An analogy-based method for strong convection forecasts in China using GFS forecast data

This paper describes an analogue-based method for producing strong convection forecasts with conventional outputs from numerical models.The method takes advantage of the good performance of numerical models in predicting synoptic-scale weather situations.It calculates the convective parameters as predictors to detect the favorable-occurrence environment of strong convections.Times in the past when the forecast parameters are most similar to those forecast at the current time are identified by searching a large historical numerical dataset.The observed strong convection situations corresponding to those most similar times are then used to form strong convection forecasts for the current time.The method is applied as a postprocess of the NCEP Global Forecast System(GFS)model.The historical dataset in which the analogous situations are sought comprises two years of summer(June–September)GFS 6-to 48-h forecasts.The strong convection forecast is then generated every 6 h over most regions of China,provided the availability of strong convection observations.The results show that the method performs well in predicting strong convections in different regions of China.Through comparison with another postprocessing strong convection forecast method,it is shown that the convective-parameter threshold problem can be solved by employing the analogy method,which considers the local historical conditions of strong convection occurrence.

Comparative Analysis of Strong Convection Process of Convective Cold Cloud and Convective Warm Cloud Type

On the night of April 20, 2017, there was a heavy rain in Longyan City, accompanied by strong convective weather such as strong lightning, short-term heavy precipitation, and 6 - 8 thunderstorms. The three-hour rain intensity and the six-hour rain intensity of Shanghang Tongxian Township and Nanyang Town were once in a century. Through the use of radar, radar wind profile and lightning locator data, the process can be divided into two phases: The first stage is the strong precipitation stage of Changting Datong Town during the 20 - 22 periods on the 20th. The process is accompanied by short-term heavy precipitation (59.7 mm/h), strong lightning activity, and 6 - 8 thunderstorm gales. It is a convective cold cloud dominated precipitation. The second stage is the strong precipitation stage of Shanghang Tongxian Township on the 21st, 02 - 04, and the short-term strong precipitation intensity reaches 75.7 mm/h, but the lightning and wind activity are weak, which is the convective warm cloud-oriented precipitation. There are significant differences in the strong convective weather between the two phases in the same background. The analysis shows that the strong echo of the first stage radar (above 60 dBz) is block-shaped southward, the speed of movement is fast, the height of the echo top is high, and the rear nascent monomer forms a train effect. In the second stage, the southwest-northeast-oriented convective zone moves to the northeast direction, forming the train effect of the echo zone. The center intensity is above 50 dBz, the echo top height is low, and the precipitation center moves slowly. This caused a large amount of accumulated rainfall. In this paper, the radar data is used to analyze the heavy rainfall process on the west coast of the straits, which has certain indication significance for the predictability of strong convective weather.

Two-dimensional simulation of frost formation on the NACA0012 airfoil under strong convection by using the p-VOF method

A newly developed frosting simulation method,p-VOF method,is applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection.The p-VOF method is a pseudo VOF method of the multiphase flow simulation with phase change.By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software,the efficiency and robustness of calculation are greatly improved.This progress makes it possible to predict a long-time frost formation.The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties.The simulation result shows that the average thickness of the frost layer increases,and the frost bulges and flow separation appear earlier,when the airfoil surface temperature decreases or the air humidity increases.The frost bulges and flow separation appear earlier,when the air velocity is faster,the growth rate of the frost layer at the early stage is greater,but the final frost layer is thinner.

