Interannual variations of OLR in the Maritime Continent in late autumn and early winter and their relationships with precipitation anomalies over the Yunnan-Kweichow Plateau

Based on the monthly mean outgoing long wave radiation (OLR) data from NOAA, the ERA-interim reanalysis from ECMWF, the precipitation data from GPCC and station precipitation data from NMC, by defining a convection intensity index (IOLR) in the Maritime Continent region (MC hereafter), we have investigated the characteristics of convections over MC and the relationships between the convection variations over MC and the precipitation anomalies over the Yunnan-Kweichow Plateau (Y-K Plateau hereafter) in the period of late fall to earlier winter including November, December, and January from 1979 to 2013. It is found that the intensity of convections in MC increases linearly during the past 3 decades. Besides this interdecadal change, the convections in MC change with periodicities of 3-5 years and 8-10 years. When the IOLR is positive (negative), i.e., the convections region are weaker (stronger) in MC, the precipitation is found to be less (more) than normal in the west of the Y-K Plateau and simultaneously more (less) in the east. There are three mechanisms responsible for the precipitation anomaly in the Y-K Plateau. Firstly, the anomalous vertical circulation between MC and the Y-K Plateau connects the downdraft (updraft) over MC and updraft (downdraft) over the plateau. It seems that the terrain may play a role in inducing the precipitation anomaly differences between the southeastern and the northwestern parts of the Y-K Plateau. Secondly, the divergent wind components in both the lower and upper troposphere as a potential vorticity source directly induce the vorticity anomalies in the lower latitudes and in the southern part of China. Thirdly, the anomalous potential vorticity in the tropical region north of MC perturbs the atmosphere, dispersing wave energy from the tropical region northward into the Y-K Plateau, facilitating the maintenance of an anomalous cyclonic circulation there, and inducing rainfall anomalies in the Y-K Plateau. These results are helpful for us to better understand the formation mechanisms of precipitation anomaly over the plateau and for us to find some useful clues to precipitation prediction there in wintertime.