Ground-Based and Satellite-Derived Measurements of Surface Albedo on the North Slope of Alaska

Abstract

Spatial and temporal variations of surface albedo on the North Slope of Alaska were investigated using both ground-based tower measurements and satellite remote sensing data. Ground-based measurements of incident and reflected solar radiation at several stations along the Dalton Highway over the period 1985?98 are used to determine in situ surface albedo. Advanced Very High Resolution Radiometer (AVHRR)-derived surface albedo were obtained from AVHRR Polar Pathfinder products, available from the National Snow and Ice Data Center, using a modified cloud mask. AVHRR-derived surface albedo agrees closely with in situ measurements. Results from this study indicate that surface albedo varies from greater than 0.9 for a snow-covered land surface under overcast conditions to less than 0.1 for a wet tundra land surface. Five distinct temporal periods are discerned, based on seasonal variations of surface albedo: winter stationary, spring snowmelt, postsnowmelt, summer stationary, and autumn freeze-up periods. Spatially, the North Slope is divided into three zones based on patterns of seasonal variation in surface albedo. A mountain zone is along the ranges and slopes of the Brooks Range, with elevations above 1000 m. When compared with the other two zones, surface albedo in this zone is the lowest in winter, varying from 0.4 to 0.7, and relatively high in summer, from 0.15 to 0.2. The foothills zone is along the foothills of the Brooks Range, with elevations from 300 to 1000 m. Surface albedo is relatively high in this zone in winter (0.8) and the highest in summer (0.2). Surface albedo in this zone changes very rapidly from 0.8 to 0.2 within a couple of weeks in spring. The coastal zone is along the Arctic coastal plain, with elevations lower than 300 m. Coastal zone surface albedo is the highest in winter (>0.8) and the lowest in summer (<0.15). This study suggests that the heat island effect in the vicinity of Barrow, Alaska, is very minimal. Progressive earlier snow cover disappearance at the Barrow National Weather Service station may be an indication of regional spring warming. This study also suggests that snow surface albedo in land surface models should be treated differently for snow at high latitudes as compared with snow in midlatitudes, especially during winter months.