Analysis of the Structure and Dynamics of Monsoon Depression using High Resolution ARW-WRF Model

Abstract

Monsoon depressions (MDs) are the significant synoptic systems over the Indian monsoon region, accounting for a substantial fraction (two-thirds) of the seasonal rainfall and associated hazards. Despite their importance, systematic evaluations of MD structure in high-resolution NWP models remain limited. Here, we simulated ten MD cases using an ARW-WRF model (resolution d01 : 13.5, d02 : 4.5 km nested domains) and evaluated storm-centric composites against ERA5 reanalysis and GPM across 24–60 h lead times. Track and rainfall errors are modest at early lead times and increase gradually with forecast length; track deviations rise slowly with time, while rainfall skill degrades from 24 to 60 hours, with strong overprediction near the storm center, weakening outward with a negative bias on the southern flank. Near-surface (10 m) winds remain nearly unbiased for about two days; uncertainty increases at longer lead times. Despite these errors, the model still reproduces the canonical MD structure, including the low-level cyclonic circulation, cold-to-warm core transition, and 850-hPa wind field.