Interannual Variability of Snow Depth over the Tibetan Plateau and Its Associated Atmospheric Circulation Anomalies

The interannual variability of wintertime snow depth over the Tibetan Plateau (TP) and related atmospheric circulation anomalies were investigated based on observed snow depth measurements and NCEP/NCAR reanalysis data. Empirical orthogonal function (EOF) analysis was applied to identify the spatio-temporal variability of wintertime TP snow depth. Snow depth anomalies were dominated by a monopole pattern over the TP and a dipole structure with opposite anomalies over the southeastern and northwestern TP. The atmospheric circulation conditions responsible for the interannual variability of TP snow depth were examined via regression analyses against the principal component of the most dominant EOF mode. In the upper troposphere, negative zonal wind anomalies over the TP with extensively positive anomalies to the south indicated that the southwestward shift of the westerly jet may favor the development of surface cyclones over the TP. An anomalous cyclone centered over the southeastern TP was associated with the anomalous westerly jet, which is conducive to heavier snowfall and results in positive snow depth anomalies. An anomalous cyclone was observed at 500 hPa over the TP, with an anomalous anticyclone immediately to the north, suggesting that the TP is frequently affected by surface cyclones. Regression analyses revealed that significant negative thickness anomalies exist around the TP from March to May, with a meridional dipole anomaly in March. The persistent negative anomalies due to more winter TP snow are not conducive to earlier reversal of the meridional temperature gradient, leading to a possible delay in the onset of the Asian summer monsoon.