Understanding the driving mechanism for heat waves variability over South Asia during El Niño and La Niña events

Abstract

This study focuses on heat waves (HWs) variability over South Asia (SA) influenced by El Niño Southern Oscillation (ENSO) during 1950–2023. The influence factor and driving mechanism for HWs variability over SA in the El Niño and La Niña years are discussed. We observe positive composite anomalies of HWs events and frequency over the north-western region of SA in La Niña years but negative composite anomalies in El Niño years. In La Niña years, outgoing long-wave radiation (total cloud cover) over the north-western region of SA has positive (negative) anomalies. Thus, less cloud cover regions allow more solar radiation to increase the surface temperature and HWs. During La Niña years, positive composite anomalies of HWs over the north-western region of SA are mainly due to positive anomalies of outgoing long wave radiation, negative anomalies of total cloud cover, positive anomalies of soil temperature level 1, negative anomalies of relative humidity, positive anomalies of short-wave radiation and negative anomalies of long-wave radiation. However, during El Niño years, negative composite anomalies of HWs over the north-western region of SA are due to negative anomalies of outgoing long wave radiation, positive anomalies of total cloud cover, and negative anomalies of direct solar radiation. During El Niño years, vertical-latitude cross-section and vertical-longitude cross-section analysis show significant positive anomalies of air temperature, positive anomalies of vertical velocity, negative anomalies of relative humidity, and positive anomalies of geopotential height; support increases in the HWs over the southern and central -eastern region of SA. These findings give important insights into how future weather patterns may evolve during ENSO events and can contribute to early forecasting and making heat wave adaptation strategies.