夏季强沙尘暴内部热力动力特征的个例研究

根据对流体在热低压条件下激发强沙尘暴的机理,并应用Rennó和Ingersoll于1996年提出的热机自然对流理论,对2004年7月12日甘肃省酒泉基准站发生的强沙尘暴内部动力热力结构进行了探讨。结果表明:①在沙尘暴发生前的一小时大气底层处于干热状态,垂直方向巨大的温度梯度有利于干对流发展。②激发强沙尘暴的对流体的切向旋转速度和垂直运动速度的大小,很大程度上决定了沙尘暴的强弱。③利用酒泉站探空资料计算出的沙尘暴对流体的最大切向旋转速度为11.4 m·s-1,垂直运动速度为14.0 m·s-1;地面沙尘暴观测系统记录的平均环境风速仅为5.5 m·s-1,瞬间最大风速只9.3 m·s-1。

Case Study of Dynamical and Thermo-dynamical Structure of Serve Dust-storm in Summer

According to the formation mechanism of dust-storm stimulated by serve convection system under hot-low, the thermodynamical structure of a dust-storm which occurred in the Jiuquan area of Gansu Province at 20:00 on July 12, 2004 was analyzed based on the theory of hot-engine natural convection proposed by Renn and Ingersoll in 1996. Findings are as follows: ①The atmospheric bottom layer was dry and heat in an hour before dust-storm occurrence, and there was extreme temperature grade between 200 hPa and 300 hPa, which was advantageous to the development of dry convection. ②The intensity of the dust-storm was closely related to the tangential and vertical velocity of micro-scale and meso-scale convections. Being computed by the sounding data from Jiuquan station the tangential velocity of dust-storm was 11.4 m·s-1 and the vertical velocity was 14 m·s-1; the maximal surrounding velocity recorded by the surface dust-storm observational system was only 9.3 m·s-1, and the average was 5.5 m·s-1.