郑州强对流天气成因分析

Analysis of the Forming of Severe Convective Weather in Zhengzhou

对2004年郑州出现的7次强对流天气过程的天气形势、影响系统及稳定度的分析结果表明:华北低涡和NW气流形势下存在着低层升温、高层降温机制,使大气层结趋于不稳定,当测站高低空温差或温度平流差达到一定量值,且近地层存在辐合系统时,易出现强对流; SW气流或高压控制时,大气高温高湿,具有较强不稳定能量,若850 hPa或地面出现辐合系统时,易产生强对流;地面湿度连续数天加大或保持在某一值域,其上空温湿24 h变化呈上趋冷下趋暖或上趋干下趋湿并达到一定量值,预示强对流的发生;700～500 hPa湿度明显减小,24 h温度露点差加大4 ℃以上,或近地层θse≥350K,中低层Δθse≥26 K,θse小值位于700 hPa或500 hPa,其厚度≥2000 m,易出现强雷雨大风; 700 hPa以下t-td≤4.3 ℃,或连续4天850 hPa t-td≤7 ℃、700 hPa t-td≤5 ℃、500 hPa t-td≤9 ℃,PW≥12,可预示短时暴雨的出现.

Through analyzing synoptic situation, influencing system and degree of stability of seven severe convective weather processes in 2004 in Zhengzhou, we indicate that ： In the current situation of North China low vortex and Northwest current there is a mechanism of temperature rising at low layer, temperature falling at high layer, which makes the instability of atmospheric stratification. When the temperature difference between high level and low level or thermal advection difference reaches to a certainty value, there is convergence system near surface, severe convective weather will appear;When Southwest current or high pressure dominates, high temperature and high hu- midity occur, and instability energy increases. If there is convergence system at 850hPa or surface, severe convective weather will appear easily;When the surface humidity increases in continuous days or keeps on a certain value field, and that the temperature and humidity above it vary in 24 hours presents a plumb configuration of getting cold at high level and getting warm at low level or getting dry at high level and getting waterish at low level to a certainty value, it foreshows that severe convective weather will occur ;When the humidity of 700 ～ 500hPa decreases evidently, the difference between temperature and dew-point in 24 hours rises to exceed 4℃ ,or near surface θ3c〉350K, middle and low level Δθ3c≥26K, small θ3c lies in 700hPa or 500hPa and its thickness ≥2000 m, the severe thunder rain and gale will appear easily; When under 700hPa t -td≤4.3℃, or continuous 4 days 850hPa t-td≤7℃, 700 hPa t- td≤5℃, 500hPa t -td≤9℃ and PWΠ≥12, it foreshows that little rainstorm will appear.