Mechanism of winter precipitation variations in the southern arid Central Asia

Abstract

AbstractThe southern arid central Asia (SACA, 35.25°–45°N, 46.25°–80°E) is influenced by Mediterranean type of climate with wet cool season. This study analysed the variations of winter precipitation and their mechanisms during 1979–2017. The results suggest the variations of winter precipitation in SACA are influenced by two water vapour pathways, which are closely linked to a low‐latitude high‐pressure anomaly near Indian subcontinent and the mid‐high latitude North Atlantic Oscillation (NAO), respectively. Specifically, at low latitudes, the northern Indian Ocean heated by El Niño causes the anomalous intensification of the subtropical high throughout the low latitude region, especially over the Indian subcontinent, resulting in increased water vapour transport from the northern Indian Ocean to SACA. This result of low latitude is also supported by model simulations. At middle and high latitudes, the negative NAO phase leads to a southward displacement of the water vapour pathway and carries water vapour to pass over number of upwind water bodies, resulting in the transport of more westerly‐associated water vapour to SACA. Further analysis showed that there is a northwest‐southeast teleconnection wave train, from the North Atlantic to Central Asia and to the Indian subcontinent, which allows wave fluxes originating in the North Atlantic and the northern Indian Ocean to propagate from high and low latitudes, respectively, to the study area. At the same time, high‐latitude cold air advection, brought by the low‐pressure system in Central Asia, converges with the flow of warm water vapour from the low‐latitude northern Indian Ocean, generating an ascending motion and reducing atmospheric static stability, and thereby lead to increasing precipitation in SACA. Therefore, the key to determining the origin of precipitation variations in SACA is understanding the interaction of large‐scale circulation systems at low and mid‐high latitudes.Key wordsarid Central Asia, precipitation, dynamic mechanism