Characteristic features of Strong and Weak phases of Indian Summer Monsoon Rainfall over Kerala as observed with a VHF Wind Profiler Radar: A case study for 2020

Abstract

In this thesis, the characteristic features of strong and weak phases of Indian Summer Monsoon (ISM) for the year 2020 is explored based on Radar observations and Reanalysis data at the Gateway of ISM. During the peak monsoon months of July and August, strong-weak phases are defined as times in which "the normalized anomaly of rainfall over the Core Monsoon Zone (CMZ) exceeds 1.0 or is less than -1.0 for at least three consecutive days" \cite{Rajeevan2010}. Since the strong-weak events are identified w.r.t the Core Monsoon Zone, we make a comparison of rainfall events over Cochin with that over the CMZ. For the year 2020, we find that when the CMZ experiences the active rainfall events, the Cochin region experiences less/weak rainfall than that during the weak events over Cochin. The atmospheric features like the changes in lower-level jet streams (LLJ), tropical easterly jet streams (TEJ), depth of Westerlies (DoW), moist atmospheric stability, horizontal wind shear, vorticity, moisture flux convergence (MFC) have been examined to bring out the dynamical factors. The analysis was carried out using wind data from Radar, the outgoing longwave radiation (OLR) and also rainfall anomalies. Attempt is also made to bring out the phase relation of Kerala rainfall with that of CMZ.