Role of Autoconversion Parameterization in Coupled Climate Model for Simulating Monsoon Subseasonal Oscillations

Abstract: The Indian summer monsoon (ISM) and associated monsoon intraseasonal oscillations (MISOs) influence the billions of people living in the Indian subcontinent. This study explores the role of autoconversion parameterization in microphysical schemes for the simulation of MISO with the coupled climate model, e.g., the Climate Forecast System version 2 (CFSv2), by conducting sensitivity experiments in two resolutions (~100 km and ~38 km). Results reveal that the modified autoconversion parameterization better simulates the active-break spells of the ISM rainfall. The main improvements include the contrasting features of rainfall over land and ocean and the MISO index, representing MISO periodicity. The improvements are qualitatively and quantitatively more significant in the higher-resolution simulations, particularly regarding rainfall spatial patterns over the Indian subcontinent during active spells. The MISO monitoring index in the revised CFSv2 also shows improvement compared to the control run. This study concludes that proper autoconversion parameterization in the coupled climate model can lead to enhanced representation of active/break spells and sub-seasonal variability of ISM.