An Observational Perspective on Precipitation Efficiency of Mesoscale Convective Systems over the Asian Monsoon Region

Abstract. This study investigates the precipitation efficiency (ϵ) of tropical mesoscale convective systems (MCSs) using satellite-based precipitation rates (Ṗ) from GPM IMERG and cloud, ice, and liquid water paths (CWP, IWP, LWP) from the ERA5 reanalysis. We define ϵ as the ratio of Ṗ to CWP, following Li et al. (2022), and phase-partition it using IWP and LWP. We calculate these metrics for a total of 1321 MCSs tracked by the Python FLEXible Object TRacKeR (PyFLEXTRKR) algorithm and focus on southern Asia during monsoon season, given its frequent MCS occurrence. We first look at spatial distributions, analyzing longitudinal and latitudinal trends in MCS versus non-MCS ϵ. MCS ϵ values are 50 % higher than ϵ from non-MCS convection on average and increase more strongly from north to sorth and from west to east. Decompositions of ϵ across different regions of the MCSs indicate that the highest ϵ consistently occurs within the core, followed by the cold and then warm anvils. By scaling ϵ by MCS area and cloud depth, we find that all ϵ metrics increase with area up to an MCS effective diameter of 160 km. This trend is consistent with enhanced ice growth associated with deeper clouds and stronger convective organization in larger MCS, before ϵ decreases again in the largest systems where cloud ice growth has reached its maximum. In contrast, all ϵ metrics increase monotonically with MCS depth, indicating that deeper systems convert cloud condensate into surface precipitation more efficiently without the non-monotonicity observed in the ϵ-area scalings. Finally, ϵ increases rapidly during the first ∼20 % of the MCS lifecycle and decreases more gradually during the remaining decay phase—consistent with our scalings and reflecting enhanced efficiency during periods of system growth, expansion, and deepening.