Master thesis defence by Signe Hillerup Larsen – Niels Bohr Institute - University of Copenhagen

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Master thesis defence by Signe Hillerup Larsen

Surface mass and energy balance at A.P. Olsen Ice Cap (NE Greenland)

- from observations and modelling

The distributed surface mass and energy balance are calculated on A.P. Olsen Ice Cap in Northeast Greenland (74°38' N, 21\°26' W), using two different models. Data from the GlacioBasis monitoring programme provide observations from the ice cap from three automatic weather stations (AWS) and 15 stakes since 2008. An AWS in the valley 35km southeast of the glacier (44 masl) is used for extending the temperature and precipitation record from the glacier back to 1995. A second AWS on a mountain top (1283masl) 20 km east of the glacier is used to investigate the effect of temperature inversion layer formation on temperature upscaling. A temperature index melt model, driven by the 16 year long temperature and the precipitation record, is showing a decreasing trend in surface mass balance between 1995 and 2011. In this period the three most negative years are 2007 (bn=-0.69 m/yr), 2009 (bn=-0.42 m/yr) and 2011 (bn=-0.32 m/yr) and the most positive year is 1998 (bn=0.24 m/yr). The temperature inversion layer formations are accounted for using monthly mean lapse rates calculated for the longest possible period of observational data at the glacier, and any inter annual variability in inversion depth and strength will act as an error source for temperature upscaling and thereby melt modelling. From ground penetrating radar measurements the snow distribution is showing a nonlinear trend with elevation across the ice cap. The distributed energy balance model by Hock and Holmgren (2005) is set up using the AWS data from the glacier producing distributed energy balance grids for 2009, 2010 and 2011. Net radiative fluxes are seen to be the main contributor to surface melt and shadows are shown to have a large effect on the melt. Both models are showing a high sensitivity to snow depth distribution across the ice cap. Experiments on the surface mass balance sensitivity to climate change show that the predicted increase in summer temperature of 2-6° C (Christensen et al. 2007)} cannot be balanced by the predicted increase of precipitation of 40 %. 

Christine Hvidberg, Centre for Ice and Climate
Michele Citterio, GEUS