青藏高原东北侧局地冰雹统计特征及对特殊雹云单体的讨论

以3D-Barnes方案插值的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的VIL,用VIL与单体顶高度之比计算单体的VIL密度(Vertically Integrated Liquid Water Content Density,简称:VILD),采用统计方法对青藏高原东北侧局地冰雹的日变化和大小分布特征以及地面最大冰雹直径(简称:Rmax)与单体在降雹过程中的最大VIL(简称:VILmax)和最大VILD(简称:VILDmax)之间的关系进行了统计。结果表明:(1)青藏高原东北侧局地降雹主要以中冰雹为主(直径在5~20 mm之间),其次是小冰雹(直径<5 mm,现称为霰),出现大冰雹(直径≥20 mm)的概率很小;(2)从冰雹的日变化特征看,青藏高原东北侧局地降雹主要出现在下午到傍晚,期间存在2个降雹高峰时段。第一个主要集中在13:00~18:00,其中以15:00~16:00出现的概率最高,另一个主要集中在20:00~21:00,日内其余时间降雹概率很小,此结论与陈乾1]等研究区域性冰雹发现的午后傍晚双峰型特征基本吻合,但在出现时段上稍有偏早;(3)VILmax和VILDmax从总体趋势上看与Rmax之间均存在正相关关系,但VILD-max比VILmax与Rmax之间的相关性更好;相同大小的冰雹所对应的雹云单体的VILDmax虽然存在一定的差异,但差异不大,一般维持在0.1 g.m-3以内;(4)雷达观测静锥区和单体强回波区倾斜或悬垂回波等是影响VILmax和VILDmax与Rmax之间出现负相关的2个主要因素。

Statistical Character of Local Hail and Discussion About Special Hail Cloud Cell on the Northeast of Tibetan Plateau

Based on constant altitude plane data of reflectivity factor from new generation weather radar which are interpolated with 3D-Barnes scheme,vertically integrated liquid water content(VIL) of hail cloud cell calculated with its theoretical model,vertically integrated liquid water content density(VILD) calculated by the ratio of VIL value to top height of hailcloud cell,the daily variation character,size distribution and the relations between the maximum diameter of hail on the ground(Rmax) and VILmax,as well as VILDmax of hailcloud cell during hail fall on the northeast of Tibetan Plateau are studied with statistic method.Results are as follows:(1)On the northeast part of Tibetan Plateau,hail fall was mainly in middle size hailstones(diameter range: 5-20 mm),and then smaller size hailstones(diameter less than 5 mm),larger hailstones(diameter more than 20 mm) occurred less;(2)Local hail fall occurred mainly in the afternoon and evening,and there are two peak periods which are from 15:00 to 16:00 and from 20:00 to 21:00,and this result is accordant to the former research of Chen qian et al.on the whole but earlier in occurring period;(3)As a whole,there is a positive correlation between Rmax and VILmax or VILDmax,but the correlation between VILDmax and Rmax is better;some difference exists in VILDmax values of hail cloud cells corresponding to the same size hail but it is small and less than 0.1 g.m-3;(4)The cone of silence for radar detecting,strong echo area leaning and echo overhanging of hail cloud cell are major factors which resulted in negative correlation between Rmax and VILmax or VILDmax.