LAUSR

The linkages between upper-level westerly jet streams and snow depth over the Tibetan Plateau (TP) in winter (from November to the following April) were investigated for the period 1979–2014 using satellite-borne passive microwave retrievals of snow depth data and ERA-Interim reanalysis data. Anomalies in atmospheric circulation, temperature, and precipitation corresponding to variation in westerly jets were examined to find the causes of variation in snow depth over the TP, using singular value decomposition, composite analysis and dynamical diagnosis. Results show that variation in intensity and meridional shifts of westerly jets, with particular attention to the North Tibetan Plateau jet (NTPJ) and the South Tibetan Plateau jet (STPJ), significantly influence the interannual variation of snow depth over the TP in late winter (February–April). For the conjunction of intense STPJ and weak NTPJ, an anomalous cold low-pressure vortex is observed over the TP. The vortex extends across the TP and spans from the ground surface to the upper troposphere. There is anomalous ascending motion above the TP due to secondary circulations immediately south and north of STPJ, with increased moisture flux from the southwest. These circulation structures cause significant cooling and increased precipitation, thus promoting snowfall and snow accumulation. Temperature is a more important influence than precipitation on snow accumulation. Cooling over the TP is caused by cold temperature advection due to intensely cold air and weakened descending adiabatic heating due to anomalous ascending motion. Local moisture is reduced, and anomalous ascending moisture advection leads to more net precipitation and snowfall over the TP.