Suitability of a constant air temperature lapse rate over an Alpine glacier: testing the Greuell and Böhm model as an alternative

Near-surface air temperature, typically measured at a height of 2 m, is the most important control on the energy exchange and the melt rate at a snow or ice surface. It is distributed in a simplistic manner in most glacier melt models by using constant linear lapse rates, which poorly represent the actual spatial and temporal variability of air temperature. In this paper, we test a simple thermodynamic model proposed by Greuell and Böhm in 1998 as an alternative, using a new dataset of air temperature measurements from along the flowline of Haut Glacier d'Arolla, Switzerland. The unmodified model performs little better than assuming a constant linear lapse rate. When modified to allow the ratio of the boundary layer height to the bulk heat transfer coefficient to vary along the flowline, the model matches measured air temperatures better, and a further reduction of the root-mean-square error is obtained, although there is still considerable scope for improvement. The modified model is shown to perform best under conditions favourable to the development of katabatic winds – few clouds, positive ambient air temperature, limited influence of synoptic or valley winds and a long fetch – but its performance is poor under cloudy conditions

Warming trends in Permafrost and thermo-insulation effect of a seasonal snow-cover on permafrost soil in Bayelva, Svalbard (1998 - 2017)

Permafrost around the Arctic is warming and thawing. We report data from the high arctic research site Bayelva (78.551N; 11.571E) located close to Ny-Alesund. Data on meteorology, energy balance components and subsur- face observations have been made for the last 20 years (1998-2017; Boike et al. 2017). This study site is underlain by permafrost with current mean permafrost temperature of -2.8◦C and is seasonally snow-covered from October to May. Mean annual, summer and winter soil temperature data at all depths have beenrising over the period of record with a warming trend of 0.18±0.07◦C/year in active layer and top of permafrost. However, interannual to sub-decadal variability is evident in the data and results mostly from differences of theclimate during the winter months. The modeled active layer thickness using the Stefan equation has increasedcontinuously from about 1m in 1998 and is estimated to have surpassed 2 m in 2016. The data show that snow ablation has started earlier, thus extending the snow free season, potentially re-sulting in more time for soil warming and deepening of active layer. The snow cover onset and ablation, aswell as the thermo insulation properties of the snow cover, will be investigated together with active layer and permafrost variables (temperature, volumetric water content) for further understanding of the observed warming and deepening. Boike, J., Juszak, I., Lange, S., Chadburn, S., Burke, E., Overduin, P. P., Roth, K., Ippisch, O., Bornemann, N., Stern, L., Gouttevin, I., Hauber, E., and Westermann, S.: A 20-year record (1998–2017) of permafrost, active layer and meteorological conditions at a high Arctic permafrost research site (Bayelva, Spitsbergen), Earth Syst. Sci. Data, 10, 355-390, https://doi.org/10.5194/essd-10-355-2018, 2018