Abstract:

Based on convention observation meteorological data and the ECMWF ERA-Interim 6 hourly reanalysis data with resolution 0.75°×0.75°，the atmospheric circulation， horizontal helicity， uv component field and vertical velocity of three typical regional cold front sandstorms on March 28-29，2010， April 10-11，2006 and April 24，2010 in Hexi Corridor were analyzed. The results showed that：（1）The main factors affecting intensity and range of sandstorms were high altitude cold air intensity， high and low wind speeds， ground low pressure center， variable pressure gradient before and after the cold front and the time of cold front invading Hexi Corridor. （2）The most obvious factors affecting intensity of sandstorm were 700 hPa wind speed and time of cold front invading Hexi Corridor. The greater low wind speed was， the stronger sandstorm was. Strong sandstorm usually occurred from noon to evening. 700 hPa wind speed threshold of general， strong and very strong sandstorms were 18 m·s^-1， 22m·s^-1 and 24 m·s^-1， respectively. （3）The bigger positive （negative） values of high （low） horizontal helicity and the better their coordination from high to low were， the stronger of sandstorm in the downstream was. High and low-level helicity positive （negative） center value threshold of general， strong and very strong sandstorms were 400（-200）m²·s^-2， 800（-1 000）m²·s^-2 and 1 000（-1 000）m²·s^-2. （4）The u， v component field showed that the greater of wind speed down to near the ground was， the stronger the intensity of standstorm was. The u， v component wind speeds threshold of general， strong and very strong sandstorms were 8 m·s^-1， 10 m·s^-1 and 12 m·s^-1. （5）The stronger rising movement below 700 hPa was， the stronger of sandstorm was. The vertical speed center threshold below 700 hPa of general， strong and very strong sandstorms were -0.4 Pa·s^-１， -0.7 Pa·s^-１and -1.4 Pa·s^-１，respectively. （6）The vertical wind field shows that the lower the descending height of ≥15 m·s^-1strong wind was， the stronger the intensity of standstorm was. The downwind altitude of the general， strong and very strong sandstorms were 600 m， 500 m and 50 m， respectively.

Key words: sandstorm, atmospheric circulation, horizontal helicity, u，v component field, vertical velocity