IPA - IOP | Cockcroft - Walton Lecture Series 2020

Title: Understanding mid-latitude influences on the Indian region

While India’s annual cycle of rainfall is dominated by the summer monsoon, some rainfall, often extreme, reaches the north of the country during winter in the form of Western Disturbances, which are poorly studied. Western Disturbances pass along the upper-tropospheric subtropical westerly jet, with a dynamical signature originating as far away as the Mediterranean or further afield, while moisture is collected from the northern Indian Ocean.  This talk introduces the results of the recently completed BITMAP project that has developed a tracked database of Western Disturbances and examines their seasonal cycle, role in extreme events and typical structure.

Motivated by work elsewhere (chiefly over the Atlantic) that has examined the impact of polar warming on the large-scale meridional temperature gradients on which the jet sits, we show the effect of historical warming on the subtropical westerly jet over Eurasia and its impact on Western Disturbances.  We also examine their behaviour in the Representative Concentration Pathways – the emissions scenarios used in future climate projection – to determine expected change in the track, intensity or frequency of Western Disturbances and any impact on the rainfall received.