Impacts of Soil Moisture on the MJO in the Maritime Continent

We examine the relationship between soil moisture and precipitation as the Madden-Julian Oscillation (MJO) propagates across the Maritime Continent. Four high-resolution simulations are conducted using the Weather Research and Forecasting (WRF) model for an MJO event in February 2023: control (CTL), dry soil (SM_D, soil moisture reduced to 0 for the initial conditions), soil moisture reduced to 50% for the initial conditions (SM_M ), and soil moisture increased to 0.8 for the initial conditions (SM_H) . The results indicate that in the SM_D simulation, precipitation increased over the islands of the Maritime Continent and decreased over the surrounding waters. This increase in precipitation and its diurnal cycle initially disrupted the MJO propagation across the Maritime Continent. However, this effect was short-lived, as increased precipitation eventually restored soil moisture to normal levels. Similarly, adjusting the soil moisture to 50% yields a comparable effect. In contrast, increasing soil moisture to 0.8 for the initial conditions weakened moisture convergence and reduced precipitation over the MC during the MJO's passage. The implications of these results are discussed.