This study examines the influence of the El Niño-Southern Oscillation (ENSO) phases on spring heatwaves over Northwestern South Asia (NWSA) from 1976 to 2024. The composite of La Niña and El Niño phases shows that during the La Niña phase, the subtropical westerly jet shifts to higher latitudes (~ 444 km at 77°E and ~ 333 km at the other longitudes over the NWSA) compared to the El Niño phase. We analyze the northward shift of the subtropical westerly jet index (SWJI) for March-April-May (92 days/season) from 1976 to 2024. During La Niña, the SWJI exhibits frequent northward shifts (32.18 days/season) compared to the El Niño phase (21.20 days/season). During the La Niña phase, the subtropical westerly jet shifts to a higher latitude, reducing upper-level westerlies and strengthening anticyclonic circulation over NWSA (increased geopotential height at 200–500 hPa), enhancing subsidence (increased vertical velocity at 200–700 hPa). Thus, enhanced net surface shortwave radiation, reduced precipitation, and warmer soils create conditions conducive to increased heatwave frequency (HWF) and heatwave cumulative intensity (HWI) over NWSA during the La Niña phases. In the La Niña phase, the area-averaged HWF (9.15 days/season) and HWI (14.10 °C/season) increased compared to the El Niño phases (HWF: 3.40 days/season and HWI: 3.66 °C/season) by 169% and 285% respectively, over the NWSA region. These findings establish the subtropical westerly jet as a teleconnection pathway linking ENSO to NWSA heatwaves.
Adhikari et al. (Sun,) studied this question.