Role of MJO in modulating rainfall characteristics observed over India in all seasons utilizing TRMM

Abstract

ABSTRACTThe present study aims to understand the influence of the Madden–Julian oscillation (MJO) on the seasonal and diurnal characteristics (amplitude and phase) of rainfall over the Indian subcontinent (lat. 10°S–38°N, long. 60°–100°E). The study is conducted for the period 1998–2015 and for each Indian season. To accomplish this, the Tropical Rainfall Measuring Mission (TRMM) data set (3B42, version 7) is examined using indices quantifying rainfall frequency percentage and rainfall octet contribution, respectively. The real‐time multivariate (RMM) index developed by Wheeler and Hendon (2004) is used to partition the MJO into active, weak and suppressed phases. The results show that during active and weak phases (suppressed), positive (negative) rainfall anomalies are observed and the frequency of rainfall events is enhanced (lessened) over the most of the geometrically distinct regions. This finding is common to all seasons but is most prominent for weak phases (restricted to RMM phases 2–5) of the MJO during the monsoon season. Results suggest that the eastward propagation of the MJO over the Indian Ocean modulates rainfall across the India and neighbouring seas and countries – irrespective of the RMM index amplitude. Most works previously published focuses on the diurnal rainfall characteristics of the Indian summer monsoon (JJAS). The present study extends current understanding by investigating diurnal variation in rainfall related to the mean, active, weak and suppressed phases of MJO for each Indian season. Possible drivers of the diurnal cycle of rainfall over the oceans and continental regions were explored using recently reported observational and modelling studies. Our findings help understand rainfall processes for the Indian subcontinent and have practical application for numerical weather prediction, flood forecasting and water resource management regionally.