Arctic Oscillation and the autumn/winter snow depth over the Tibetan Plateau

Abstract

The present study examines the relationship between the Arctic Oscillation (AO) and the autumn/winter snow depth over the Tibetan Plateau. Results show that there exists significant correlation between the AO and the Tibetan Plateau snow depth on interdecadal time scale. The AO and the snow depth over the Tibetan Plateau experienced interdecadal regime shift in the late 1970's. Before the late 1970's when the AO was in its interdecadal negative phase, the snow depth over the Tibetan Plateau increased in fall, and then decreased in following winter. On the contrary, when the AO has entered its interdecadal positive phase since the early 1980's, the snow depth decreased in fall, but increased in winter. The vertical propagation of Rossby waves is proposed to explain the physical process linking the AO with the snow depth. Anomalously excessive fall snow depth over the Tibetan Plateau amplifies orographically forced upward stationary waves. The snow-forced changes in stratosphere are not identified until later in the winter season when Rossby waves propagate into the stratosphere and the AO becomes negative. In winter, when the troposphere and stratosphere are actively coupled, the downward propagation of Rossby waves associated with the positive AO phase modulates the atmospheric circulation in the troposphere, and causes the abnormal increase of snow depth over the Tibetan Plateau.