Shifted Diurnal Cycle of Indian Summer Monsoon Rainfall

Abstract

One of the most prominent weather and climate variations occurs at diurnal time scale, synchronously or asynchronously with the top of the atmosphere insolation. The corresponding variations in energy budget, specifically concerning moist convection, interacts with the mean climate. Using station-based hourly observations over India, we show that phase of rainfall diurnal cycle during summer monsoon season experienced spatially homogeneous shifts in recent epoch (1992–2014) compared to the past (1969–1991). While the central, north and south peninsular India, comprising about 55% of the stations, experience a delayed phase in recent epoch, an advancement in phase is observed over relatively smaller regions like northeast and northwest India. Further analysis showed that enhanced frequency (intensity) of heavy rainfall events later (earlier) in the afternoon is responsible for the delay (advance) in the mean diurnal phase over central (northwest) India. Our study indicates large-scale shift in the monsoon diurnal cycle with climate change.