扰动变量在强对流天气分析和模式评估中的应用——以苏北里下河地区引发龙卷的扰动系统为例

2016年6月23日14:00—15:00时,江苏省盐城市阜宁县发生了EF-4级有记录以来的强龙卷风过程,造成了当地30 km长,1.7 km宽的严重气象灾害。受局地环境影响,邻近地区在近50年中发生了大于10人次死亡事件的龙卷风11次,其中6次发生于1979年以后。文章首先是:(1)把6次事件日的再分析变量场分解成瞬时气候和扰动两个部分,发现6次事件都与近地面层出现的负高度扰动轴线和扰动冷暖气团的对峙有关,龙卷发生在暖气团一侧;(2)用模式初始场分解的扰动变量和扰动物理量评估欧美模式对产生阜宁龙卷扰动系统的预报能力。后者的结果也发现,当日14时925 hPa高度扰动槽和850 hPa扰动风辐合线作为环境扰动系统,以及湿涡度扰动和湿散度扰动等环境扰动指标量能够突出地表达有利于龙卷风发生的环境条件。欧洲全球模式能够提前42 h稳定预报出后来扰动槽和环境扰动指标量的位置,美国全球模式也可以提前18 h预报出这样的扰动特征。这些扰动变量和扰动指标量能够快速地帮助预报员判断有可能发生强对流天气的大致时空区域和特征。     

梅雨期龙卷环境条件与典型龙卷对流风暴结构特征分析

利用逐日4次1°×1°FNL/NCEP分析资料及多普勒天气雷达、地面自动气象站等观测资料,在对近十年江苏梅雨期龙卷天气的环境特征进行合成分析并提炼对流参数特征值后,着重对2013年7月7日发生在安徽天长至江苏高邮一带导致龙卷的对流风暴的形成和结构特征演变进行了分析。结果表明:江淮梅雨期间,地面中尺度气旋的右侧附近(100 km)、对流层低层中尺度低涡右下方约200~300km处和低空急流左后侧之间区域是龙卷易发区;梅雨期大气环流背景为龙卷的发生提供了对流层低层充沛的水汽和有利的不稳定层结与动力条件,低层气旋性涡度在龙卷发生前强烈发展,边界层内强的垂直风切变促进了龙卷风暴内气旋性涡度的迅速增强,而对流层低层辐合的增强将有利于初始对流的触发;但梅雨期龙卷对对流不稳定能量蓄积条件要求低于冰雹和雷暴大风;龙卷对流参数特征值及其与气候平均值的差异性为龙卷天气的短期预报提供了参考依据。引发2013年7月7日龙卷的对流风暴起源于地面辐合线附近,地面辐合及中尺度锋区的增强有利于对流风暴的快速发展,此次系列龙卷是由一个生命史较长的超级单体风暴产生,该对流风暴具有典型超级单体的回波特征,风暴内的中气旋维持2h之久,中气旋相关参数的演变对龙卷的临近预警有较高的参考价值,当中气旋底高较低且中气旋切变值明显增强时,发生龙卷天气的可能性较大。     

Spatial and Temporal Characteristics of Tornado Path Direction*

Common perception is that tornadoes travel in paths from the southwest quadrant of directions toward the northeast. This study examines path directions for 6,194 tornadoes that occurred in the eastern two‐thirds of the United States during the twenty‐three‐year period 1980–2002. At the national scale, nearly 70 percent of tornadoes included in the study propagated from the west, west‐southwest, and southwest, with west‐southwest being the highest frequency origin direction. Nevertheless, distinct seasonal and regional variations were found. In central and northern areas of the country, a more westerly or northwesterly path origin prevails during late spring and summer. The midtropospheric flow, convective typology, and synoptic patterns of tornado outbreaks are thought to contribute to the distributions observed in the climatology.     

Structures of Mesocirculations Producing Tornadoes Associated with Tropical Cyclone Frances (1998)

Radar structures of one mesocyclone and one mesocirculation (the term mesocirculation refers to a class of rotating updrafts, which may or may not be as spatially and temporally large as a typical mesocyclone) that developed a total of four tornadoes in association with Tropical Cyclone (TC) Frances 1998 are presented. One tornado developed within an inner rainband near the time of landfall while three of the other tornadoes developed within an outer rainband nearly 24 hours after the landfall. Radar reflectivities of the tornadic circulations averaged upwards of 40 dBZ while Doppler radar wind components directed toward the radar averaged 11 m s−1. It is realized that although TC Frances was a minimal hurricane it spawned several tornadoes (four of which were studied) causing damage exceeding $2 million. These tornadoes were not all located close to the TC center, serving as a caution to forecasters and emergency personnel that the immediate landfalling area is not the only place to watch.While it is difficult to accurately predict the TC tornado location and time of occurrence, the degree of low-level baroclinicity seems to play an important role in tornadogenesis. Another significant finding is that the tornadoes were produced on the inward side of an inner rainband, as well as the inward side of an outer rainband. Consistent with climatology, the forward right quadrant of the TC developed the four tornadoes studied here.The lead author, Professor G. V. Rao died 31 July 2004 at the age of 70. He fell victime to the waves while swimming in Mazatlan, Mexico. This is the last paper he publilshed as lead author.     

