The large-scale hydrologic cycle and its role in Asian summer monsoon variations induced by Indian Ocean sea surface temperature anomalies

Characteristic variations of the large-scale hydrological cycle (LHC) and their relationships to the variations of atmospheric circulation and sea surface temperature (SST) during northern summer (Jun-Jul-Aug) are studied using the NCAR CCM1 climate model. The principal focus is on the role of the LHC in monsoon system variations and large-scale atmosphere-ocean interactions. The underlying physical couplings are identified by comprehensive analyses of both the control simulation and the anomaly experiments.;Numerical experiments with prescribed SST anomalies in southern Indian Ocean are conducted to test the role of the LHC through its coupling with circulation in influencing the Asian monsoon responses to the remote SST anomalies pertaining to the interannual variations. Significant responses show that the LHC exerts a positive feedback through coupled changes of its component processes similar to those found in the control simulation. The polarity (sign) of the prescribed SST anomaly determines whether the overall monsoon circulation response is enhanced or weakened.;The results from the analyses of both the control simulation and the anomaly experiments are consistent and compare well with observations. These analyses suggest that the positive feedback mechanism highlighted in this study may be partially responsible for some of the variations observed in atmosphere and ocean.;The spatial-temporal variations of the LHC components, viz. evaporation, moisture transport and precipitation in the control simulation are characterized by empirical orthogonal functions. Significant correlations between the dominant modes of the LHC and circulation components on the intraseasonal time scale indicate physically consistent couplings between these components. This set of coupled covariations in space and time suggest a feedback mechanism between hydrological cycle and monsoon circulation.