High-Frequency Mixed Rossby-Gravity Waves in the Mid-Troposphere Triggered Kerala Floods of 2018

Abstract

Kerala, the South-West coastal state of India, was ravaged by a series of floods during the South-West Monsoon of 2018. The season was marked by severely anomalous rainfall trends, with over 100 mm of departures from the mean daily precipitation in the northern districts of the State. Unlike previous works, this study not only documents the extreme event, but also identifies the tropical dynamics responsible for it. The synoptic disturbances of the tropical Pacific triggered high-frequency Mixed Rossby-Gravity (MRG) waves in the mid-troposphere during Boreal Summer, which meddled with the Monsoon trough, as it propagated westward from the east Equatorial Indian Ocean to the east coast of Africa. Interestingly, these equatorially-trapped waves were found to have teamed up with Madden–Julian Oscillations (MJO) to fuel deep convection in the tropics and caused heavy rainfall over Kerala in 2018.