的台风系统(低压、倒槽)经常为内陆省份河南带来不同强度的降水。为了更好地预判台风倒槽降水的强度,寻找台风倒槽暴雨预报关注点,对19802017年间河南省台风倒槽降水样本进行分析,发现区域暴雨出现的概率达78%,冷空气影响与否和动力条件强弱是决定台风倒槽降水强度的关键因素。选择登陆点相似、陆上移动路径相似但降水强度差异较大的1312号台风“潭美”(区域暴雨)和0604号台风“碧利斯”(一般性降水)作为两类降水的典型个例,进行对比分析。结果表明:“碧利斯”倒槽降水产生在暖区,无冷空气参与。而“潭美”倒槽降水,850 hPa以下有冷空气影响,湿位涡斜压项对降水的贡献大于正压项的。“潭美”过程的水汽、垂直上升速度、斜压性远比“碧利斯”的强。低层冷空气入侵为“潭美”降水增强起到以下几个作用:1)加强了大气的斜压性,使台风低压系统通过获取斜压能量得以维持并发展;2)加强了低层风场的辐合;3)南下冷空气与台风系统相遇(冷暖交汇)导致锋生,伴随锋生出现的次级环流上升支进一步促进了垂直上升运动;4)冷暖空气对峙形成近于垂直地面的θse陡立锋区,引起倾斜涡度发展,进一步加强低层辐合和上升运动,将水汽源源不断送往高层,使降水增强。因此,冷空气对台风倒槽暴雨的形成至关重要。在有较强水汽输送的前提下,中高纬有无冷空气南下与台风低压系统共同作用,是判断能否形成区域性暴雨较为关键的因素。而冷空气作用导致的斜压性增强及动力条件改善,是河南台风倒槽暴雨形成的重要机制。

一次暴雨过程受不同系统影响的动力热力场结构特征

本文使用常规观测资料、卫星云图、自动气象站降水量以及0.25°×0.25°的NCEP/NCAR再分析资料,对出现在东北地区北部受不同系统影响的连续2d暴雨过程的热力和动力场结构特征展开研究。结果表明:24日为暖锋锋生暴雨,暴雨范围大;25日为台风暴雨,暴雨出现在台风移动路径上,为狭长带状。暴雨是由MCS活动造成的,每次短时强降水均与TBB低值中心相对应,台风倒槽内的MCS强度比暖锋云系内的MCS弱,但是降水强度却更大。台风安比携带大量暖湿空气,其东侧的低空急流向北输送热量和水汽,水汽辐合集中在边界层内,台风暴雨的水汽辐合强度比暖锋暴雨更强烈,所造成的雨强更大。暖锋暴雨期间,小兴安岭迎风坡地形的辐合抬升作用明显;高层强辐散及地形辐合抬升作用对暴雨有较大贡献。台风暴雨期间,低空辐合,特别是水汽辐合作用对暴雨有较大贡献;辐合区位于台风倒槽附近,倒槽表现为冷锋性质。