Northern Hemisphere snow cover and atmospheric blocking variability

Abstract

The interseasonal relationship between Northern Hemisphere (NH) snow cover and regional blocking patterns is explored for a 31-year data set. It is found that snow cover exerts an important influence on regional atmospheric blocking, which, in turn, modulates snow cover extent at subcontinental scales. Observational results provide strong evidence of two primary linkages in the seasonal snow cover-blocking relationship that support an interannual persistence cycle: The first one links winter blocking over the Atlantic and the subsequent spring (summer) Eurasian (North American) snow cover anomalies; the second one implies that spring (summer) Eurasian (North American) snow cover precedes an anomalous winter Atlantic blocking activity. We describe the temporal stages of the snow cover-blocking relationship in the framework of a six-step conceptual model. According to that, an enhanced Atlantic blocking activity in winter favors a later spring snow disappearance through an enhanced cold advection toward western Eurasia. The resulting snow cover anomalies partially force an opposite-sign blocking response over west and central Pacific which is sustained through spring and early summer, presumably because of the persistence of snow cover anomalies. This anomalous pattern seems to play a role in the propagation of snow cover anomalies from Eurasia in spring to the Hudson’s Bay region of North America in summer. The excessive snow cover over this region induces an asymmetrical temperature distribution, which, in turn, favors blocking activity over Europe and the West Pacific. The connection between autumn and winter climates is not clear but it could be related with the ability of autumn high ATL blocking activity to determine an early snow cover appearance in October over western Eurasia. This linkage completes a snow cover-blocking cycle of interactions which identifies snow cover as a candidate for the recently observed blocking trends and a contributor to the interannual persistence of winter climate.