Interdecadal Climate Variations Over East Asian-North Pacific Region

By using the monthly precipitation and temperature data at 160 stations in China, the NCEP/NCAR reanalysis data and the HadISST data provided by Met Office Hadley Centre for the period 1950～2003, firstly the interdecadal variation of East China summer/winter rainfall and temperature were analyzed, and basing on this we investigated the interdecadal variation characteristics of atmospheric circulation, sea surface thermal condition and the synoptic-scale transient eddy activities (STEA), accompanying the interdecadal variations of South-Flood-North-Drought over East Asian-North Pacific region, furthermore, discussed the relationship between interdecadal variation of STEA and large-scale general circulation.Some researches reveal the East China summer rainfall is in the interdecadal variation period of South-Flood-North-Drought that North China was severe droughts and Yangtze River was more flooded from the late 1970s, in winter the precipitation in South China is interdecadal increased. In summer the temperature is down over the middle China but up over the North and South China, it seems opposite to the interdecadal variation of East China summer rainfall. In winter the temperature is increased in most region especial the North China. Accompanying the interdecadal variation of South-Flood-North-Drought, the atmospheric circulation and sea surface thermal condition over East Asian-North Pacific area also exist evident interdecadal variation characteristics, the most obvious are:the East-Asian summer monsoon interdecadal weakened, a strong cooling trend is found in the middle and upper troposphere over China, the Western Pacific westerly jet stream (WPJS) abnormally shifted southward, and the South Asian high interdecadally intensified; In winter, the WPJS strengthened, the East Asian trough and the Mongolian High both weakened on the interdecadal time scale.In our research we show that the interdecadal variation characteristics of atmospheric circulation are relate to the middle-latitude STEA variation. In summer the WPJS interdecadally shifted southward since 1970s, the eddy growth rate maximum(σBI) was correspondingly increased, causes the STEA strengthened from the North Pacific to the Siberian Plateau on the interdecadal time scale. However, the associated low-level eddy thermal forcing and eddy moisture forcing do not show significant effect on the interdecadal anomalies of mean air temperature and water vapor in the middle latitude Pacific. In winter, the WPJS is strengthened interdecadally accompanied with the increasing ofσBI underneath the WPJS. This causes intensified STEA on the interdecadal time scale. The strengthened STEA delivers more energy to the westerly wind. Thus the positive feedback reinforces the WPJS anomaly. In winter, the low-level eddy thermal forcing and eddy moisture forcing show evidence of damping effect on the air temperature and water vapor anomalies in the lower troposphere on the interdecadal-scale. The WPJS anomalies has obvious connection toσBI, storm track and barotropic energy conversions (E·▽u) anomalies, and moreover this interrelation in winter is more evident than m summer.