What caused the unseasonal extreme dust storm in Uzbekistan during November 2021?

Abstract

An unseasonal dust storm hit large parts of Central Asia on 4-5 November 2021, setting records for the column aerosol burden and fine particulate concentration in Tashkent, Uzbekistan. This dust storm originated from an agropastoral region in southern Kazakhstan, where the soil erodibility was enhanced by a prolonged agricultural drought resulting from La Niña-related precipitation deficit and persistent high atmospheric evaporative demand. The dust outbreak was triggered by sustained postfrontal northerly winds during an extreme cold air outbreak. The cold air and dust outbreaks were preceded by a chain of processes consisting of recurrent synoptic-scale transient Rossby wave packets over the North Pacific and North Atlantic, upper-level wave breaking and blocking over Greenland, followed by high-latitude blocking over Northern Europe and West Siberia, and the equatorward shift of a tropopause polar vortex and cold pool into southern Kazakhstan. Our analysis suggests that the historic dust storm in Uzbekistan was a compound weather event driven by cold extreme, high winds, and drought preconditions.