Comparative analysis of several influencing systems in the process of a large-scale continuous snowstorm

A large-scale rain and snowstorm lasted for 48 h and successively affected Shaanxi, Shanxi, Beijing, Hebei and Liaoning. The snowfall reached 15-30 mm in North China. Surface systems influencing the above rain-snowstorm process are complicated, including the North China occluded front, the Jianghuai cyclone and the northly cold front. By using the quasi-geostrophic theory, the condensation function analysis, vertical cross section analysis, conventional observation data and the GFS 0.5°×0.5° reanalysis data, characteristics and differences in water vapor content, dynamic condition and vertical structure, etc. between the North China occluded front and Jianghuai cyclone and their impacts on snowfall and snowfall efficiency are analyzed. Evolutions and interactions of various surface systems are described as well. The results show that:(1) Considering the snowfall and efficiency, the snowfall amount produced by the North China occluded front was less than that produced by the Jianghuai cyclone. The North China occluded front mainly influenced western North China, where the snow lasted for 24 h. The Jianghuai cyclone mainly affected central and eastern North China, where the snowfall lasted for 30 h. In the first half period of precipitation, the precipitation efficiency of the North China occluded front was 0.76, and that of the Jianghuai cyclone was 0.58; in the later half period, the precipitation efficiency was 1.5 for both systems. (2) Looking at the water vapor condition, the North China occluded front was obviously weaker than that of the Jianghuai cyclone. The water vapor supply for the North China occluded front came from the southwest and large transport occurred on 700 hPa; the water vapor supply for the Jianghuai cyclone came from the southwest and the East China Sea, and large transport were found on the levels of 700 and 850 hPa. The water vapor content and convergence center of the North China occluded front were mainly concentrated near the surface layer, while those of the Jianghuai cyclone were located in 800-600 hPa. (3) Considering the dynamic condition, the North China occluded front was obviously weaker than the Jianghuai cyclone. The vertical differential term was dominant in vorticity advection in the southern part of the North China occluded front, where as the Laplace term played a major role in temperature advection in the northern part. The vertical differential term for vorticity advection and the Laplace term for temperature advection both were important in the Jianghuai cyclone. (4) On the vertical structure, the Jianghuai cyclone was a cold occluded front with the northly cold front undercutting the warm front zone aloft, and its intensity was stronger than that of the North China occluded front. (5) On the evolution and interaction, the northward movement of the Jianghuai cyclone weakened the intensity of the North China occluded front, and the northly cold front behaved like a "cold pad", which uplifted the warm and moist air flow associated with the Jianghuai cyclone.