The 10–30‐day oscillation of winter rainfall in southern China and its relationship with circulation patterns in different latitudes

Abstract

AbstractIntraseasonal oscillation (ISO) of winter rainfall in southern China and its relationship with the circulation patterns in different latitudes are investigated using ERA‐Interim reanalysis data and observations. The results show that the rainfall in southern China has obvious ISO characteristics, with a dominant period of 10–30 days. The convergence of the whole layer integral water vapour flux can satisfactorily represent the rainfall rate, and the intraseasonal (10–30‐day filtered) rainfall is converted into a function of different time scale wind and water vapour. At the intraseasonal time scale, rainfall (10–30‐day filtered) is determined by both the 10–30‐day wind and the background (greater than 30 days) moisture. Nine days before the peak day of the intraseasonal rainfall in southern China, there is an abnormal low‐pressure system (10–30‐day filtered) in the polar region (east to Novaya Zemlya), and the low‐pressure system gradually strengthens because of the intraseasonal relative vorticity advection at high levels. The intraseasonal relative vorticity advection guides the intraseasonal geopotential anomaly to move from the high latitude to the low latitude, and the low‐pressure system at the surface also moves southward. There is no intraseasonal precipitation until the low‐pressure system at the surface moves to the region near southern China, because there is little water vapour in northern China and ample water vapour in the south. After the occurrence of precipitation, the vorticity advection from the high latitude no longer affects the strength of the low‐pressure system, but the intraseasonal diabatic heating accompanied by precipitation causes a second drop in pressure from −3 days to −1 day and makes the low‐pressure system strongest here. In addition, the geopotential anomaly (10–30‐day filtered) in low latitudes moves eastward along the southern foothills of the Tibetan plateau, which can guide the low‐pressure system to move southward until it reaches southern China.