Controls on Northern Hemisphere snow albedo feedback quantified using satellite Earth observations

Variations in the strength of the current spring snow albedo feedback (SAF) over Northern Hemisphere land surfaces (NH) explain over one third of the 21 century temperature response to anthropogenic forcings in this region within global circulation model (GCM) projections. Observation based estimates of controls on SAF are needed to constrain the snow and albedo parameterizations in these models. The total April-May NH SAF, corresponding to the sum of the effect of temperature on surface albedo over snow covered surfaces (‘metamorphism’) and over surfaces transitioning from snow covered to snow free conditions (‘snow cover’), is derived with daily NH snow cover and surface albedo products derived from Advanced Very High Resolution Radiometer Polar Pathfinder satellite data and surface air temperature from ERA40 reanalysis dataset between 1982-1999. The estimated total NH SAF of -0.93 ± 0.06 %K, for land surfaces north of 30oN, was not significantly different (P<0.05) from estimates based on International Satellite Cloud Climatology Project surface albedo data. Both ‘snow cover’ and ‘metamorphosis’ components had a similar magnitude of ~-0.5 %K. The SAF pattern was significantly correlated with ‘snow cover’ factor patterns over both North America and Eurasia but only over Eurasia with the ‘metamorphosis’ component. Unlike GCM model based analysis, the observational ‘snow cover’ feedback factor related to the albedo contrast of snow covered and snow free surfaces was not significantly spatially bcorrelated to the total SAF. However, only this factor and the total SAF sensitivity were found to be relatively unaffected by internal climate variability.