Observation- and numerical-analysis-based dynamics of the Uttarkashi cloudburst

Abstract

A Himalayan cloudburst event, which occurred on 3 August 2012 in the Uttarkashi (30.73ﾰ N, 78.45ﾰ E) region of Uttarakhand, India, was analyzed. The near-surface atmospheric variables were analyzed to study the formation, evolution, and triggering mechanisms of this cloudburst. In order to improve upon the understanding provided by the observations, numerical simulations were performed using the Weather Research and Forecasting (WRF) model, configured with a single domain at 18 km resolution. The model was tuned using variation of different parameterizations (convective, microphysical, boundary layer, radiation, and land surface), and different model options (number of vertical levels, and spin-up time), which resulted in a combination of parameters and options that best reproduced the observed diurnal characteristics of the near-surface atmospheric variables. Our study demonstrates the ability of WRF in forecasting precipitation, and resolving synoptic-scale and mesoscale interactions. In order to better understand the cloudburst, we configured WRF with multiply nested two-way-interacting domains (18, 6, 2 km) centered on the location of interest, and simulated the event with the best configuration derived earlier. The results indicate that two mesoscale convective systems originating from Madhya Pradesh and Tibet interacted over Uttarkashi and, under orographic uplifting and in the presence of favorable moisture condition, resulted in this cloudburst event.