Circulation structures leading to propagating and non-propagating heavy summer rainfall in central North China

Abstract

Using 30 years of hourly rain gauge records and reanalysis data, this paper reveals two types of heavy summer rainfall in central North China (CNC): the lasting mountain (LM) rainfall and the mountain–plain (MP) rainfall, and further explains their formation mechanisms. The evolutions of the rainfall are found to be closely connected to upper-tropospheric temperature anomalies. When upper-tropospheric warm (cold) anomalies dominate North China (the Japan Sea) and stretch down to lower layers, positive (negative) geopotential anomalies, which appear above the warm (cold) anomalies governed by hydrostatic equilibrium, extend from upper to lower troposphere. In the lower layers, evident low-level easterly anomalies form to the south (north) of the positive (negative) geopotential center, controlling the downstream of CNC and making convective systems difficult to progress eastward. Correspondingly, the low-level convergence and strong convection maintain in the west, and the rainfall persists over the mountains constituting the LM process. But when upper-tropospheric cold (warm) anomalies dominate the west (east) of 110°E and stretch down to lower layers, CNC is situated between an upstream trough and a downstream ridge. As the trough-ridge system progresses eastward, the low-level moisture tongue and strong convections in front of the trough move from the mountains to the plains, and the rainfall propagates downstream constituting the MP process. Results in this paper indicate that upper-tropospheric temperature has significant influence on the evolution of rainfall, and pay attention to its characteristics could provide helpful information in the analysis and forecasting of rainfall propagation.