Based on FY-2 infrared images and the reanalysis data for six hours of NCEP(1°×1°),the heavy dust storm process occurred on 13 April 2007 in the middle west part of Hexi corridor is analyzed,particularly the cloud head of the descending jet was tracked and the gravitational instability,conditional symmetric instability and conditional instability are diagnosed in detail.

In this paper Monin-Obukhov similarity functions,embeded with local free convection,of surface layer in unstable atmosphere are obtained by using dimensional analysis,in view of turbulent generation and development, based on determinative factors of turbulent transport---turbulent dynamic energy and mixing length.