Jökull


Jökull - 01.12.1972, Síða 60

Jökull - 01.12.1972, Síða 60
on the infiltration and percolation of water in- to glaciers and the movement of water inside a glacier in the unsaturated and saturated zones. Besides, it is essential to develop techniques to obtain accurate measúrements of input of meltwater and rain to the glacier and of the changes of the liquid water storage underneath the summer surface. CONCLUSION As concluded by Have?is, Miiller and Wil- mot (1965) the use of logarithmic profiles for wind speed, temperature and vapor pressure is preferable to earlier methods used in computa- tion of the turbulent heat fluxes which suffered from the doubtful assumption that observed ablation could be used for calculating the co- efficients of diffusivity. On Bægisárjökull still better results were obtained by using loga- rithmic-plus-linear profiles rather than using logarithmic. It appeared necessary to make al- lowance for the suppressing of the turbulence under the stable conditions present. The un- defined experimental conditions on the mete- orological site however devaluated the general validity of this result. Uncertainties in daily values for computed energy balance components as well as measured ablation restrict the value of the energy budget computation to give only general trends and relative importance of the processes for longer periods. The same is valid in general, for the computed meltwater. The results from Bægisárjökull reveal a sea- sonal trend to increased importance of the tur- bulent energy fluxes throughout the summer. The great importance of the general air circula- tion was also illustrated. During the summer of 1967 which had frequent cold northerly winds, the turbulent processes were reduced and tlie net radiation was responsible for the greatest part of the relatively small ablation, in spite of relatively high albedo comparecl with the summer of 1968. Bægisárjökull has a mere existence, protectecl by the surrounding mountains (Björnsson 1971). The proximity of the northern coast of Iceland is also important for its life. Northerly winds from the sea bring accumulation during the 58 JÖKULL 22. ÁR winter and reduce ablation during the summer. Further the glacier faces to north and obtains during the summer only about 84 percent of the insolation on a horizontal surface. Souther- ly winds bring also a good deal winter ac- cumulation but the highest rates of ablation are accompanied with winds from these direct- tions, mainly because the turbulent processes are accentuated. ACKNOWLEDGEMENTS Instruments were ?nade available by the I?i- stitute of Geophysics and Institute of Geo- graphy both at Oslo University, Norwegia?i Meteorological Institute, Oslo, Norwegia?i Polar Institute, Oslo, a?id in Iceland by the National Energy Autliority and Vedurstofan (Meteoro- logical Service). Financial support was given fro?n the Science Foundation, Iceland. Personal thanks are due to Olav Liestf>l, Sig- urjón Rist, Sigurdur Thorarinsson and last but not least to my companion on the glacier Jó- hann Sigurjónsson. REFEREN CES Ahlrnann, H. W. and Thorarinsson, S. 1943: Vatnajökull. Scientific results of the Swed- ish-Icelandic Investigations 1936—37—38. Reprints from Geografiska Annaler 1937— 1940, 1943. Stockholm. Björnsson, Helgi. 1971: Bægisárjökull, North- Iceland. Results of glaciological investiga- tions 1967—1968. Part I. Mass balance and general meteorology. Jökull 21: 1—23. Calder, K. L. 1966: Concerning the similaritv theory of Monin/Obukhov. Quart. J. Roy. Meteorol. Soc. 92, 141—146. Cramer, H. E. 1967: Turbulent Transfer Pro- cesses for Quasi-Homogeneous FIows within the Atmosplieric Surface Layer. The Physics of Fluids Supplements. Am. Inst. of Phys- ics, New York, p. 240—246. Dyer, A. J. 1963: The adjustment of profiles and eddy fluxes. Quart. J. Roy. Meteorol. Soc. 89, 276-280.
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