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<p>Heat waves have become a critical concern globally due to their severe societal and sectoral impacts. This study explores the mechanisms linking El-Niño Southern Oscillation (ENSO) with maximum temperature and heat wave variability over India during boreal spring, using observational and reanalysis data. Our analysis reveals a dipole pattern in maximum temperatures and heatwave days, with above (below) normal maximum temperatures and increased (reduced) heatwave days in southern peninsular India (central and northwest India) during El Niño and opposite pattern observed during La Niña events. The distribution of sea surface temperatures (SSTs) during El Niño (La Niña) events over the equatorial Pacific, along with anomalously warmer (cooler) Indian Ocean conditions, affects the tropospheric temperature gradient between the Indian Ocean and Indian landmass. A stronger (weaker) tropospheric temperature gradient during El Niño (La Niña) drives the southward (northward) shift of the Hadley circulation. This shift, in turn, affects the dynamics of the subtropical westerly jet stream (STWJS), causing it to migrate southward (northward) during the positive (negative) phase of ENSO. During El Niño events, the southward shift of the STWJS lowers the 0&#xa0;°C isotherm, while moisture influx from the northern Indian Ocean enhances convective instability, leading to increased precipitation and fewer heatwaves over northern India. Conversely, anticyclonic circulation and moisture divergence over southern peninsular India suppresses convection, resulting in above-normal temperatures and more frequent heatwaves. This pattern was found to be reversed during the La Niña. The impact of heat distribution during the ENSO phases and associated changes in the boundary layer dynamics are also discussed.</p>

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On the dynamics of ENSO linked contrasting heat wave patterns over the Indian region

  • 期刊论文

  • 发表日期：

    2025年4月5日

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  • S. D. Sanap,
  • P. Priya,
  • J. S. Chowdary,
  • D. R. Pattanaik

摘要

Heat waves have become a critical concern globally due to their severe societal and sectoral impacts. This study explores the mechanisms linking El-Niño Southern Oscillation (ENSO) with maximum temperature and heat wave variability over India during boreal spring, using observational and reanalysis data. Our analysis reveals a dipole pattern in maximum temperatures and heatwave days, with above (below) normal maximum temperatures and increased (reduced) heatwave days in southern peninsular India (central and northwest India) during El Niño and opposite pattern observed during La Niña events. The distribution of sea surface temperatures (SSTs) during El Niño (La Niña) events over the equatorial Pacific, along with anomalously warmer (cooler) Indian Ocean conditions, affects the tropospheric temperature gradient between the Indian Ocean and Indian landmass. A stronger (weaker) tropospheric temperature gradient during El Niño (La Niña) drives the southward (northward) shift of the Hadley circulation. This shift, in turn, affects the dynamics of the subtropical westerly jet stream (STWJS), causing it to migrate southward (northward) during the positive (negative) phase of ENSO. During El Niño events, the southward shift of the STWJS lowers the 0 °C isotherm, while moisture influx from the northern Indian Ocean enhances convective instability, leading to increased precipitation and fewer heatwaves over northern India. Conversely, anticyclonic circulation and moisture divergence over southern peninsular India suppresses convection, resulting in above-normal temperatures and more frequent heatwaves. This pattern was found to be reversed during the La Niña. The impact of heat distribution during the ENSO phases and associated changes in the boundary layer dynamics are also discussed.