Subseasonal variability of precipitation in China during boreal winter

Thursday, 18 December 2014
Hai Lin1, Yonghong Yao2 and Qigang Wu2, (1)Environment Canada Dorval, Dorval, QC, Canada, (2)Nanjing University, School of Atmospheric Sciences, Nanjing, China
Using pentad data of the Northern Hemisphere extended winter from 1979 to 2012 that are derived from the daily rainfall of the National Meteorological Information Center of China, subseasonal variability of precipitation in China is analyzed. The two dominant modes of subseasonal precipitation variability are identified with an empirical orthogonal function (EOF) analysis. The first mode (EOF1) is characterized by a monopole in South China, whereas the second mode (EOF2) has a meridional dipole structure with opposite precipitation anomalies over the Yangtze River Basin and the coastal area of South China. These two modes tend to have a phase shift to each other in both space and time, indicating that part of their variability is related to a common process and represents a southward propagating pattern.

The subseasonal variability is decomposed into two components, i.e., that related to the Madden-Julian Oscillation (MJO) and that independent of the MJO. The MJO-related component is obtained using a bivariate linear regression with respect to the MJO index as defined by Wheeler and Hendon. It is found that the MJO contributes to only a small amount (up to 10%) of precipitation variability in South China. EOF1 is associated with the MJO phase 3, corresponding to enhanced equatorial convection in the Indian Ocean and depressed convection in the western Pacific, while EOF2 is related to the MJO phase 5, when the enhanced tropical convection moves to the Maritime continent region. A large part of the subseasonal precipitation variability in China is independent of the MJO. Lagged regression analysis is performed between the leading principal component (PC1) and the MJO-independent component of variability of 500-hPa geopotential height, sea-level pressure and 2-meter air temperature. It is found that the subseasonal precipitation variability in China is related to a wave train from the North Atlantic, development of the Siberian high, and cold air outbreak in East Asia.