Analysis of a Large-Scale Strong Convective Weather under a Weak Water Vapor Condition in Shanxi, China in Spring

This article uses NCEP 1° × 1° grid point reanalysis data, conventional meteorological observation data, FY2G satellite TBB data, radar combined reflectivity data, ground-encrypted automatic station observation data, etc., through the synoptic diagnostic analysis method for a comprehensive analysis of a large-scale underreporting of a strong convective weather process under weak water vapor conditions on the 13th April 2017. The results show that the severe convective weather process is affected by the short-wave disturbance in the northwesterly airflow, triggered by the uplift of the westerly trough, the mid-low shear line and the mesoscale front of the boundary layer in the dry northwest. The jet stream is also an important system for the development of this strong convective weather. In the case of weak water vapor and energy conditions, if there is strong dynamic uplift, vertical wind shear and large temperature differences, strong convection can still occur;the convection occurrence area corresponds to the high potential vorticity abnormal area. The movement speed and direction of the cloud cluster are also consistent with the movement of the high potential vorticity anomaly area;the potential vorticity anomaly will cause the cyclonic circulation to increase, and the upward movement will also increase, which is conducive to the development of strong convective weather. According to the position of the dew point front in the β mesoscale, the ground cold pool corresponds to the small value area of the convective cloud cluster TBB. The front of the cold pool is accompanied by a mesoscale ground convergence line, and the uplift is strengthened, which is conducive to the development and forward movement of thunderstorms;the outflow of the cold pool is guided by 700 hPa. When the wind direction is the same, the movement speed will increase, and the stronger the outflow, the faster the movement speed.

一次冷涡背景下次天气尺度系统对强对流环境场的影响

在同一东北冷涡背景下,2016年6月12—13日山西境内连续2 d出现强对流天气,12日为分散性对流而13日为大范围强对流。基于多源资料通过对比探讨次天气尺度系统及其演变对风暴环境进而对风暴结构的影响,得出以下结论:(1)两日风暴强度和风暴结构差异显著。6月12日对流孤立分散且回波强度小于55 dBZ,而13日准线性风暴发展成尺度较大的弓形回波引发大范围强对流天气,回波强度达60 dBZ。(2)此次过程的关键影响系统为冷涡背景下的次天气尺度低涡。12日次天气尺度低压扰动开始出现,距离远而未影响山西;13日低压扰动东移发展为次天气尺度切断低涡,低涡相关的地面冷锋及850 hPa切变线触发山西上游对流。(3)12日低层水汽含量低,0~3 km垂直风切变弱,13日低涡前偏南水汽输送使低层显著增湿,叠加中层干冷空气形成不稳定层结,受低涡影响0~3 km风垂直切变增强至5.0×10-3s-1,冷锋触发的对流风暴在上述环境下强烈发展并产生阵风锋,阵风锋组织风暴形成飑线,冷池与0~3 km风切变相互作用使飑线维持。(4)13日有利于飑线发展的环境要素与东北冷涡西侧的次天气尺度切断低涡系统密切相关,次天气尺度低涡是飑线形成发展的关键系统。

冰雹云和雷雨云单体VIL演变特征对比分析

以3D—Barnes方案插值的兰州站新一代天气雷达反射率因子等高平面资料，用垂直累积液态含水量（Vertically Integrated Liquid Water Content，简称：VIL）的理论模式计算单体VIL、用MAX函数逐次提取最大VIL（简称：VILmax），采用统计和分段函数处理技术，对20042005年5～8月青藏高原东北侧的32个强对流云单体VILmax的演变特征及其在冰雹云识别中的应用进行了分析。结果表明：（1）强对流云单体VILmax在演变过程中均是先增加，后减少，在时间序列曲线中表现为单峰型特征，其中冰雹云单体VILmax存在“爆发式增长及突然降低”现象，这是区别雷雨云单体的一个重要特征；（2）冰雹云单体首次降雹前4个资料时间间隔内VILmax将出现两次“爆发式增长”现象，第一次爆发式增长时不会降雹，维持1～2个资料时间间隔后第二次出现时开始降雹；同一单体再次降雹前没有第一次“爆发式增长”现象，出现“突然降低”现象时降雹均停止；（3）VILmax变化率（简称：GVILmax）的“正（负）峰”现象与冰雹云单体VILmax的“爆发式增长及突然降低”现象对应的时间完全吻合，利用GVILmax建立的冰雹云识别流程在实际业务中具有较高的使用价值。

