Possible Linkage between Arctic Oscillation and Climate over South China Sea during the Boreal Spring
Thursday, 18 December 2014
In this study authors analyzed the possible influences of springtime Arctic Oscillation (AO) on climatic change over South China Sea (SCS), by employing monthly data of precipitation (GPCP), sea surface temperature (ERSSTv3b) and atmospheric circulation from NCEP-NCAR reanalysis data for the period of 1979-2013. Prior to analysis the El Niño-Southern Oscillation (ENSO) signals have been linearly fit to the time series of interests and been subtracted. The first mode of the multi-variable (including SST, precipitation, and horizontal and vertical winds at 850hPa) empirical orthogonal function (MV-EOF) explains 27.8% variance over the domain of 5ºS-25ºN and 105ºE-125ºE. The temporal variations of the first mode co-change tightly with spring AO. Their correlation coefficient is -0.4, being significant at the 0.05 level and their out-of-phase relationship is even more dominant on the interannual time scales. During positive (negative) AO years, an anticyclonic(cyclonic) anomalous circulation is observed over tropical Western Pacific in mid- and lower troposphere. Meanwhile, anomalous southern (northern) winds appear in the SCS area. Corresponding to the circulation anomalies, there are more (less) precipitation in the northern SCS and the neighboring southern China, and the precipitation get drier (wetter) in the central SCS. There are two possible mechanisms linking AO and SCS climate. The first possible way is the wave train along the Asian westerly jet stream. There are two upstream centers, one is located in the Bay of Bengal and Indochina Peninsula, the other located in Arabian Sea. An active wave train enhances the southern winds in SCS. The second possible way seems related to the dipole-structure circulation anomalies over the North Pacific. During positive AO years, an anticyclone and a cyclone circulation appear to the north and south of the stormtracks, respectively. The cyclonic circulation in the western Pacific also modulate SCS climate.