The circulation features and sustaining mechanism of a snowstorm event occurred in Henan from February 4 to 7 in2014

Based on conventional observations, surface data from automatic weather station, NCEP 6-hourly reanalysis data with 1°×1° resolution,the blackbody equivalent temperature (TBB) data and Doppler weather radar data, we discuss the circulation features and sustaining mechanism of a snowstorm event occurred in Henan from February 4 to 7 in 2014, and then summarize the three-dimensional spatial structure of influence systems concerned in this event. The results show that the eastward moving trough in the Hetao regions, associated with the southward moving cold air near the ground, is favorable for the cold and warm air to meet in the Huanghe-Huaihe regions, which provides a large-scale background circulation for the occurrence of snowstorm. In addition, the converging of the dry and cold northeast jet and the strong warm and humid southwest jet in the snowstorm zone provides the beneficial water vapor and dynamical conditions for the occurrence of snowstorm. It can be found in the radar echo charts and satellite images that the snowstorm occurred at the place of the maximum gradient of lower than -30℃ TBB in the edge of cold cloud clusters. The movement and intensity changes of radar echoes correspond well with the distribution and intensity of snowstorm. The sustained vapor convergence provides abundant moisture for snowstorm. Strong ascending movement is induced by the uplift of warm and humid air pushed by the southward moving dry an cold air. A significant dry layer in the middle troposphere(600-400 hPa) is formed by two branches of dry and cold downdraft, which result in the formation of saturated layer in the low level and the accumulation of large amounts of energy. Significant frontogenesis emerges in the meeting place of cold and warm air masses. The secondary circulation that is perpendicular to front is formed, and then upward motion is furter strengthened, which plays an important role on the continuance and development of snowstorm.