青藏高原东部地形对四川盆地东北部一次暴雨过程的影响

针对2021年8月8日发生在四川盆地东北部的一次暴雨,利用地面观测和再分析资料,结合WRF(Weather Research and Forecasting)敏感性数值试验,研究了青藏高原东部地形对本次暴雨过程的影响和机理.结果表明,暴雨发生期间四川盆地主要受500 hPa高压脊影响,青藏高原东南侧绕流形成的西南气流向暴雨区输送暖湿空气,并在盆地形成低涡.高低空系统的耦合使得气流辐合抬升,为暴雨发生提供了良好条件.当青藏高原东部地形高度降低以后,地形对气流的阻挡作用减弱,原先高原东南侧绕流产生的西南气流减弱变为偏西气流.同时,高原东北侧的西北气流加强并南下,进一步减弱四川盆地的南风分量和水汽输送,最终导致水汽在四川盆地东南侧聚集和暴雨落区的南移.

安徽省强对流天气灾害的时空分布特征研究

文章基于1984—2009年安徽省75个县(市)强对流天气灾害的出现次数和灾情情况等资料,以受灾人数、死亡人数、受伤人数、倒塌房屋、损伤房屋、农作物受灾面积、电力倒杆、直接经济损伤、农业经济损失等9个灾情要素,通过线性组合法构建了强对流天气灾害的综合灾损指数,并依据灾损指数确定了强对流灾害的危害程度,分为一般、较重、严重、特重4个等级。结果表明:1984—2009年安徽地区的强对流天气灾害的年出现次数和年灾损指数总体呈线性上升趋势,较重、严重、特重等级灾害表现出增长趋势;安徽省强对流天气灾害频发的月份是6—7月,夏季是灾害最频发的季节;皖北地区的灵璧县、砀山县、萧县是强对流天气灾害最严重的地区。该研究可为安徽省的强对流天气防灾减灾工作提供参考。

基于X波段雷达组网的强对流识别

冰雹、暴雨等强对流天气对人类活动的危害巨大,但由于其发展迅速、结构复杂,对其进行自动识别非常困难。基于成都航空港、龙泉,资阳地区3部X波段雷达构成的雷达组网平台,利用雷达组网的高时空分辨率的体扫数据,在传统的U-Net网络基础上进行改进,提出一种基于U-Net语义分割网络的强对流天气识别模型。选取雷达组网中0.5°、2°、3.5°、5°、6.5°、8°和9°共7层仰角基数据中的径向速度和反射率数据,进行配准、归一化等预处理后形成模型训练所需的数据集。经实验验证,训练后得到的模型对强对流识别的结果比较好。

基于GA‑RF的强对流天气下动态容量评估

容量评估是优化配置管制席位和空域规划的重要依据,为寻找天气特征与运行容量之间的动态关系,提出了基于遗传算法优化随机森林(GA‑RF)的强对流天气下动态容量评估模型。首先,根据不同天气影响量化方法提取空域容量影响指标;然后,采用随机森林特征重要性排序法进行特征选择与降维;最后,构建基于GA‑RF的强对流天气下动态容量评估模型。以北京05扇区为例进行验证,验证结果表明,该模型可在复杂的强对流天气下获取较高的容量评估精度。

A New Algorithm of Rain Type Classification for GPM Dual-Frequency Precipitation Radar in Summer Tibetan Plateau

