Influence of ENSO and Volcanic Eruptions on Himalayan Jet Latitude

The position of the subtropical jet over the Himalayas (Himalayan jet) affects extreme precipitation and heat over Central and South Asia. We examine the influence of two major natural factors-the El Ni & ntilde;o/Southern Oscillation (ENSO) and explosive volcanic eruptions-on Himalayan jet interannual variability during the past millennium using simulations from the Community Earth System Model. We find that both El Ni & ntilde;o events and eruptions shift the Himalayan jet equatorward by up to 3 degrees. If an El Ni & ntilde;o occurs following an eruption, this enhances the equatorward Himalayan jet shift, while La Ni & ntilde;a tends to favor poleward jet migration. Subtropical cooling during El Ni & ntilde;o or following eruptions is the primary cause of equatorward Himalayan jet shifts, while poleward shifts are associated with subtropical warming. Consistent across the CMIP6 models over the historical period, our results suggest that both ENSO and eruptions are the key drivers of interannual Himalayan jet variability. The latitudinal position of the jet stream over the Himalayas (the Himalayan jet) affects storms and heat waves in Central and South Asia. Because changes in the sea surface temperature over the tropical Pacific Ocean (the El Ni & ntilde;o Southern Oscillation, or ENSO) and large volcanic eruptions are the major sources of year-to-year climate variability, we examined their impacts on north-south displacements of the Himalayan jet latitude over the past millennium using climate model simulations from the Community Earth System Model. We find that both El Ni & ntilde;o events and volcanic eruptions move the jet toward the equator, while La Ni & ntilde;a events move the jet poleward. These jet displacements happen because both ENSO and volcanic eruptions change subtropical temperatures. When the tropospheric subtropics cool, equatorward jet shifts occur, while the reverse is true for poleward jet shifts. Our results are also consistent across a set of global climate models over the past 150 years. Climate models show equatorward shifts of Himalayan jet during El Ni & ntilde;o events and in the 0-2 years following volcanic eruptions El Ni & ntilde;o events following eruptions amplify jet migration, while ENSO-neutral post-eruption conditions tend to have a weaker impact Poleward (equatorward) displacement of the jet is caused by tropospheric warming (cooling) over the subtropics