2009年2月辽宁一次暴雪过程动力条件诊断

应用常规观测资料和NCEP/NCAR再分析资料,对2009年2月12—13日辽宁暴雪过程的主要影响系统（850 hPa切变线）进行动力诊断并研究其演变特征。结果表明：辽宁中西部切变线东南侧、江淮气旋顶部暖锋附近对应强降雪中心;切变线与正涡度区相对应,正涡度带合并、发展并向偏东方向移动,影响切变线的加深发展和东移;850 hPa正涡度中心先于强降雪出现,具有一定预报意义;正涡度带及其中心的生成与发展的动力机制主要受总涡源的影响,涡度变率较涡度更能提前并准确地反映暴雪切变线生成、发展的物理过程;涡度垂直输送和绝对涡度的散度效应对于正变涡的贡献显著,而绝对涡度的散度效应是正涡度变率的主要强迫源;正变涡的减弱主要来自扭转项,抑制了系统的发展。

Diagnosis of dynamical conditions on snowstorm in February of 2009 over Liaoning province

Based on the conventionally observational data and the NCEP/NCAR reanalysis data,the main weather systems（a shear line at 850 hPa）of snowstorm on February 12-13,2009 and their evolution were analyzed.The results show that the strong snowfall center is located in the southeast side of shear line in the middle and western Liaoning province and near warm front of the top of Jianghuai cyclone.A shear line is related to a positive vortex area.The positive vortex belt is integrated and developed and moved to east,which influences the development and movement of shear lines.The positive vortex center at 850 hPa appears in advance of the snowstorm,which is significant for prediction.The dynamical mechanism of the generation and development of positive vortex belt and its center are influenced by the total vortex sources.Compared with vortex,vortex variability could reflect accurately and well ahead the physical process of generation and development of snowstorm shear line.The vertical transportation of vortex and divergence effect of absolute vortex contribute significantly to the positive vortex variability,and the divergence effect of absolute vortex is the primary forcing source of the positive vortex variability.The decreasing positive vortex variability is mainly from twisting factor,which suppresses the development of snow.