Inter‐decadal variation of the summer precipitation in East China and its association with decreasing Asian summer monsoon. <b>Part I: Observed evidences</b>

TLDR

In the past two decades, North and Northeast China have experienced severe droughts, whereas the Yangtze River basin and South China have seen more intense heavy rainfall and flooding. The study examined long‑term summer precipitation and monsoon circulation using 740 surface stations (1951‑2004) and 123‑year records (1880‑2002), identifying abrupt climate change points in 1978 and 1992 during a southward shift of precipitation zones. The analysis reveals an ~80‑year oscillation as the dominant driver of inter‑decadal summer precipitation variability, with additional 12‑ and 30‑40‑year modes, a shift from a +−+ to a dipole meridional pattern, and concurrent weakening of the East Asian summer monsoon and tropical easterly jet, linked to high‑latitude cooling and low‑latitude warming. © 2007 Royal Meteorological Society.

Abstract

Abstract In recent two decades, North and Northeast China have suffered from severe and persistent droughts while the Yangtze River basin and South China have undergone much more significant heavy rainfall/floods events. This long‐term change in the summer precipitation and associated large‐scale monsoon circulation features have been examined by using the new dataset of 740 surface stations for recent 54 years (1951–2004) and about 123‐yr (1880–2002) records of precipitation in East China. The following new findings have been highlighted: (1) One dominating mode of the inter‐decadal variability of the summer precipitation in China is the near‐80‐yr oscillation. Other modes of 12‐yr and 30–40‐yr oscillations also play an important role in affecting regional inter‐decadal variability. (2) In recent 54 years, the spatial pattern of the inter‐decadal variability of summer precipitation in China is mainly structured with two meridional modes: the dipole pattern and the positive‐negative‐positive (“+ − + ” pattern). In this period, a regime transition of meridional precipitation mode from “+ − + ” pattern to dipole pattern has been completed. In the process of southward movement of much precipitation zone, two abrupt climate changing points that occurred in 1978 and 1992, respectively, were identified. (3) Accompanying the afore‐described precipitation changes, the East Asian summer monsoon have experienced significant weakening, with northward moisture transport and convergence by the East Asian summer monsoon greatly weakened, thus leading to much deficient moisture supply for precipitation in North China. (4) The significant weakening of the component of the tropical upper‐level easterly jet (TEJ) has made a dominating contribution to the weakening of the Asian summer monsoon system. The cooling in the high troposphere at mid‐ and high latitudes and the possible warming at low latitude in the Asian region is likely to be responsible for the inter‐decadal weakening of the TEJ. Copyright © 2007 Royal Meteorological Society