Interactions between Northern Hemisphere Snow Cover and the Troposphere Circumpolar Vortex

Potential linkages between Northern Hemisphere land mass snow cover (NHSC) and the troposphere circumpolar vortex (CV) for the last 50 year period (1967-2016) are examined. Monthly CVs are derived from the NCEP-NCAR reanalysis I 500hPa geopotential height data set and NHSC anomalies generated at the Rutgers University Global Snow Lab are compared with the size and circularity ratio of CV. Correlation analyses demonstrate that April-July NHSC has significant positive (negative) correlations with August-October CV size (circularity ratio), while January-March CV size (circularity ratio) correlates positively (negatively) with April-June NHSC. Time series data show decadal variations in autumnal NHSC with positive anomalies since late 20^th century in spite of global warming, while vernal NHSC show a persistent decreasing trend over the entire study period. These results indicate that disappearing vernal NHSC in a warmer climate may lead to the poleward retreat of late summer CV with less meandering. Thus, it is expected that the reduction of vernal NHSC may provide a favorable condition for extended hot summers at the lower mid-latitudes through snow albedo feedback associated with the poleward shrinkage of CV.