Evolution Process and Multi-scale Structure of a Polar Low Developed over the Japan Sea on 11∼12 December 1985

[摘要] The evolution process and structure of a polar low (meso-α-scale low in the polar airmass), which developed on 11∼12 December 1985 are studied in Part I of the present study. The fine structure of the polar low is analyzed in Part II.Radar and dense surface observation data indicate the formation of a meso-β-scale low associated by well organized spiral echo bands within the polar low. The horizontal extension and the life time of the meso-β-scale low is∼100km and several hours, respectively. While the polar low moves southeastward with speed of∼50km/hour, the meso-β-scale low moves eastward with speed of∼30km/hour. Strong gust of∼25m/sec and the surface pressure fall of∼2mb/30min are observed when the center of the meso-β-scale low at its mature stage passes over. The relative vorticity and convergence of the surface winds of∼100×10-6 sec-1 and∼-50×10-6 sec-1 are estimated over the central portion of the low. The thick moist neutral layer and the cyclonic flows induced by the polar low are considered to be a favorable environment for the developing of the meso-β-scale low.It is an important conclusion of Part II that the present polar low has a multi-scale structure, i. e., a meso-β-scale vortex in a meso-α-scale polar low.

[学科分类] 大气科学