Improved leading modes of interannual variability of the Asian-Australian monsoon in an AGCM via incorporating a stochastic multicloud model

Abstract

In the present study, we investigated improvements in simulating the two major modes of the Asian-Australian monsoon (AAM) interannual variability by incorporating the stochastic multicloud model (SMCM) into the state-of-the-art ECHAM6.3 atmospheric model. Model results showed that the modified ECHAM6.3, i.e., with the SMCM, improves the simulation of seasonal evolution of anomalous rainfall and low-level circulation. Analysis revealed that the improvement in the simulation of precipitation anomalies of the first mode is associated with the improvement in both enhanced and suppressed convection. In addition, the enhanced easterly vertical shear over the Maritime Continent in the modified ECHAM6.3 contributes to the improvement in an equatorial asymmetry of precipitation anomalies of the first mode. Moreover, the moisture budget analysis demonstrated that the modified ECHAM6.3 improves the seasonal anomalous rainfall of the first mode by ameliorating the vertical mass integral of the moist flux divergence. In addition, the second mode of the AAM interannual variability produced by the modified ECHAM6.3 potentially exerts stronger influence on the ENSO variability compared to the default ECHAM6.3.