The Effects of Continental-Scale Snow Albedo

The NCAR CAM3 GCM with prescribed, satellite-based snow 3 albedo (SA) is used to investigate the remote effects of snow cover on North-4 ern Hemisphere (NH) winter climate. A pair of 100 ensemble member ex-5 periments are integrated through the autumn-winter season, with prescribed 6 high and low SA over Eurasia (EA). Similar to other non-CAM GCM stud-7 ies using prescribed snow mass, anomalous EA snow albedo produces a wave 8 activity pulse that propagates into the stratosphere, culminating in a neg-9 ative phase Arctic Oscillation (AO) like surface response. This occurs for ide-10 alized, but representative SA anomalies, as well as for more realistic SA anoma-11 lies. Similar experiments over North America (NA) and the entire NH are 12 also performed. Unlike prior studies, anomalous NA snow yields a significant 13 AO signal. Here, the local NA surface cooling elicits a transient eddy response, 14 which propagates downstream to Eurasia, resulting in significant, but short-15 lived cooling and upward propagating wave activity over Siberia. A nega-16 tive AO-like response develops, primarily confined to the stratosphere/upper 17 troposphere, which eventually gives way to a tropospheric AO-like response 18 of the opposite phase, due to equatorward wave refraction and wave diver-19 gence. Reanalysis data supports this NA snow-positive AO response. Snow 20 forcing experiments for the whole NH, however, yield a weakened AO sig-21 nal. This is due to a muted wavenumber-1 and-2 response caused by destruc-22 tive interference between the background stationary wave and the correspond-23 ing Rossby wave response, which results in negligible wave activity reach-24 ing the stratosphere.