关键词: 寒潮, 冷平流, 水汽, 诊断

Abstract:

Based on the observation data from automatic weather station, conventional observations, TBB from FY-2E and NCEP reanalysis data, a strong cold wave event which occurred in northern Xinjiang from 22 to 23 April 2014 was analyzed. The emphasis laid on change of temperature advection, water vapor, unstable condition and characteristics of cloud system evolution when temperature dropped sharply and heavy snowfall occurred. The results indicate that the strong cold ridge of the Caspian Sea was coincided with the European Ridge at earlier stage with the north jet stream extending from the polar region to 40°N, which led the polar cold air to move south and the west-Siberia trough to extend and deepen to the south. The European Ridge retreated to southeast that induced the Siberia cold air to move to the same direction in the late period, which resulted in the strong cold wave occurring in northern of Xinjiang. The cold advection in the middle and lower level rapidly preceded that in the upper level and entered the northern Xinjiang, and the north jet stream enhanced cold advection, which resulted in temperature dropping sharply. The sustained water vapor of south Aral Sea converged along the west and southwest airflow, which provided plentiful water for the snowstorm. The structure of lower-level convergence and upper-level divergence and strong ascending stream provided favorable dynamic condition for snowstorm. Snowfall was produced by cold-front. When the snowfall occurred, cloud top brightness temperature ranged from -44 to -32 ℃. The heavier the snowfall, the lower the cloud top brightness temperature was. The evolution of cloud top brightness temperature provided the reference basis for prediction of the snowfall intensity and snowfall area. Through comparing the EC and T639 results and qualitative and quantitative analysis, the numerical prediction model was insensitive to temperature dropping, while the EC model was superior to T639 in forecasting heavy snow area, it had certain guiding meaning on forecast of snowstorm area.

Key words: cold wave , cold advection , water vapory, diagnostic analysis