Summer Research Fellowship Programme of India's Science Academies

Recent changes in summer monsoon onset dates over South and East Asia

N. Padmageetha

College of Engineering Guindy, Anna University, 12, Sardar Patel Road, Guindy, Chennai, Tamil Nadu 600025

Dr. Arindam Chakraborty

Indian Institute of Science, CV Raman Road, Bengaluru, Karnataka 560012


The onset of Asian Summer Monsoon is characterised by a sudden transition in several atmospheric parameters like rainfall, kinetic energy and vertical profile of vertical winds. The onset isochrones start from South China Sea in May and advance toward northwest to reach Indian peninsula by early June. However, there is substantial interannual variations to this propagation of onset isochrones. As summer monsoon creates a large impact on the Indian economy, it is very important to know the spatio-temporal variations of the onset dates. This study focuses on the spatial and temporal changes of summer monsoon onset dates over South and East Asia for the two sets of climatological period of years (1979 - 1998 and 1999 - 2016). Precipitation is used as a parameter to identify the onset dates over the entire south and east Asia in this work. The regions which face the monsoon are further divided into several smaller regions based on the onset pentad dates to understand and analyze the spatial variations of onset dates. Surface pressure, precipitable water and wind parameters were analysed over South and East Asia for 38 years. Further analysis is made on the climatological onset dates with surface pressure, precipitable water and wind to study their spatial and temporal variations.

Keywords: monsoon onset, surface pressure, precipitable water, wind, precipitation

Written, reviewed, revised, proofed and published with