Spatial variations of northeast monsoon rainfall over south peninsular India

This study investigates the spatial variability of Northeast Monsoon (NEM) rainfall over South Peninsular (SP) India, focusing on five meteorological subdivisions: Coastal Andhra Pradesh, Rayalaseema, Tamil Nadu, South Interior Karnataka, and Kerala. AUsing rainfall data from the Indian Institute of Tropical MeteorologyA(IITM), seasonal rainfall patterns are assessed for the NEM period (October-December), Aidentifying active and poor monsoon years based on standardized departures. Composite rainfall values and percentage deviations provide insights into NEM performance across subdivisions. The analysis also explores key meteorological parameters, including lower tropospheric winds, relative vorticity and divergence at 1000 hPa, 850 hPa, and 200 hPa, using NCEP/NCAR Reanalysis datasets from 1948 to 2016. AOutgoing Longwave RadiationA(OLR) Adata from NOAA (1974-2016) Afurther elucidate atmospheric circulation patterns associated with active and poor monsoon years. Findings reveal that active NEM seasons display negative OLR anomalies over SP India and surrounding seas, indicating enhanced convection, particularly in Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu. Conversely, poor monsoons show positive OLR anomalies, signalling reduced convective activity. Wind and divergence anomalies highlight that active monsoons strengthen easterly flows and promote moisture transport to the Intertropical Convergence Zone (ITCZ), Aamplifying rainfall. During poor monsoons, weakened easterlies and reduced atmospheric convergence correspond with diminished rainfall. Notably, El Ni & ntilde;o events generally enhance NEM rainfall, while La Ni & ntilde;a years typically result in deficits, with some exceptions, such as in 2016.