Interdecadal Variability Of Indian Ocean Monsoon Circulation And Its Relation To Atmosphere Circulation

The NCEP /NCAR monthly mean reanalyse data and Jones&Parker's data dataset which is a combination of land air temperature anomalies and sea surface temperature anomalies are used to research the interdecadal variability on Indian Ocean and South Asia monsoon circulation in term of running smooth, correlation analysis and EOF method. And their relationships to the atmosphere general circulation of north and south hemispheres are also discussed.A climate shift at middle of 20th century 70's is found in SSTA and 1000hPa,500hPa geopotential height on Indian Ocean, cross-equatorial air flow and South Asia monsoon circulation, and 1000hPa,500hPa geopotential height in south hemisphere's eofl of interdecadal variability. In interdecadal timescale, the first mode of SSTA in summer and winter shows change in phase over Indian Ocean, and the second mode shows change out of phase between middle latitude of southern Indian Ocean and equatorial Indian Ocean. Most of the interdecadal variability in geopotential height on Indian Ocean occurs in southern middle latitude.Contrast to the northern hemisphere, the middle level and low level of southern hemisphere troposphere in interdecadal EOF have similar pattern during austral winter. And the first mode of geopotential height shows latitudinal structure, that is to say high latitude decrease while low-mid latitude increase after year 1976. Study of the westerly index in southern winter suggests a higher index which implies the decrease in exchanges between high and low latitudes after 1976. The second mode shows longitudinal structure, change out of phase is found in middle latitude between different longitudes. 1976's climate shift is detected in EOF2 of northern hemisphere geopotential height, but not in EOF1The cross-equatorial air flow near 45?E in austral winter and near 105?E in boreal winter enhance after 1976's climate shift, suggesting the increase in exchanges between two hemispheres. And south Asia monsoon circulation also becomes strong at the same time, and eastern Asia shows decrease to a larger degree than other summer monsoon region.