Refreezing of frictional meltwater behind a sliding ski

Low friction on snow has been attributed to the formation of a frictional meltwater layer for many years, yet experimental evidence for this mechanism has remained inconsistent. In a large-scale snow tribometer lab, we measured the snow surface temperature behind a sliding cross-country ski and a flat sliding sample with an infrared camera to study the meltwater film at realistic skiing conditions. At speeds ranging from 5 to 25 m/s and an initial snow temperature of −3.5 °C, surface temperatures increased locally to as high as −0.09 °C. At 15 and 25 m/s, the temperature decay following a ski passage deviated notably from the expected exponential cooling behavior. Instead, the post-passage temperature profile exhibited two distinct phases: an initial slow decline, attributed to latent heat release during the freezing of meltwater, followed by a phase of exponential cooling. This two-phase behavior provides clear evidence for the presence of frictionally generated meltwater. Although the presence of meltwater was most clearly observed after repeated passes over the same track and only at the higher speed, its presence at lower speed or during initial runs cannot be ruled out. The infrared system monitored only the exposed snow surface and may have missed transient meltwater that refroze beneath the ski.