INTRODUCTION: For many years, frictional meltwater was the assumed explanation for the low friction on snow. Some experiments have been conducted to verify the presence of a meltwater film 1-3, but the results were inconsistent. The goal of the present study was to shed more light on the potential generation of frictional meltwater. METHODS: The friction coefficient of an XC ski was measured on a linear snow tribometer 4 at speeds between 5 and 25 m/s and at a snow temperature of -3.6°C. During the measurements, an infrared camera filmed a segment of the sliding track of 0.15 m length. From the infrared images, we calculated the course of the hottest snow spots after the passage of the ski 5. RESULTS: The maximum temperature of the hottest spots after the passage of the ski was -0.09°C (at 25 m/s). The subsequent course of the temperature is shown in Fig. 1. Whilst at low speed the decrease was exponential from the beginning, at 15 m/s and, more pronouncedly, at 25 m/s the initial temperature decrease was relatively flat and linear and changed to an exponential decrease only later on. DISCUSSION/CONCLUSION: If the snow surface temperature would decrease solely due to energy transfer by radiation, conduction and convection, an exponential decrease immediately after the passage of the ski would be expected. The cause for the initial linear part of the temperature curve must be based on an additional mechanism overlapping the cooling. This mechanism only seems relevant at higher speed: a phase change of refreezing frictional meltwater on the hottest spots.
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