Weakening of Winter North Atlantic Oscillation Signal in Spring Precipitation over Southern China

摘要

In this study, the relationship between the North Atlantic Oscillation (NAO) in winter (December-February) and the precipitation over southern China (SCP) in the following spring (March-May) was investigated. Results showed an interdecadal change, from strong to weak connection, in their connection. Before the early 1980s, they were highly correlated, with a strong (weak) winter NAO followed by an increased (decreased) spring SCP. However, after the early 1980s, their relationship was weakened significantly. This unstable relationship may be linked to the climatological change of East Asian jet. Before the early 1980s, the wave train along the Asian jet propagated the NAO signal eastward to East Asia and affected local upper-tropospheric atmospheric circulation. A strong NAO in winter led to an anomalous anticyclonic circulation at the south side of 30°N in East Asia in spring, resulting in an increase of SCP. In contrast, after the early 1980s, the wave train pattern along the Asian jet extended eastward due to strengthening of the climatological East Asian jet. Correspondingly, the NAO-related East Asian atmospheric circulations in the upper troposphere shifted eastward, thereby weakening the linkage between the spring SCP and the winter NAO.