沙尘暴热力结构的个例研究

A Case Study on the Thermal Structure of Sandstorms

利用民勤站L波段探空雷达2004年5月23—24日的一次强沙尘暴过程加密探测资料,从气象要素的垂直廓线和能量天气学两个方面,分析了沙尘暴发生发展过程中大气层结及其演变特征。结果表明:沙尘暴过境前,500 hPa以下的高空风速较小,低层800 hPa以下基本为偏东气流,中高层为偏西气流,沙尘暴过境时近地层风速明显加大,700 hPa以下为西北气流,高层为西南气流;相对湿度在沙尘暴过境前,高层明显高于低层,而过境后,整层大气的湿度明显增加,且800 hPa附近出现逆湿现象,沙尘暴过境前后整层大气相对湿度在垂直方向上的变化趋势基本一致。沙尘暴发生前,近地层气温较高,200 hPa附近存在超低温现象,250 hPa附近存在比较厚的下沉逆温层,随着沙尘暴过境,低层的气温显著下降,近地层约800 hPa处出现逆温层,而250 hPa处的逆温层逐渐减弱;地面气象要素的变化为:沙尘暴过境之前,地面气压比较低,温度较高,风速也比较小,而沙尘暴一到,顿时气压升高,风速猛增,温度下降;沙尘暴过境前,500 hPa以下处于对流不稳定,过境期间饱和能差逐渐减小,不稳定能量由高层向低层传递,单站的垂直运动发展加剧;沙尘天气结束后,整层大气的结构基本稳定,不稳定能量衰竭,饱和能差进一步减小,整层大气湿度有了较大的增加。

In order to study the atmospheric stratification characteristics and the thermal structure of sandstorms, we performed an intensive observation during the passage of strong sandstorms process in Minqin,Gansu province from 23rd to 24th May 2004,by using the L-band radar sounding. The vertical profiles of meteorological elements and energy synoptic meteorology are used to analyze the characteristics of the atmospheric stratification and the evolutional characteristies of the atmosphere during the development process of the sandstrom. The results are as follows ： Before the sandstrom arrived at Minqin, the wind speed below 500 hPa was small,there was the easterly flow below the 800 hPa level and the westerly flow at the middle-upper level. When the sandstrom passed through Minqin,the wind speed increased apparently in the surface layer, below the 700 hPa level was the northwesterly flow and the southwesterly flow in the upper atmosphere. The high-layer relative humidity was higher than that of the low-layer atmosphere before the passage of the strom, however after the passage, the relative humidity increased obviously,and there was a humidity inversion phenomenon near 800 hPa. Around the passage the entire atmosphere had a vertically consistent trend of humidity. The surface temperature was higher before the passage, there was a super low temperature phenomenon near 200 hPa, and a thicker subsid-ence inversion layer near 250 hPa, along with the passage of the sandstorm, the temperature in the lower level dropped markedly,the temperature inversion layer near 250 hPa gradually weakened and another temperature inversion layer occurred near 800 hPa. Before the passage, there were low pressure, high temperature and weak wind near the ground surface, when the storm arrived at Minqin, the pressure surged up, the wind speed rapidly increased, and the temperature dropped. The atmosphere was convectively below 500 hPa before the passage,during the saturation energy deficit reduced gradually ,the unstable energy was transferred from upper layers to low layers, the development of vertical motion was intensified. After the passage, the whole atmosphere was stable, the unstable energy was used up, and the whole atmospheric humidity increased greatly.