Assessment of various cumulus parameterization schemes for the simulation of very heavy rainfall event based on optimal ensemble approach

Abstract

In this study, an attempt has been made to investigate one of the recently occurred extreme rainfall events (EREs) viz.; cloudburst over Pithoragarh district (July 1, 2016) of Uttrakhand in the North-West Himalayan (NWH) region using Weather Research and Forecast model (WRF 3.8.1) based on optimal ensemble approach. Four ensemble members, initialized with perturbed initial conditions corresponding to various cumulus parameterization (CP) schemes, have been generated. Accumulated rainfall for 24 h based on 4 ensemble members have been validated against the remotely sensed HE-rain derived from INSAT-3D measurements. For the simulation purpose, WRF model is tuned with variations in various scale not-aware and scale aware CP schemes viz.; Kain-Fritsch (KF), Bettes’ Miller Janjic (BMJ), Arakawa Schubert (AS), Tiedtke, Grell-Freitas (GF), Multi-Scale Kain-Fritsch (MSKF) and new Tiedtke. It is noted from the present analysis that two out of four ensemble members corresponding to KF scheme simulate rainfall close to the observation. In addition, it is also noted that the spread amongst the ensemble members is very large in case of BMJ, AS, MSKF, Tiedtke, GF and new Tiedtke schemes. Considering large bias amongst various ensemble members for each of the CP schemes, it is suggested that the results based on one ensemble member may be regarded spurious. Further, based on the closest match of ensemble mean with the observation and comparison amongst the simulated grid scale and sub grid scale rainfall corresponding to various CP schemes, it is suggested that scale aware MSKF scheme may be utilized for the simulations of EREs over the NWH region.