Air temperature distribution and structure of katabatic wind on a shrinking mountain glacier

The glacier katabatic wind system represents a feedback mechanism (de)coupling the glacier and the overlying atmosphere, altering the glacier microclimate.

Still, there are only a limited number of distributed measurements of the atmospheric conditions above the glacier surface. In August 2018, eight weather stations, partly with turbulence measurements at two levels, were installed in the middle and lower part of the Hintereisferner valley glacier in Austria, yielding three weeks of data on the near-surface spatial pattern of atmospheric conditions. These data are used to (a) quantify the observed properties of the glacier wind with regard to its spatial variability, persistence, and the synoptic conditions that erode it and (b) assess how well methods to extrapolate near-surface air temperature over glacier surfaces are influenced by the existence of the glacier wind and match the available observations on Hintereisferner.

 

Despite data limitations and uncertainties, results show that the glacier wind persists under most synoptic conditions, and deepens and speeds up downglacier. However, significant disturbances such as cold front passages and rain events can cause erosion of katabatic wind for periods from minutes to days. Representations of near-surface temperature distribution over the glacier using classical lapse rates and the along flow-line modified Greuell-Böhm model showed variable agreement to the measured data, with evidence for dependency on ambient atmospheric conditions. However, interpretations of the performance of temperature extrapolations should be viewed with caution due to the absence of observations in the upper glacier. We consider how these findings can be included in surface energy balance models of future glacier evolution, and conceptually how this aspect of the glacier microclimate, and the wider valley circulation, can be expected to evolve with continued glacier shrinkage.