A Vertical Propeller Eddy-Covariance Method and Its Application to Long-term Monitoring of Surface Turbulent Fluxes on the Greenland Ice Sheet

摘要

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.