Subrahmanyam (Subra) Bulusu
Professor, Satellite Oceanography & Physical Oceanography
School of the Earth, Ocean, and Environment
University of South Carolina, Columbia

Intraseasonal oscillations (ISOs) significantly contribute to the variability and strength of heavy rainfall associated with the Indian Summer Monsoon. Northwardpropagating ISOs contribute to an increase in momentum and moisture from the tropical Indian Ocean to the Indian subcontinent that intensifies monsoonal rainfall rates. The atmospheric systems associated with monsoonal ISOs (such as Madden Julian Oscillations (MJO), quasi-biweekly oscillations, and synoptic events) induce shifts in circulation that directly impact the strength and timing of active and break monsoon periods, which are respectively characterized by wet and dry conditions. Here we examine the relationship between ISOs and monsoon strength by comparing how monsoonal rainfall and the tropical convergence zone (TCZ) fluctuate in years with strong and years with weak ISOs. The positioning and synoptic structure of the TCZ and how it responds to ISO-related shifts in circulation are essential for improved predictability of the strength and timing of the summer monsoon onset. This novel research explores the variability of the Indian Summer Monsoon over multiple ISO periods to quantify the individual contributions from the MJO (at a 30-90 day periodicity), quasi-biweekly oscillations (at a 10-20 day periodicity) and synoptic scale events from oscillations in the monsoon trough (at a 3-7 day periodicity). This study utilizes in situ, satellite observations and NOAA’s Climate Forecast System version 2 (CFSv2) to investigate and quantify the dynamical relationship between ISOs and Indian Summer Monsoon variability.