This work constitutes the inaugural dissertation for the author’s degree of Doctor of Philosophy presented to the Faculty of Science of Stockholm University. The investigations discussed may be considered a link in the chain of extensive glaciological research work carried on in Scandinavia, Iceland, Spitsbergen and Greenland under the leadership or by the initiative of Professor Hans W:son Ahlmann. Ahlmann’s interest has come to be more and more concentrated upon the relationship between the material balance (regime) of glaciers and the corresponding meteorological factors. Wallén’s work is particularly concerned with the relationship between ablation and climatic condition. It is closely related to the pioneer work on the importance of convection and condensation in the ablation process carried out by Sverdrup and Ahlmann in Spitsbergen in 1934. He has studied in detail the distribution of wind velocity, temperature and humidity in the air stream above the glacier surface and also the insolation conditions. He has thus been able to determine quantitatively, with a considerable degree of accuracy, the heat balance on the glacier surface.
The Kårsa Glacier is a small valley glacier, only 2 km.2 in area, situated in Swedish Lapland cluse to the Norwegian border in 68° N. and 18° E. Its height above sea level is between 800 and 1500 m.
The author first gives a comparative analysis of the climatological conditions on the glacier and at two adjacent meteorological stations. The insolation conditions are of particular interest. Especially when the sky was overcast the insolation was considerably greater on the glacier than down at Abisko at 380 m. The author explains this as being due to the reflection between the glacier surface on the one hand and the atmosphere and the clouds on the other. Wallén considers it important that the glacier is situated at a higher elevation than the meteorological station and does not accept the view that the clouds in the Scandinavian mountains are probably thinner than is generally the case in the temperate zone.
The annual accumulation over the whole glacier averaged 3.70 million cubic metres of water and the ablation 3.93 million cubic metres. The difference, 0.23 million cubic metres, represents the annual loss of material. This figure is smaller than those obtained by Ahlmann, Lindblad and Schytt for the mean annual shrinkage of the Kåtrsa Glacier during earlier decades. The reviewer feels bound to express his view that unavoidable sources of error have contributed towards too low a value. The order of magnitude of the shrinkage of the Scandinavian glaciers during recent years has been 0.5–1.0 million cubic metres of water per square kilometre per annum, while Wallén’s result gives only 0.1 million cubic metres per square kilometre for the Kårsa Glacier. The climate seems, however, to have been slightly less favourable for the shrinkage of the glacier during Wallén’s years of investigation than during previous years.
Except by insolation and convectional heat transport through the air ablation occurs by condensation of humidity on the cold glacier surface. The vapour pressure in the air during the ablation season is generally higher than the maximum vapour tension at the surface, so that condensation of water vapour on the glacier is more common than evaporation; during the spring however the position can, on occasions, be reversed. According to Wallén 60 per cent of the ablation is due to insolation, 30 per cent to convection and 10 per cent to condensational heating. The insolation was of far less importance on the glaciers studied by Ahlmann in Spitsbergen, Iceland and Greenland, being 10 per cent in the latter and about 30 per cent in the two former regions. It must be remembered, however, that Ahlmann’s investigations only covered short periods of the ablation season, whereas Wallén’s refer to the whole season. The heat supply from the air is of slightly less importance than the insolation on the Kårsa Glacier, partly because this glacier is situated so high that the air temperature is always rather low, partly because it is influenced by two different types of air masses, both supplying small amounts of convectional heat. These two types consist on the one hand of continental warm air from the east with a clear sky and high temperature but with weak winds reducing the heating power, and, on the other, maritime cold air with cloudy skies and strong winds but with low temperature. In spite of the fact that the insolation is quantitatively of a greater importance than the convectional and condensational factors it has been the change of the two latter factors which has resulted in the shrinkage of the glacier. Wallén shows that the meteorological causes for the shrinkage have been increased temperature during the summer and, particularly in July, increased humidity and a prolonged ablation season.
WaIlén’s investigations have been criticized so far as the theoretical chapter on convection is concerned, but the agreement between calculated and observed values is so good that one must admit that the results support his assumptions. Wallén’s investigations represent a most valuable complement to, and development of, the pioneer works on the importance of meteorological factors in the ablation process initiated by Ahlmann and Sverdrup. It is highly desirable that such investigations should be undertaken on other glaciers, particularly on those to which other climatic conditions apply. In addition to the meteorological and glaciological knowledge resulting from such investigations, they will help us to understand climatic variations as a whole and in the long run probably also the causes of ice ages.
