Surface albedo in Ny-Alesund, Svalbard: variability and trends during 1981-1997

Since 1981, hourly values of albedo have been measured routinely at Norwegian Polar Institute's research station in Ny-Alesund, Svalbard, We have undertaken statistical analysis of the time series 1981-1997 to investigate potential long-term variability and trends in the albedo data set. The following questions have been raised and answered by regression analysis: (i) Has the time of beginning of snow melt changed? (ii) Have melt rates changed? (iii) Has the time of snow arrival in fall changed? (iv) Has the period without snow cover changed? The period without snow on the ground is studied because of its importance for tundra characteristics as a habitat for biota, e.g. length of the growth season. Our data show that albedo varies seasonally, with large variations in spring and autumn and much smaller variations in winter and summer. The variability is reasonably constant within each season. Density estimates of the albedo data suggest that the dates with highest likelihood for (i) start of snow melt and (ii) start of snow formation are 5th of June and 17th of September, respectively. Highest probability for the length of snow-free season is 94 days. None of the tests indicated any significant trends (or indications of climate change) in the 17-year record of albedo, that means that the four questions above were all answered by "no." Correlation with the North Atlantic Oscillation (NAO) index is also investigated. No correlation between the NAO index and albedo nor temperature or precipitation was found. Even so, because of the short duration that our data set spans, we cannot rule out that such a correlation exists on decadal time scales. (C) 2002 Elsevier Science B.V. All rights reserved.