Predictability of snow-depth anomalies over Eurasia and associated circulation patterns

This study investigates the variability and predictability of snow depth an omalies over the Eurasian continent at the end of winter, as represented in 12 ensembles of General Circulation Model simulations performed at the Eur opean Centre for Medium-Range Weather Forecasts. Each ensemble includes nin e integrations performed with the same prescribed sea surface temperature, but started from time-lagged initial conditions. An empirical orthogonal fu nction (EOF) analysis shows that the leading EOF of Eurasian snow depth in March has a zonally-oriented dipole structure, with a band of positive anom alies covering northern Europe and Siberia, and negative anomalies over cen tral Europe, the Himalayas and north China. A significant relationship is f ound between the positive/negative phase of this snow-depth anomaly and war m/cold El Nino Southern Oscillation events. The positive phase of the snow- depth EOF1 is associated with a wintertime circulation characterized by a s trengthening of the westerly winds over Europe and Siberia; in the upper tr oposphere, this westerly anomaly is accompanied by negative zonal wind anom alies over Eurasia around 30-40 degrees N and positive zonal wind anomalies between the equator and 25 degrees N over Africa and south-east Asia. A go od degree of predictability is found in the snow-related circulation anomal ies: considering 500-hPa height, 850-hPa zonal wind and 200-hPa zonal wind, the interannual variations of the ensemble-mean fields show a correlation of 48%, 56% and 65% (respectively) with the corresponding observed anomalie s over the eastern half (0 degrees to 180 degrees E) of the northern hemisp here. The tropical component of the zonal wind anomaly associated with snow -depth EOF1 is strongly predictable; it shows a marked persistence from win ter to the early summer, and affects the large-scale circulation over south Asia in the early and central periods of the monsoon season.