Ground surface and boundarylayer air temperatures

During this particular winter day, there is a slight increase in the vertical temperature differences on the daily average over the surface for most areas covered by glaciers in the Alps between the perturbed and the control simulations. In the Bernese Alps for example, while there is a slight decrease in the ground surface temperature on average (ATg = -0.24°C and -0.12°C, respectively, for glaciers and transition zone), but there is a similar decrease in the boundary layer air temperature The stronger tempera ture drop tends to be associated with locations where there is less snow accumulating over glaciers and over the transition zone as well as land cover compared to the control simulation. Elsewhere in the region surrounding the glaciers, it may happen that surface temperature increases slightly. Generally, where there is "bare" glacier or where snow mass is below 10 g kg"', surface temperature tends to decrease. Figure 3c shows the differences in air and ground temperatures between the control and the perturbed simulations in the Bernese Alps over the glacier and transition zone during February 27, 1990. In both simulations, the ground surface temperature stays below freezing. It is colder over the glacier on average but it is warmer during night and colder during the day in the transition zone, compared to the control simulation. The surface air temperature is colder on the average and the resulting difference between ground and surface air temperature increases slightly on average during this day.

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