Abstract

The present study focuses on identifying the parameters from the Weather Research and Forecasting (WRF) model that strongly influence the prediction of tropical cyclones over the Bay of Bengal (BoB) region. Three global sensitivity analysis (SA) methods, namely the Morris One-at-A-Time (MOAT), Multivariate Adaptive Regression Splines (MARS), and surrogate-based Sobol' are employed to identify the most sensitive parameters out of 24 tunable parameters corresponding to seven parameterization schemes of the WRF model. Ten tropical cyclones across different categories, such as cyclonic storms, severe cyclonic storms, and very severe cyclonic storms over BoB between 2011 and 2018, are selected in this study. The sensitivity scores of 24 parameters are evaluated for eight meteorological variables. The parameter sensitivity results are consistent across three SA methods for all the variables, and 8 out of the 24 parameters contribute 80 %–90 % to the overall sensitivity scores. It is found that the Sobol' method with Gaussian progress regression as a surrogate model can produce reliable sensitivity results when the available samples exceed 200. The parameters with which the model simulations have the least RMSE values when compared with the observations are considered as the optimal parameters. Comparing observations and model simulations with the default and optimal parameters shows that predictions with the optimal set of parameters yield a 16.74 % improvement in the 10 m wind speed, 3.13 % in surface air temperature, 0.73 % in surface air pressure, and 9.18 % in precipitation predictions compared to the default set of parameters.

Highlights

  • The Indian subcontinent is vulnerable to tropical cyclones which develop in the North Indian Ocean (NIO) that consists of the Arabian Sea and the Bay of Bengal (BoB)

  • The present study focuses on identifying the parameters from the Weather Research and Forecasting (WRF) model that strongly influence the prediction of tropical cyclones over the Bay of Bengal (BoB) region

  • The present study evaluated the sensitivity of the eight meteorological variables, namely surface wind speed, surface air temperature, surface air pressure, precipitation, planetary boundary layer height, downward shortwave radiation flux, downward longwave radiation flux, and outgoing longwave radiation flux, to 24 tunable parameters for the simulations of ten tropical 510 cyclones over the BoB region

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Summary

Introduction

The Indian subcontinent is vulnerable to tropical cyclones which develop in the North Indian Ocean (NIO) that consists of the Arabian Sea and the Bay of Bengal (BoB). These cyclones invariably cause widespread destruction to life and property. The number of tropical cyclones that form in the NIO has increased significantly during 20 the past few years, during the satellite era (1981–2014). An extensive study conducted using the past 30 years of data suggests that the severity of extremely severe cyclonic storms (ESCS) over NIO increased by 26%.

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