Assessment of model time step and domain resolution of WRF model to simulate the lightning over Bihar and Rajasthan, India

The present study aims to understand the role of model Time Step (TS) and domain resolution in order to simulate the lightning event using Weather Research and Forecasting (WRF) model. Two lightning cases over Bihar and Rajasthan have been selected that occurred on 25 June 2020 and 11 July 2021 respectively. The cases were picked with different synoptic conditions during the monsoon season, and both incidents are listed by the India Meteorological Department as the deadliest lightning events. This study consists of 12 experiments based on the model Time Step (50 s, 40 s, 30 s, and 20 s) and model resolutions of nested domains (9 km, 3 km, and 1 km). Examining the model time step is one of the key aspects of numerical simulation since a TS that is too long may lead to model instability and a TS that is too short will need excessive processing power. Model simulated results of the designed experiments reveal the sensitivity and performance of different TS. The model simulated lightning flash count results of 20 s TS shows better spatial agreement with observation; however, Lightning Potential Index (LPI) fails to capture the lightning threat. It might be because the hydrometeors and relative humidity from the 20 s TS model output suggest the absence of vertical extent in the charging zone. After considering LPI and flash count to indicate the lightning threat, the model output for 30 and 40 s TS exhibits higher spatial agreement with observation.