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Unraveling the mechanism of extreme (More than 30 sigma) precipitation during august 2018 and 2019 over Kerala, India

Mukhopadhyay, P and Bechtold, P and Zhu, Y and Krishna, RPM and Kumar, S and Ganai, M and Tirkey, S and Goswami, T and Mahakur, M and Deshpande, M and Prasad, VS and Johny, CJ and Ashimmitra, Ashimmitra and Ashrit, R and Sarkar, A and Sarkar, S and Roy, K and Andrews, E and Kanase, R and Malviya, S and Abhilash, S and Domkawale, M and Pawar, SD and Mamgain, A and Durai, VR and Nanjundiah, RS and Mitra, AK and Rajagopal, EN and Mohapatra, M and Rajeevan, M (2021) Unraveling the mechanism of extreme (More than 30 sigma) precipitation during august 2018 and 2019 over Kerala, India. In: Weather and Forecasting, 36 (4). pp. 1253-1273.

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Official URL: https://doi.org/10.1175/WAF-D-20-0162.1


During August 2018 and 2019 the southern state of India, Kerala, received unprecedented heavy rainfall, which led towidespread flooding.Weaim to characterize the convective nature of these events and the large-scale atmospheric forcing, while exploring their predictability by three state-of-the-art global prediction systems: The National Centers for Environmental Prediction (NCEP)-based IndiaMeteorological Department (IMD) operational Global Forecast System (GFS), the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), and the Unified Model-based NCUM being run at the National Centre for Medium RangeWeather Forecasting (NCMRWF). Satellite, radar, and lightning observations suggest that these rain events were dominated by cumulus congestus and shallow convection with strong zonal flow leading to orographically enhanced rainfall over theGhats mountain range; sporadic deep convection was also present during the 2019 event. A moisture budget analyses using the fifth major global reanalysis produced by ECMWF (ERA5) and forecast output revealed significantly increased moisture convergence below 800 hPa during the main rain events compared to August climatology. The total column-integrated precipitable water tendency, however, is found to be small throughout the month of August, indicating a balance between moisture convergence and drying by precipitation. By applying a Rossby wave filter to the rainfall anomalies it is shown that the large-scale moisture convergence is associated with westward-propagating barotropic Rossby waves over Kerala, leading to increased predictability of these events, especially for 2019. Evaluation of the deterministic and ensemble rainfall predictions revealed systematic rainfall differences over the Ghats mountains and the coastline. The ensemble predictions were more skillful than the deterministic forecasts, as they were able to predict rainfall anomalies (greater than three standard deviations from climatology) beyond day 5 for August 2019 and up to day 3 for 2018. © 2021 American Meteorological Society.

Item Type: Journal Article
Publication: Weather and Forecasting
Publisher: American Meteorological Society
Additional Information: The copyright for this article belongs to American Meteorological Society
Keywords: Budget control; Climatology; Landforms; Mechanical waves; Moisture; Rain, Atmospheric forcing; Deterministic forecasts; European centre for medium-range weather forecasts; Global forecast systems; Lightning observations; Moisture convergence; National centers for environmental predictions; Rainfall prediction, Weather forecasting
Department/Centre: Division of Mechanical Sciences > Divecha Centre for Climate Change
Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited: 16 Nov 2021 11:16
Last Modified: 16 Nov 2021 11:16
URI: http://eprints.iisc.ac.in/id/eprint/69830

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