Title: Impact of Large-Scale Warming on Intraseasonal Variability of Indian Summer Monsoon Rainfall
Abstract: Abstract Indian summer monsoon, a part of the Asian summer monsoon is defined as the seasonal reversal of atmospheric circulation, is manifested in the form of northward migration of Inter-Tropical Convergence Zone (ITCZ) with respect to its normal position over the equator and resulting precipitation caused by the cross-equatorial moisture-laden south-westerly winds over the Indian subcontinent. Indian summer monsoon which is a complex geophysical phenomenon possesses a wide spectrum of variabilities such as daily, intraseasonal, interannual, decadal, and so on. The interaction between multiple modes of propagating intraseasonal oscillations of the Indian summer monsoon causes intermittent wet spells (i.e. active spells with good rainfall) and dry spells (i.e. breaks with little rainfall) over core monsoon zone. It is argued that a prolonged dry spells during July-August and an uneven temporal and spatial distribution of rains (even in normal monsoon years) has potential to have an adverse effect on agriculture. Therefore, understanding of the intraseasonal variation and the occurrence of the breaks, their intensity, and duration is very important. Indian summer monsoon region is vulnerable to global warming which is evident in the form of an increasing number of extremes and the increasing spatial variability of rainfall. The main focus of the study is to understand the nature of the break and characteristics of the break over all India monsoon regions and how active and break will vary with warming? This study investigates the impacts of warming on the core monsoon zone and all India monsoon regions by using the output of the ‘Half a degree Additional warming Prognosis and Projected Impacts’ (HAPPI) experiment model. There are five AGCM models are used in this study such as NorESM1-HAPPI, ECHAM6.3-LR, CanAM4, MIROC5, and , CAM4-2degree . Both, inter-model and intra-model comparisons are performed based on indicators such as the frequency and length of active and break spells for the historical period, plus15 period, and plus20 period (future). Vertically Integrated Moisture Transport (VIMT) pertaining to active and break is also analysed. An increase in moisture transport in the future active period under 1.5°C warming condition (plus15 future) and under 2°C warming condition (plus20 future) is expected in NorESM1-HAPPI model with intensification of rainfall over the core monsoon zone. Similarly, there will be intensification of breaks, and the core monsoon zone will receive less atmospheric moisture in future breaks under 1.5°C warming condition (plus15 future) and under 2°C warming condition (plus20 future).