ENSO-induced Latitudinal Variation of the Subtropical Jet Modulates Extreme Winter Precipitation over the Western Himalaya

In this study, we investigate the complex relationship between western disturbances (WDs), the El Niño–Southern Oscillation (ENSO), and extreme precipitation events (EPEs) in the western Himalaya (WH) during the extended winter season (November–March). WDs west of WH coincide with 97% of recorded EPEs, contributing substantially (32% in winter, 11% annually) to total precipitation within WH. WDs are 6% less frequent and 4% more intense during El Niño than La Niña to the west of WH. During El Niño (compared to La Niña) years, WDs co-occurring with EPEs are significantly more intense and associated with 17% higher moisture transport over “WH box” (the selected region where most of the winter precipitation over WH occurs). This results in twice the EPE frequency during El Niño periods than La Niña periods. A substantial southward shift (∼180 km) of the subtropical jet (STJ) axis during El Niño brings WD tracks further south towards their primary moisture sources, especially the Arabian Sea. We have shown that WDs that are both more intense and pass to the south of their typical latitudes have higher levels of vertically integrated moisture flux (VIMF) within them. VIMF convergence in the most intense pentile of WDs is 5.7 times higher than in the weakest, and is 3.4 times higher in the second lowest latitude pentile than in the highest. Overall, this study demonstrates a direct link between changes in the latitudinal position and intensity of WDs associated with the winter STJ, and moisture convergence, which leads to the occurrence of EPEs over WH during ENSO phases.