The results show that the high potential vorticity,dry air from the upper level of troposphere extended downwards and southwards,which increased the vertical component of the vorticity on the steep iso-entropy plane and promoted the rapid development of the low level cyclone,resulted in a low level jet and the intensive convergence in .

Based on the reanalysis data of NCEP 1°×1°,the diagnostic analysis on potential vorticity,dry intrusion and vertical helicity of a sand-dust storm process occurred in the west of Gansu and Inner Mongolia and the south of Mongolia during period from Oct.

An extraordinary ozone enhancement event is observed at Lin-An (30 30°N, 119 75°E) from March 25 to 31 in the spring of 2001, especially on March 29 and 30 The cause of the ozone enhancement is studied utilizing synoptic meteorology diagnosis from conventional weather data and the NCEP data, as well as potential vorticity (PV).