Heat wave characteristics over India during ENSO events

El-Nino Southern Oscillation (ENSO) is a major ocean-atmospheric coupled phenomenon in the Tropical Pacific Ocean that influences the Indian summer-time temperatures during April and May. In the current analysis, we examined the impact of ENSO on Indian heat waves. Temperature zones are identified when the maximum temperature exceeds 42 degrees C, particularly during April and May over the Indian subcontinent. The results depicted three different regions (west Rajasthan, northwest and southwest UP, and south-central India) that experienced the frequency in days with maximum temperature above 42 degrees C. These means are compared with those of Preceding El Nino (PEN), El Nino (EN) and Succeeding El Nino (SEN) events. It is found that PEN and SEN years experienced high positive anomalies. It can be seen that an increase in surface temperatures and heat waves are closely associated with the strengthening of north-westerlies and reduction of geopotential height at 500 hPa level, reduction of soil moisture and increase of sea surface temperatures (SST) during PEN and SEN events. The results also show that the variations in temperature and heat waves over northeast India are different from the rest of India during EN and SEN years. The three maximum temperatures regions of (1) west Rajasthan, (2) east Uttar Pradesh, and (3) Vidarbha, are identified based on both the magnitude and frequency days of above 42 degrees C maximum temperatures. The spectrum analysis is performed for the monthly time series of the days exceeding daily surface maximum temperature 42 degrees C for the three regions and identified the dominant periodicities with 2.2-2.8 and 3.3-8.5 years, which could be endorsed to ENSO and QBO frequencies.

Automated summary

The El-Nino Southern Oscillation (ENSO) has a significant impact on heat waves in India, particularly in regions like west Rajasthan, northwest and southwest Uttar Pradesh, and south-central India. Years preceding and succeeding El Nino events tend to experience high positive anomalies in surface temperatures and heat wave frequency, attributed to changes in atmospheric circulation and environmental conditions. Different regions in India exhibit variations in temperature and heat waves during El Nino and post-El Nino years, with periodicities of 2.2-2.8 and 3.3-8.5 years likely influenced by ENSO and Quasi-Biennial Oscillation (QBO) frequencies.