ISSN 1002-1027　　CN 11-2952/G2

### A Case Study of a Black Storm at the Northern Foothills of Tianshan Mountains

MA Yu1, WANG Xu1, XIAO Kaiti1, LIU Xiaomei2, TAN Jiang3

• Received:2005-06-13 Online:2006-05-20 Published:2006-05-20

Abstract: Using conventional observational data, autographic records and satellite images, the authors studied a black storm caused by a dry squall line associated with a southern cold front at the northern foothills of Tianshan Mountains in Xinjiang on April 18, 1998. The results show that winds, pressure, temperatures and humidity all have abrupt changes when the black storm passes through meteorological stations, changes associated with the black storm are much stronger than that with dust storms. The dust wall is almost isothermal, with horizontal thickness of about 4-9km. Strong surface winds were mainly caused by rapid intensification of the cold front and the cold advection. Meanwhile, the development of a upper level jet and strong downward transport of momentum by the sinking branch of the upper level jet's secondary circulation are also important for the formation of strong surface winds. The mixed layer is the crucial stratification factor affecting the formation of black storm because it can minimize the energy required to develop the deep dry convection and so is favorable for the formation of black storm in drought region. In this case primary reason that the black storm occurres at the northern foothills of Tianshan Mountain is the formation of deep mixed layer, which is induced by the surface heating for a long time. So the deep dry convection can be developed when the cold front passes and the black storm occurres there.