强沙尘暴天气过程的螺旋度特征分析

利用NCEP/NCAR每日4次全球再分析网格点资料以及常规观测资料,对发生在内蒙古中西部的一次强沙尘暴天气进行了诊断分析。结果表明：在沙尘暴发生区上空,强沙尘暴发生时,螺旋度的绝对值达到最大,这与强沙尘暴发生的时间是基本一致的,且此时螺旋度的垂直分布呈明显的上负下正的形式,而在沙尘暴发生前和减弱时,或者螺旋度的垂直分布值较小,并且没有形成螺旋度明显的上负下正的分布形式;强沙尘暴天气爆发时,沙尘暴发生区上空螺旋度的垂直分布特征在对流层下层为正值区,对应正的垂直速度,而在对流层中上层为负值区,对应负的垂直速度,则低空深厚的上升运动区对应的螺旋度垂直分布形势十分有利于沙尘暴的发展;高低层螺旋度与强沙尘暴的发生、发展在时间上有较好的对应关系,这就说明螺旋度作为一个反映动力参数的物理量,在强沙尘暴预报中有一定的指示意义,且螺旋度的水平分布特征可以反映强对流天气的位置,与天气系统关系密切,故可以将其投入业务使用。

Characteristic Analysis on Helicity of Severe Sandstorm Weather Process

The weather process of a severe sandstorm happened in Northwest China was analyzed by using global reanalysis grid data of NCEP/ NCAR for 4 times a day.As an important physical parameter in analyzing and predicting strong convective weather,the helicity also has good indication in the forecasting of sandstorm.The distribution of helicity over the sandstorm area was negative at higher levels and positive at lower levels,but there is not the phenomenon before or when the sandstorm weakened.The distribution of vertical speed over the sandstorm area was negative at higher levels and positive at lower levels,which is good for the taking place of the sandstorm.There was definite relationship between the evolvement of helicity＇s negative value at higher levels and the occurrence of sandstorm,the horizontal distribution of helicity can represent the position of the convective weather and there is close relationship between helicity and weather system.