Large-scale extreme rainfall producing synoptic systems of the Indian
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-Lg are accompanied
by Secondary Cyclonic Vortices (SCVs). The simultaneous existence of LPS
and SCV creates a giant mid-tropospheric 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
aren’t strong enough.