Linking Siberian Snow Cover to Precursors of Stratospheric Variability and Intraseasonal Predictability
Monday, 15 December 2014
Previous research has linked wintertime Arctic Oscillation (AO) variability to indices of Siberian snow cover and upward wave activity flux in the preceding fall season. Here, daily data is used to examine the surface and tropospheric processes that occur as the link between snow cover and upward forcing into the stratosphere develops. Spatially, the area of October snow with highest correlations to the mean snow cover index occurs in northwestern Siberia, and is co-located with lagged direct relationships to sea level pressure (SLP) and to lower-stratosphere (100hPa) meridional heat flux. Analysis of daily SLP and 100hPa heat flux shows that in years with high October snow, the SLP is significantly higher from approximately 1 November to 15 December, and the 100hPa heat flux is significantly increased with a two-week lag, from approximately 15 November to 31 December. During Nov-Dec, there are periods with upward wave activity flux extending coherently from the surface to the stratosphere, and these events occur nearly twice as often in high snow years compared to low snow years. The vertical structure of these events is a westward-tilting pattern of high eddy heights, with largest normalized anomalies near the surface in the same region as the snow and SLP changes. These results suggest that high SLP develops in response to the snow cover and this higher pressure, in turn, provides part of the structure of a surface-to-stratosphere wave activity flux event, thus making full events more likely. Implications for improved winter climate forecasts on intraseasonal to seasonal timesscales for the Northern Hemisphere high- and mid-latitudes exist through recognition of these precursor signals.