中国泛华北地区冷季高架对流特征气候统计分析

摘要

本文利用常规地面、高空、区域自动站观测资料、灾害性强对流天气监测记录资料以及NCEP分析数据,对2000-2015年泛华北地区(32.5°～53.5°N、105°～135°E)冷季(除6、7、8月以外)高架对流时空分布特征、锋面环境特征以及不稳定机制进行统计分析.研究发现,泛华北地区冷季高架对流多发生于河南中北部、山东西部及河北中南部.从季节分布来看,2和11月是冷季高架对流发生最多的月份,呈“双峰型”分布特征.冷锋是引发泛华北地区冷季高架对流的主要锋面系统,约占高架对流事件总数的60％.高架对流发生时常伴随有较强的冷垫及锋面逆温,有超过半数的高架对流发生在温差超过6℃的逆温层之上.逆温层顶高多位于850 hPa之上甚至能达到700 hPa.高架对流发生时多伴随有20～30 m· s-1的0～6 km强垂直风切变,这一强斜压特征有利于条件对称不稳定及其导致的高架倾斜对流的发生.经过分类与统计发现,条件对称不稳定和弱条件稳定度或近湿中性大气层结下的锋生强迫引发的较强上升运动是造成华北冷季高架对流的主要不稳定机制.%Conventional surface observation,soundings,comprehensive monitoring data of severe convective weather and NCEP analysis data are used to investigate statistically the spatio-temporal distribution,frontal characteristics and instability mechanisms of cold season (except June,July and August) elevated convections in northern China (32.5°-53.5°N,105°-135°E) during a 16-y period from 2000 to 2015.The events are concentrated in south central Hebei,western Shandong and north central Henan.The annual frequency distribution of elevated convections is bimodal,with a primary peak in February and a secondary peak in November.Cold front is the primary frontal system dominating the events.There exists thick cold surface air and strong temperature inversion when elevated convection occurs and more than half the events are triggered over the inversions with a temperature difference greater than 6℃.In addition,strong vertical wind shear (20-30 m · s-1) is frequently observed which is conductive of symmetric instability.The result further shows that conditional symmetric instability and frontogenetic forcing are the dominant mechanisms generating cold season elevated convections.