Tropical-extratropical interactions during large-scale extreme rainfall events over central India

Large-scale extreme rainfall events (LEREs, area ≥70 × 103 km2) over central India are produced by monsoon low-pressure systems when assisted by a secondary cyclonic vortex (SCV). Both the monsoon low and SCV are embedded in a monsoon trough and form mainly during the positive phase of monsoon intra-seasonal oscillations. Here, we show that tropical-extratropical interactions exist during LEREs. First, we examine if extratropical Rossby waves can come over the Indian subcontinent during the boreal summer. Using the ray tracing technique, we show that stationary Rossby wave rays originating over the north Atlantic can come over India at mid-levels, following approximately the great circle path. Using reanalysis data, we find that this pathway plays a crucial role in tropical-extratropical interactions during LEREs. LEREs are preceded by the Atlantic blocking high and a quasi-stationary central Asian high. We will discuss how extratropical disturbances interacts with equatorial monsoon trough during LEREs.