CINRAD/SA天气雷达双PRF技术I/Q信号仿真及算法对比验证

新一代天气雷达观测的反射率因子和径向速度为强对流风暴和龙卷的识别预警提供了重要支持,新一代天气雷达实施双偏振升级后其基数据分辨率为1.0°×250m (当前分辨率)。为了测试进一步提高数据分辨率的可行性,杭州和深圳竹子林双偏振雷达将数据分辨率提高到0.5°×62.5m/125m (精细分辨率)开展精细化探测技术试验。该文以2个龙卷天气过程为例,分析了径向速度数据质量,对比分析了两种分辨率下的龙卷风暴回波特征和多个雷达特征量以及TVS识别结果。结果表明：(1)精细分辨率的径向速度(特别是参差PRT模式径向速度)中存在一些非速度模糊奇异值,增加了识别虚假TVS的可能性;(2)精细分辨率雷达回波能更好地描述龙卷风暴特征;(3)精细分辨率的中气旋中心位置与龙卷灾害路径更加一致,Z_max、VIL、SHI和中气旋旋转速度、方位切变等雷达特征量大多大于当前分辨率的,TVS识别次数也多于当前分辨率的。因此,在不考虑径向速度质量的情况下,相比当前分辨率探测,精细分辨率探测更有利于龙卷风暴的识别。

     

2015年5月华南一次龙卷过程观测分析

利用常规观测、珠江三角洲区域自动气象站、广州多普勒天气雷达、深圳机场风廓线雷达及NCEP/NCAR等资料对2015年5月11日下午发生在深圳宝安机场附近的一次龙卷天气过程进行分析。结果表明:这次龙卷发生在500 hPa槽前、850 hPa切变线南侧以及地面冷锋的暖区一侧,上干冷、下暖湿的结构加剧了条件不稳定,环境对流有效位能很大,风垂直切变强,水汽丰富;产生龙卷的回波快速演变为逗点回波,出现钩状回波,龙卷发生在钩状回波内侧的弱回波区附近;与之对应的中气旋旋转速度不断加大,半径减小,并向低层发展。     

美国强天气过程预报进展

介绍了美国近20多年在强天气过程预报方面所取得的进展，并列举了若干有关龙卷风、雷暴大风和冰雹等的预报方法。     

科左后旗甘镇一次龙卷风的天气过程分析

利用卫星云图分析和总结龙卷风相伴随的中小尺度云团的发生、发展过程,对于今后分析和预报强对流天气有可能形成龙卷风有一定的参考价值。     

冷涡背景下辽宁龙卷气候特征和环境条件

为了研究冷涡与辽宁龙卷的关系,揭示冷涡背景下辽宁龙卷发生的特征,利用1951—2020年辽宁省龙卷观测和灾情数据以及欧洲中期天气预报中心ERA5大气再分析资料,收集整理冷涡背景下辽宁龙卷个例,对比冷涡背景下EF2—4级(EF2+)和EF0—1级(EF1?)龙卷物理量参数的差异.结果表明:(1)冷涡背景下辽宁龙卷主要出现...     

云滴数浓度对超级单体龙卷影响的数值模拟研究

为了探讨云滴数浓度对于龙卷发生、发展的影响,利用ARPS（Advanced Regional Prediction System）模式,通过调整云滴数浓度（分别取高3000 cm-3、中1000 cm-3和低100 cm-3）的变化,对2003年7月8日安徽省无为县超级单体龙卷进行理想模拟试验。研究表明:三组试验都模拟出超级单体风暴的特征结构如钩状回波和V型入流缺口;云滴数浓度高的试验中上升气流更强、风暴较先发展且持续时间长,近地面涡度也较其他两组试验更大;从三组试验中找到4个龙卷涡旋,其中云滴数浓度高的试验中有两个,涡旋总持续时间接近30 min,最大近地面风速为46.93 m s-1,最大涡度值为0.42 s-1;高云滴数浓度情况下地面冷池弱,更有利于龙卷产生,并对龙卷的发生、发展有促进作用。