In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar(DPR) suitable over the Tibetan Plateau(TP) was proposed by analyzing Global Precipitation Measurement(GPM) DPR Level-2 data in summer from 2014 to 2020. It was found that the DPR rain type classification algorithm(simply called DPR algorithm) has mis-identification problems in two aspects in summer TP. In the new algorithm of rain type classification in summer TP,four rain types are classified by using new thresholds, such as the maximum reflectivity factor, the difference between the maximum reflectivity factor and the background maximum reflectivity factor, and the echo top height. In the threshold of the maximum reflectivity factors, 30 d BZ and 18 d BZ are both thresholds to separate strong convective precipitation, weak convective precipitation and weak precipitation. The results illustrate obvious differences of radar reflectivity factor and vertical velocity among the three rain types in summer TP, such as the reflectivity factor of most strong convective precipitation distributes from 15 d BZ to near 35 d BZ from 4 km to 13 km, and increases almost linearly with the decrease in height. For most weak convective precipitation, the reflectivity factor distributes from 15 d BZ to 28 d BZ with the height from 4 km to 9 km. For weak precipitation, the reflectivity factor mainly distributes in range of 15–25 d BZ with height within 4–10 km. It is also shows that weak precipitation is the dominant rain type in summer TP, accounting for 40%–80%,followed by weak convective precipitation(25%–40%), and strong convective precipitation has the least proportion(less than 30%).

ERA5资料在蓟州复杂地形下的检验与应用

以复杂地形的天津蓟州为例,通过对比距离蓟州最近的大兴探空站资料与欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts, ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料的差异,对基于ERA5资料生成的强对流指数在蓟州的适用性进行检验和评估。结果表明:(1)ERA5资料与大兴探空站探测的位势高度、气温和风速在对流层高度吻合,说明ERA5资料能够描述蓟州高空气象条件,且对低空的表现能力比高空准确,各要素中大气湿度的表现相对较差;(2)基于ERA5生成的对流指数中,与强对流天气密切相关的对流有效位能(convective available potential energy, CAPE)、K指数、沙瓦特指数(Showalter index, SI)和大气可降水量(precipitable water, PW)与大兴探空站对应参数的相关系数分别达到0.66、0.90、0.93和0.99,表明利用ERA5构建的对流指数能够揭示大气不稳定层结条件;(3)ERA5对流指数变化与蓟州降水过程相对应,ERA5能够反映天气的变化和发展,为强对流潜势分析提供参考。

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。

2022年“4.11”宜宾地区强降雨、强对流天气分析

利用常规观测资料和卫星资料,从大尺度环流形势、热力和不稳定条件等方面,分析了2022年4月11—12日宜宾市南溪区一次强降雨、强对流天气。结果表明:此次强降雨、强对流天气是在低空急流和低层切变线等诸多有利条件配合下,由槽后强西北气流引导冷空气向南爆发造成的典型横槽转竖型的天气过程。上干下湿的不稳定层结和西南气流输送的不稳定能量为强对流的发生提供了所需的能量条件。卫星云图和雷达回波的演变对此次强降雨、强对流(特别是冰雹云团)的发生有一定指示作用。

关中地区持续性强对流天气成因分析及对农业的影响

为探讨关中地区罕见持续性强对流天气的成因和发生机理,客观分析此次过程对农业的影响情况。利用中国新一代全球大气/陆面再分析产品,常规高空、地面观测以及人工观测冰雹等资料,对2021年7月一次罕见持续性强天气的天气形势、水汽通量散度、假相当位温和环境参量以及影响农业生产的气象干旱指数、风雹对经济林果撞击深度等进行定量化客观分析。结果表明:此次关中地区持续性强对流天气受大气长波调整影响,前期以高空冷平流强迫类配置为主,后期属低层暖平流强迫类;低层偏东气流输送、副高外围西南暖湿气流、明显的水汽辐合和假相当位温密集区扩大造成显著的位势不稳定,是强对流天气发生的有利水汽和热力条件。较大对流有效位能、不稳定层结、垂直风切变增加和适当特殊层高度是强对流天气发生的有利潜势。强对流天气发生为旱情缓解和有效改善土壤墒情做出了积极贡献,但局地强降水和大风冰雹天气导致关中部分农作物倒伏,农田出现积水或土壤过湿现象,不利于玉米、猕猴桃等浅根系作物根部呼吸和养分输送,影响植株正常生长。关中地区多种经济林果出现0.07~0.32 cm的撞击深度,并出现脱落受损现象。研究结果为进一步加强农业气象服务和防灾减灾提供可靠依据。

