The role of soil moisture in the inland penetration of Indian monsoon low-pressure systems

Indian monsoon low-pressure systems (LPSs) are important synoptic-scale cyclonic vortices that typically form over the Bay of Bengal, before penetrating into India where they produce copious precipitation. It has long been argued that high antecedent soil moisture supports their inland penetration. However, recent studies have lent greater support for the role of dynamical processes such as moist barotropic instability. As a result, there is an incomplete understanding of the actual role of soil moisture in their inland penetration. In this study, a convection-permitting (3-km horizontal resolution) setup of the Advanced Weather Research and Forecasting (WRF-ARW) model is used to examine the role of soil moisture in the inland penetration of four LPSs, including the well-known case of Gulab-Shaheen during September–October 2021. Soil moisture perturbations are per- formed in such a way that either a dry or wet land surface is maintained around LPSs throughout the simulation. Multiple land surface models (LSMs) are used to test the sensitivity of the results to the choice of an LSM. The results suggest that irrespective of the LSM, the inland penetration of LPSs is not sensitive to soil moisture; although enhancing soil moisture generally increases LPS precipitation when compared with respective control experiments. In contrast, imposed weakening of the magnitude of total sur- face heat fluxes over land limits the intensification of LPSs and disrupts their tracks, suggesting a greater role of total surface heat fluxes than soil moisture in the inland penetration of LPSs. Thus, this work provides a new perspective on the relationship between soil moisture and LPS propagation.