2011年贵州两次降雪天气过程的多普勒雷达产品特征分析

Doppler radar analyses of twice snowing weather process in 2011 Guizhou

利用常规观测和新一代多普勒天气雷达回波资料对2011年1月l7日至20日贵州省出现的两次降雪天气进行详细的特征分析。结果表明:贵州降雪回波强度一般<30 dBz,中心强度普遍在30～40 dBz之间,反射率因子的分布梯度不大;但降雪过程中夹杂冰粒的时候,回波中心强度能达到50 dBz。降雪回波的顶高一般在7 km以下,其中顶高5-7 km的情况占到60%左右,发展旺盛时回波顶高可达到8 km以上。降雪回波径向速度的等值线比较密集,沿径向梯度变化大。"牛眼"状回波是降雪回波的一个典型特征,"牛眼"状回波正负速度中心值的大小与降雪量存在一定的正比关系。风廓线产品的近地面层风向对于预报降水类型有明显的指示意义,当风廓线产品上近地面1.5 km高度的风向由东偏南转为东偏北时,地面冷平流取代暖平流,雨夹雪向纯雪转换,反之,暖平流取代冷平流,则是纯雪向雨夹雪转换,或者降雪减弱消失。

Using conventional observation and a new generation Doppler radar data on January 17 2011 to 20, ana- lyzed the snowfall weather detailed features appeared twice in Guizhou. The results show that the snowfalls echoes generally are less than 30dbz, and center echoes intensity are between 30 to 40dbz, reflectivity factors distribution gradient is not big; but when the snowfall mingled with ice particles, center echoes intensity are 50dbz. The top highs of echoes of snowfall are under the 7kin, and the top high of 5 -7km accounted for about 60% , the most top high can be achieved 8kin when the echoes are most vigorous. The radial velocity isolines of snow echoes arc inten- sive, along the radial gradient changes are small. ＂Bull ＇ s - eye＂ shape echo is a typical features of snowfall echo, and it plus or minus speed central values with the amount of snow there exist certain proportional relations. Surface layer wind direction of wind profile product to forecast precipitation type has obvious indicator of significance. When the products of wind direction by the east south to north by east on the high of 1.5km, the ground cold advection replaced the warm advection, the rain and snow changed to pure snow, conversely, the warm advection replaced cold advection, and the pure snow changed to rain and snow or the snow weakened and disappeared