四川宜宾一次暴雨天气过程分析

利用常规观测资料、卫星资料,从大尺度环流形势、热力和不稳定条件等方面,诊断分析了2021年9月3日宜宾市一次暴雨天气过程。结果表明:此次暴雨是在中高纬两槽一脊环流背景和副高稳定少动的环流形势下,由高原低槽东移、冷空气南下入侵、低空急流和低层切变线等诸多条件共同导致的一次天气过程,其中偏南暖湿气流输送的不稳定能量为暴雨的发生提供了所需的能量条件。此次降雨活动,高度场的预报与实况较为一致,预报效果较好。

川西高原一次强对流天气过程的中尺度特征分析

利用常规、非常规观测资料和NCEP1°×1°再分析资料,分析了2016年7月21日川西高原中部甘孜州一次强对流天气的环境条件和中尺度对流特征。结果表明:(1)地面中尺度辐合线是本次强对流天气过程的主要触发系统。过程期间,高原切变线东移伴随中上层干冷空气扩散南下以及低层暖湿气流北上,整个气层形成“上冷下暖”的不稳定结构并有明显的垂直风切变,有利于强对流的发生。(2)卫星云图上可识别出典型的MCS结构,其对流中心强度TBB在-70℃以下,这些TBB≤-70℃的对流中心与强对流天气区域对应较好,对预报具有较好的指示意义。(3)雷达回波强度最大值为60 dBZ,最大回波顶高为16 km,雷达径向速度图上可识别出弱中尺度气旋。大气垂直累积液态含水量最大值超过55 kg·m^(-2),为强降水的发生提供了充沛的水汽条件。

Genetic Analysis of a Strong Convective Weather Process in Guannan County

To provide references for the forecast of strong convective weather process by county-level stations, through synoptic analysis, diagnostic analysis of physical quantities, analysis of satellite cloud pictures and new generation of weather radar data, the main reasons for the formation of strong convective weather process in Guannan County on May 16, 2012 was analysed based on the weather situation and physical quantities. The results show that this strong convective weather process occurred under conditions of inversion layer, upper dry and low-level wet climate, high- level convergence and low-level divergence, and unstable stratification, and surface cold front was the major factor triggering this strong convection. Besides, radar echo played an important role in the short-term impending forecast during the development of the weather. The occurrence of a strong convective weather is related to cold air activity, so we should strengthen the monitoring of cold air activity, so as to improve our waming lev- el and service capability to forecast strong convective weather.

连续强对流天气下重污染扩散概率预报研究

为了更好地掌握重污染在特定天气条件下的扩散规律,提出连续强对流天气下重污染扩散概率预报研究。在连续强对流天气下将污染划分为重度污染等级、中度污染等级和轻度污染等级;依据等级分类结果,分析重污染扩散概率预报具体要素,建立重污染扩散概率预报框架,预测在连续强对流天气下,不同污染等级的扩散概率,由此完成重污染扩散概率预报方法研究。实验结果表明,轻度污染类型变化情况明显比中度、重度污染类型更为显著,重污染扩散概率预报结果与实际变化情况相符,表明所提方法具有较高的预报精度。

2022年那曲市汛期两次强对流天气的对比分析

选取那曲地区气象站点地面和探空观测资料,结合FY-4A卫星、新一代天气雷达等探测数据,采用天气学诊断分析方法,对2022年8月2日和9月1日发生在那曲市色尼区两次伴有雷暴的强对流天气过程进行了对比分析。结果表明:两次强对流天气均是副热带高压在高原地区活动且在高压边缘触发对流所致,地面辐合线是两次对流天气过程的触发机制。雷达回波的强弱变化与对流天气的发展演变对应较好,雷达回波强度图仍是预报高原对流天气的重要参考。对流层垂直切变和整层水汽条件是把握对流天气性质的主要依据,对流云团、云顶亮温、上冲云顶等云图特征对强对流天气发展、强度变化和未来走向的预报具有重要的参考意义。