Inter-annual Variability of Monsoon Low Pressure Systems in Reanalysis and Climate model Simulation

Abstract:

Monsoon Low Pressure Systems (LPS) play an important role in the Indian summer monsoon by bringing rainfall to the interior parts of Indian subcontinent. The detection and tracking of this weakly structured north north-west propagating system in reanalysis products and climate model simulations are challenging compared to the tropical and extra tropical cyclones. A robust method to objectively identify and track the LPS, which mimics the conventional LPS tracking technique, is presented. The algorithm showed its robustness in detecting and tracking LPS in ERA and MERRA reanalysis products. The algorithm fairly well captured inter-annual variability in ERA/MERRA LPSs against observations from Indian Meteorological Department (IMD). An analysis of the LPS in historical CMPI5 model simulation reveal, the models’ skill in simulating a realistic mean monsoon precipitation and its relation to the LPS activity. Further, this inter-model variability in the LPS is found to be linked to the mid-tropospheric stability over the Bay of Bengal region.