CHARACTERISTICS ANALYSIS ON FREQUENCY AND MOVEMENT OF SOUTHWEST VORTEX INFLUENCING SOUTH CHINA

doi:10.16032/j.issn.1004-4965.2017.02.011

Abstract：Based on statistical analyses,the characteristics of frequency and movement of southwest vortex influencing south China from March to August in 20 years(1991-2010),are studied by using observational data from MICAPS system supplied by CMA and the gridded reanalysis data from ERA-Interim with a horizontal spatial resolution of 1 °× 1 °.The result shows that the frequency of southwest vortex influencing south China is higher in June and July than any other months.The average duration of southwest vortex increases by month,with the shortest in March (48 hours) and the longest in August (105 hours).According to different moving paths,such southwest vortex can be classified into four types:eastward,southeastward,southward and stagnated vortex.Among them,the eastward type counts the most (37) while the southeastward type counts the least(12).Meanwhile,the duration of stagnated type is the shortest(54 hours) and the maintenance of southward type is the longest (86 hours).Comparing different moving paths of southwest vortex and corresponding large scale circulations,it can be concluded that when southwest vortex is moving (stagnated),the troughs and ridges in middle-upper troposphere is (isn't) clearly seen with a stronger (weaker) divergence movement,also warm(cold) advection and wind convergence (divergence) in downstream of the cradle in the lower troposphere,which is(not) favorable to the development and movement of southwest vortex influencing south China.