Large‐Scale Extreme Rainfall‐Producing Synoptic Systems of the Indian Summer Monsoon. Issue 11 (10th June 2020)

• Record Type: Journal Article
• Authors: Nikumbh, Akshaya C.; Chakraborty, Arindam; Bhat, G. S.; Frierson, Dargan M. W.
• Is Part Of: Geophysical research letters. Volume 47:Issue 11(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-10
• Subjects: extreme rainfall events -- low‐pressure systems -- interaction of cyclonic vortices; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088403
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: In recent years India has been increasingly experiencing widespread floods induced by large‐scale extreme rainfall events (LEREs). LEREs are mainly associated with monsoon low‐pressure systems (LPS). The forecast of these high‐flood‐potential events, however, has remained challenging. Here, we compare LPSs of the summer monsoon that led to LEREs (LPS‐Lg) and strong LPSs that did not result in LEREs (LPS‐noLg) over central India for the period 1979–2012. We show that having a strong LPS is not a sufficient condition to produce LEREs, and the LPS‐Lgs are accompanied by secondary cyclonic vortices (SCVs). The simultaneous existence of an LPS and an SCV creates a giant midtropospheric vortex. SCVs enhance dynamic lifting, static instability, and moisture transport from the Arabian Sea that precondition the atmosphere for deep convection. SCVs also slow down the propagation of LPSs. We show that the interaction of synoptic‐scale systems can lead to LEREs even if individual systems are not strong enough. Plain Language Summary: Over the past two decades, India has endured many widespread floods caused by large‐scale heavy rainfall events during the monsoon season that resulted in huge losses to life and property. The large‐scale heavy rainfall events, though rare, have become more frequent recently. We show that these events occur when multiple monsoon low‐pressure systems are present at the same time. While the individual systems themselves need not be very strong, their simultaneous presence makes the environment conducive for sustained and organized deep convection, leading to large‐scale heavy rainfall events over central India. Key Points: A mechanism for large‐scale extreme rainfall events of central India is proposed Large‐scale extreme rainfall events occur when monsoon low‐pressure systems are assisted by secondary cyclonic vortices The interaction of two cyclonic vortices form conditions favorable for long‐lived, organized, and slow‐moving convective systems