Summary of Abstract Submission

Abstract Submission No. IO50-05-0022PresentationPoster

IMPACT OF ATMOSPHERIC MOISTURE TRANSPORT ON INDIAN SUMMER MONSOON ONSET AND WITHDRAWAL

AMEY PATHAK*1, A S SAHANA1, Dr. SUBIMAL GHOSH1

1 Department of Civil Engineering, IIT Bombay, India

ABSTRACT :

The simulation of Indian Summer Monsoon Rainfall (ISMR), especially its onset, is very crucial as most of the agricultural practices depend on it. The onset (monsoon onset at western coast) and withdrawal of the ISMR displays substantial interannual variability, which is traditionally linked to sea surface temperature (SST) anomalies over the tropical Pacific Ocean, and land surface feedback over the Indian subcontinent respectively. In the present study we examine the impact of SST anomalies, and feedback of land surface evapotranspiration to ISMR. We observe that the early ISMR onset years are associated with high amount of moisture transport from western Indian Ocean. Also, we see that the late development of easterly vertical shear, which reduces the northward-propagation of intraseasonal variability during May┐June, results in delayed onset. The deficit rainfall years are associated with delayed onset and early withdrawal of ISMR, which is due to weak oceanic moisture transport at the start of monsoon and lesser amount of recycling during September. It is to be noted that the warming shift of tropical Pacific SST during 1976/1977 has resulted in a delayed shift of ISM onset. The novelty of present work lies in understanding the role the Indian Ocean, the tropical Pacific and sub continental terrestrial sources on ISMR during deficit and surplus rainfall years. Our findings also highlight the need for the re-assessment of the crop calendar in India, which is now based on the mean onset date computed from long-term data, without considering the regime shift or trends in onset.