Hydraulic jump: The cause of heavy rainfall on the immediate lee side of the Western Ghats in the Maharashtra state of India

Abstract

AbstractNorth–South‐oriented mountains (known as “The Western Ghats [WG]”) running parallel to the west coast of peninsular India separate the Maharashtra state (lying on the northwest of peninsular India) into two meteorological subdivisions (a) Konkan lying on the windward side of WG receiving high monsoon rainfall (2,390 mm) and (b) Madhya Maharashtra (MM) lying on the leeward side receiving low monsoon rainfall (579 mm). The state of Maharashtra has two more subdivisions on the leeward side of WG, viz. Marathwada and Vidarbha, which however do not lie on the immediate leeward side of WG. In this study, a subdivision of MM is further subdivided into (a) north–south strip of 80 km width on the immediate lee side (ILS) from the crest of WG and (b) area extending eastwards from ILS to 280 km, referred to as “distant lee side (DLS).” DLS contains some parts of the Marathwada subdivision also. The study indicates that the mean monsoon rainfall over ILS region is higher than DLS region (proportion is 1.4:1). Higher rainfall over ILS region has been shown due to the occurrence of the “hydraulic jump (HJ).” The dynamics of HJ are explained using Froude number and vertical velocities. The climatological high rainfall over ILS remained an unnoticed feature in the spatial monsoon variability over peninsular India. The study focuses on the unnoticed high rainfall in the ILS region and attributes it to HJ. The incorporation of HJ has the potential to impact on forecasting of monsoon rainfall over the region by numerical models.