冀中南一次春季雨雪过程诊断与预报技术分析

Diagnosis and Prediction of a Rain and Snow Process in Spring in Central and Southern of Hebei

利用常规观测资料、自动站资料、雷达及NCEP 1°×1°资料,在诊断2013年4月19日河北省一次回流多相态降水过程成因的基础上,总结了降雪漏报的原因。结果表明:冀中南降水区位于700hPa切变线南侧、700 hPa西南低空急流与850 hPa东北风急流交汇处,暖湿空气在冷垫上爬升和急流的次级环流为降水提供了动力条件,低空急流为降水提供了水汽条件。整层大气可降水量及变化可作为降水预报的重要参考。对比分析雨区和雪区的温度廓线发现:通过温度平流分析温度的垂直分布和演变比单独分析温度特性层高度对于辨别降水相态更为可靠,而雷达风廓线资料可作为识别冷暖平流进而辨别大气温度层结变化的有益补充。本次降水相态预报出现偏差的主要原因是对温度垂直分布和演变判断不够准确。

There was an obvious precipitation process with the typical return flow on 19 April 2013 in Hebei Province,which was ac-companied with snow in the south and rain in the north of Hebei.It was the latest process with rain and snow conversion in the central and south of Hebei Province.Thus,based on the conventional observation data,the automatic meteorological station data,the radar data and the NCEP reanalysis data at 1°×1°spatial resolution,the missing reason of snow was investigated by analyzing the typical return flow precipitation process.The results showed that the precipitation process was mainly affected by the 500 hPa westerly trough, 700 hPa southwesterly wind jet,wind shear and 850 hPa northeasterly wind jet.The precipitation area just located in the south of the 700 hPa shear line and the intersection between the 700 hPa southwesterly wind jet and 850 hPa northeasterly wind jet.The warm moist southwesterly jet climbed on the cold pad of low level northeasterly jet,and its secondary circulation was helpful to the strong upward motion,and the 700 hPa low-level jet offered abundant water vapor for the precipitation,while return flow coming from the northeast of China was relatively dry.The whole atmosphere precipitable water vapor and its variation were considered as important reference in-dex for prediction.The main reason for forecasting deviation of precipitation phase was not accurate enough to determine the vertical distribution and evolution of temperature.It was found by contrast the temperature profiles over rain and snow areas that the lower tem-perature in south and center region dropped continually due to the influence of two cold airs from west and east paths,and then caused a widespread converting from rain to snow,but the temperature in the north region affected by weak warm advection was relatively high, which made precipitation phase to keep liquid all the time.That is to say,,the vertical distribution and evolution of temperature de-rived from temperature advection were more reliable to identify phase than the height of the characteristics temperature layer.The wind profile of radar should be useful supplemented to identify temperature advection and the atmospheric stratification change.