Influence of Anomalous December Snow Cover over North America on January mid-high latitude Asian Surface Air Temperature

This study suggests that the variations of December North American (NA) snow cover are highly correlated with January anomalous surface air temperature (SAT) over mid-high latitude Asia. On the one hand, in December, the increased NA snow cover enlarges the meridional SAT gradient between 20°N and 50°N, which strengthens the 300-hPa westerly jet stream over the North America−North Atlantic sector and the transient eddies in the exit region of the jet. In January, both the positive transient eddy anomalies and 300-hPa zonal wind anomalies move eastward over the Eastern North Atlantic, due to a positive feedback. On the other hand, the strengthened surface northwesterly winds over the North America−North Atlantic sector in December induces negative sea surface temperature downstream of the landmass around 40°N, which can persist into January and then cause negative transient eddy anomalies over the Western North Atlantic. Taken together, there is a dipole-distributed transient eddy anomaly pattern over the North Atlantic (25−50°N, 75°W−5°E) in January, which favors northwest-southeast tilting anticyclone in this region. The anticyclone anomalies further induce an anomalous ocean−atmosphere interaction, which contributes to the eastward extension of the wave train by inducing upward and eastward-propagating wave pulses. The wave train propagates across Eurasia and induces a westward extension of Siberian High, a strengthened and southward-shifted East Asian jet stream and an enhanced East Asian Trough, causing southward advection of cold air and decreased SAT over mid-high latitude Asia. The finding provides a new factor for the prediction of January SAT over mid-high latitude Asia.