Impact of the Indian Ocean subtropical dipole on the precipitation of east China during winter monsoons

Abstract

A link between the Indian Ocean subtropical dipole (IOSD) of sea surface temperature anomalies (SSTA) and rainfall in east China during winter monsoons is unraveled, and the associated physical mechanism has been identified. A sea-air interaction in the southern Indian Ocean (IO) linked to IOSD changes the internal heating distribution of the atmosphere over south Asia and east Asia, and then a low-frequency wave train of the circum-Pacific pattern (CP) around the Pacific Ocean at 500 hPa during the Northern Hemisphere winter is generated, corresponding to a series of anomalous anticyclone and cyclone circulation at 850 hPa. During boreal winter when a positive (negative) IOSD event occurs, a southwestern (northeastern) wind anomaly appears over southeastern China to the south of an anomalous cyclone (anticyclone) circulation, and such a wind anomaly is associated with a strong ascending (descending) motion. As a result, rainfall anomalies in the south of the Yangtze River and northern China tend to be increased (decreased). The impacts of the IOSD on the China climate during winter are very different from those of ENSO, and the difference of the geographical regions for dry/wet conditions in the winter in China influenced by IOSD and ENSO is significant. Hence the CP wave train related to IOSD is one of the key factors resulting in the rainfall anomalies in east China during winter monsoons. Copyright 2009 by the American Geophysical Union.