Abstract: Based on conventional meteorological observational data and NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data,the enhancement mechanism of the low vortex in a snowstorm from February 15 to 17,2015 over the northeast of Liaoning province is analyzed.The results show the enhancement of low vortex at 850 hPa is the most obvious during the snowstorm event.The absolute vorticity advection term is the major forcing source for the positive vorticity tendency in the upper levels,and the divergence term is the main forcing source for the positive vorticity variability in the lower levels.The enhancement of cold advection at 500 hPa forces the development of positive vorticity variability in the upper levels,resulting in the heterogeneous vertical distribution of vorticity,the increasing differential vorticity advection,the enhancement of vertical ascending motion,and the strong convergence in lower levels.The development of low vortex system in the lower levels results in the convergence of dry and cold northwesterly and northeasterly flows and warm and wet southeasterly flows from the north Yellow Sea over the central region of Liaoning province,which strengthens the snowfall.

Key words: Snowstorm, Low vortex, Vorticity variability, Divergence