Wintertime atmospheric rivers and the Karakoram Anomaly: Zero degree line evolution in a changing climate

Keywords: Atmospheric Rivers, High Mountain Asia, Precipitation
Session Type: Virtual Poster Abstract
Day: Sunday
Session Start / End Time: 2/27/2022 03:40 PM (Eastern Time (US & Canada)) - 2/27/2022 05:00 PM (Eastern Time (US & Canada))
Room: Virtual 27

Abstract

Dynamical changes in High Mountain Asia (HMA) have resulted in advancing glaciers in the Karakoram while less than 1 km away in Central Himalaya, glaciers are melting at an accelerated rate. While this has been attributed to changes in these two regions' distinct precipitation regimes - many studies indicate that this anomaly is not fully understood. A recent investigation suggests that 30-60% of wintertime precipitation between 1979 and 2019 occurred on the day following an Atmospheric River (AR) "making landfall" in HMA. This study examines the changes in the freezing level, a key isotherm in mountainous regions, and its influence on rain vs. snow resulting from ARs that reach HMA. Using 36 years of dynamically downscaled reanalyses over High Mountain Asia, we explore the trends related to the zero degree line, or freezing level, and their impact on orographic precipitation resulting from ARs in Western and Central Himalaya. Central Himalaya has been under the influence of a warming anti-cylonic trend, which has significantly increased the frequency and intensity of ARs. Meanwhile, the freezing level has lifted, increasing the rain to snow ratio in CH. The Karakoram, which is at the boundary between cyclonic and anti-cyclonic trends, has experienced increasing frequency of ARs without seeing a significant increase in the freezing level, snowfall or temperature. This study indicates the importance of exploring dynamical changes in HMA via ARs and the contribution of ARs and the freezing level to the observed differences in orographic precipitation between central Himalaya and the Karakoram.