E l e c t r o n i c   r e p r i n t


HYDRAULIC GEOMETRY
OF A SUPRAGLACIAL STREAM,

RAGNARBREEN, SPITSBERGEN

Andrzej Kostrzewski and Zbigniew Zwolinski

WEATHER CONDITIONS

West Spitsbergen lies in the zone of subpolar maritime climate (Martyn 1985), which is influenced by the North Atlantic Drift. A full picture of meteorological issues at Skottehytta in the period from 28 June to 26 July 1985 has been presented in a separate paper by Kostrzewski et al. (1989). It shows that the summer of that year was exceptionally warm: its probability of occurrence is once in 10 years. This observation emphasises the climatic contrast between the central part of West Spitsbergen and its western and southern coasts: the fiord area of the interior shows a high degree of continentality. The mean air temperature of the observation period amounted to 8.4 °C, while the rainfall equalled 10.1 mm.

The mean daily temperature on 24 July was 10.5 °C, and the diurnal variation was low (9-12 °C) (Fig. 2a). On the preceding day, the highest mean diurnal temperature (12.9 °C) and variation (9.8-16.8 °C) were recorded. Relative humidity amounted to 76%, vapour pressure to 9.5 hPa, and saturation deficit to 3.1 hPa, which was connected with the advection of warm air. There was no rain on that day, as opposed to 21 and 22 July (2.6 and 7.5 mm, respectively). There was also no wind on the day when measurements of the supraglacial stream were carried out, but on 20-22 July winds from the southerly quarter (from the Billefjorden direction) were recorded, blowing with an average speed of 2.3 m s-1 (1.0-3.7 m s-1). Cloudiness was defined as 5; similar values (4-6) were observed on the four preceding days (Fig. 2a). Total and diffuse radiation was 189 W m-2 at 13:00, while at 7:00 the respective figures were 389.3 and 33.4 W m-2 (Fig. 2b).


Fig. 2. Temperature, cloudiness, and total and diffuse radiation from 21 to 24 July 1985 at the Skottehytta meteorological station, Petuniabukta, Billefjorden, Spitsbergen


Summing up the meteorological conditions obtaining on the day of the supraglacial stream measurements, they must be described as typical of the ablation season in this climatic zone. No extraordinary weather phenomena occurred that might influence the character of water flow in the supraglacial stream, except for a higher temperature the day before. Considering, however, that the delay in flow response of the Ebbaelva in its segment reaching the bay ranges from 6 to 10 hours (Kostrzewski et al. 1989), it might be assumed that for supraglacial streams the response time is much shorter. Hence, the measurements of the Ragnarbreen supraglacial stream took place after the higher wave caused by the increased temperature on 23 July had already passed. Moreover, the radiation balance on the morning of 24 July was variable, which did not significantly affect the stream discharge given the high albedo of the glacier surface.

The supraglacial stream under study was only supplied by glacier surface ablation following the rhythm of diurnal changes in air temperature and radiation observed in the period preceding the measurements. In the stream catchment no snow patches were found, and rainwater had already left its area (Kostrzewski et al. 1989). Thus, the water supply and flow of the stream occurred under a glacial (ablation) regime.