Abstract
Abstract. We compare 5 years of meteorological records from automatic weather stations (AWSs) on Storbreen and Midtdalsbreen, two glaciers in southern Norway, located approximately 120 km apart. The records are obtained from identical AWSs with an altitude difference of 120 m and cover the period September 2001 to September 2006. Air temperature at the AWS locations is found to be highly correlated, even with the seasonal cycle removed. The most striking difference between the two sites is the difference in wind climate. Midtdalsbreen is much more under influence of the large-scale circulation with wind speeds on average a factor 1.75 higher. On Storbreen, weaker katabatic winds are dominant. The main melt season is from May to September at both locations. During the melt season, incoming and net solar radiation are larger on Midtdalsbreen, whereas incoming and net longwave radiation are larger on Storbreen, primarily caused by thicker clouds on the latter. The turbulent fluxes are a factor 1.7 larger on Midtdalsbreen, mainly due to the higher wind speeds. Inter-daily fluctuations in the surface energy fluxes are very similar at the AWS sites. On average, melt energy is a factor 1.3 larger on Midtdalsbreen, a result of both larger net radiation and larger turbulent fluxes. The relative contribution of net radiation to surface melt is larger on Storbreen (76%) than on Midtdalsbreen (66%). As winter snow depth at the two locations is comparable in most years, the larger amount of melt energy results in an earlier disappearance of the snowpack on Midtdalsbreen and 70% more ice melt than on Storbreen. We compare the relative and absolute values of the energy fluxes on Storbreen and Midtdalsbreen with reported values for glaciers at similar latitudes. Furthermore, a comparison is made with meteorological variables measured at two nearby weather stations, showing that on-site measurements are essential for an accurate calculation of the surface energy balance and melt rate.
Highlights
The climate in southern Norway shows a strong precipitation gradient from west to east, with a maritime climate at the western coast and a more continental climate east of the main watershed, located less than 150 km from the coast (Fig. 1, Green and Harding, 1980)
The glaciers of southern Norway are found in the areas with the largest annual snow amount; areas characterized by a combination of low temperatures due to topography and sufficient precipitation (Figs. 1 and 2)
– Air temperature was corrected for radiation errors at times when the sensor was not aspirated using expressions that give the excess temperature as a function of wind speed and the sum of incoming and reflected solar radiation
Summary
The climate in southern Norway shows a strong precipitation gradient from west to east, with a maritime climate at the western coast and a more continental climate east of the main watershed, located less than 150 km from the coast (Fig. 1, Green and Harding, 1980). The glaciers of southern Norway are found in the areas with the largest annual snow amount; areas characterized by a combination of low temperatures due to topography and sufficient precipitation The annual mass balance turnover (the summed absolute values of the area-averaged winter and summer balance divided by two) on glaciers in southern Norway reflects the precipitation gradient, ranging from 3.7 m water equivalent (w.e.) at Alfotbreen near the coast to 0.92 m w.e. on Grasubreen in eastern Jotunheimen, further inland. On Alfotbreen, interannual fluctuations in the net mass balance are primarily determined by variations in the winter balance, while summer-balance variations dominate interannual variability at the more continental glaciers (Andreassen et al, 2005). Climate maps reveal large-scale patterns in meteorological variables, giving a first indication where conditions are favourable for glaciers. Accumulation and ablation on glaciers are related to the local air temperature and winter precipitation, but are influenced by other
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