Abstract
On the Greenland ice sheet, the sensible heat flux is the second largest source of energy for surface melt. Yet in atmospheric models, the surface turbulent heat fluxes are always indirectly estimated using a bulk turbulence parametrization, which needs to be constrained by long-term and continuous observations. Unfortunately, such observations are challenging to obtain in remote polar environments, especially over ablating ice surfaces. We therefore test a classical eddy-covariance method, based on propeller anemometers and thermocouple measurements, to estimate the momentum and sensible heat fluxes on the Greenland ice sheet. To correct for the high-frequency attenuation, we experimentally derive the sensor frequency-response characteristics and evaluate the universal turbulence spectra on the ice sheet. We show that the corrected fluxes are accurate and that the sampling interval can be reduced to 4 s to increase the system’s autonomy. To illustrate its potential, we apply the correction to one year of vertical propeller eddy-covariance measurements in the western ablation area of the ice sheet, and quantify the seasonal variability of the sensible heat flux and of the aerodynamic roughness length.
Highlights
The total mass balance of the Greenland ice sheet, defined as the integrated surface mass balance minus the calving of ice at marine-terminating glaciers, is a primary component of the global sea-level budget
The sensible heat flux is converted to an energy flux according to H = ρaC pw T, where the air density ρa and air heat capacity C p are calculated using the 2-m air temperature, the 2-m air specific humidity and the surface pressure measured by the KNMI at the CESAR tower
This small bias is present when comparing the sensible heat fluxes obtained with the sonic temperature and with the thermocouple attached to the sonic eddy-covariance (SEC) system
Summary
The total mass balance of the Greenland ice sheet, defined as the integrated surface mass balance minus the calving of ice at marine-terminating glaciers, is a primary component of the global sea-level budget. Between 2012 and 2016, the ice sheet lost on average 247 Gt yr−1 of mass (≈ 0.7 mm yr−1 sea-level equivalent), which accounts for 37% of all the land-ice contribution to global sea-level rise (Bamber et al 2018). This recent strong mass imbalance of the ice sheet has been linked to a significant increase in surface melt (Van den Broeke et al 2016), which is either measured in-situ or calculated by closing the surface energy balance,. The sensible heat flux H , is an important source of energy for the melt of seasonal snow in mountain regions (Mott et al 2011) and in the Arctic tundra (Pohl et al 2006), and for the melt of Arctic sea ice (Tjernström et al 2015) and at the surface of Antarctic ice shelves (Kuipers Munneke et al 2018a)
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