Rapidly intensified, long duration North Indian Ocean tropical cyclones: Mesoscale downscaling and validation

Abstract

High-resolution (6 km × 6 km) reanalyses (HRR) have been generated using the Advanced Research Weather Research and Forecasting model (WRF-ARW) and three-dimensional variational-Ensemble Kalman Filter (3DEnKF). The six-hourly cyclic downscaling methodology has been used to develop HRR for simulating the life cycle of three rapidly intensified long-life tropical cyclones (TCs) viz. Fani, Ockhi, and Luban over the North Indian Ocean (NIO). The available surface and upper-air observations, radiance data, and scatterometer/radiometer wind data have been assimilated. The simulated maximum surface wind (intensity), minimum sea level pressure (MSLP), and cyclone tracks have been compared to the International Best Track Archive For Climate Stewardship (IBTrACS) dataset. During the maximum intensity stage, the model successfully simulated the maximum surface wind variation and drop of MSLP. The surface winds validated using the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoys observations showed a better correlation at the cyclonic stage and severe cyclonic stage compared to the very severe cyclonic stage. Comparing wind distribution at 850 hPa to the 5th Generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) showed that the analysis successfully captured more intense TC stages. The significant wind structure features in the surface, lower, middle, and upper tropospheric observed by Scatsat-1 and INSAT3D/3DR satellites have been simulated by analysis. The rapid intensifications (RI) of considered TCs were successfully simulated in the analysis. The simulated and the Global Precipitation Measurement (GPM) accumulated rainfall distribution was found to be collocated, especially over heavy rainfall regions.