EGU2020-15227, updated on 13 Mar 2023
EGU General Assembly 2020
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Contribution of turbulent heat fluxes to surface ablation on the Greenland ice sheet.

Maurice Van Tiggelen1, Paul Smeets1, Carleen Reijmer1, Brice Noël1, Jakob Steiner2, Emile Nieuwstraten2, Walter Immerzeel2, and Michiel van den Broeke1
Maurice Van Tiggelen et al.
  • 1Utrecht University, Institute for Marine and Atmospheric Research, Utrecht, Netherlands (
  • 2Utrecht University, Department of Physical Geography, Utrecht, Netherlands

Over ice sheets and glaciers, the turbulent heat fluxes are, next to the radiative fluxes, the second largest source of energy driving the ablation. In general, most (climate) models use a bulk turbulence parametrization for the estimation of these energy fluxes. Recent work suggest that the turbulent heat fluxes might be greatly underestimated by such models. Unfortunately, only a few direct and long-term observations of turbulent fluxes are available over ice sheets to evaluate their inclusion in models. 

In this study, we developed a vertical propeller eddy-covariance method to continuously monitor the sensible heat fluxes over the Greenland ice sheet (GrIS). We quantify its contribution to surface ablation using three years of data from the K-transect, located in the western ablation area of the GrIS. The direct flux measurements are also compared to those from several bulk turbulence models, and to a high-resolution regional climate model (RACMO2), in order to quantify modelling uncertainty.

The differences between observations and models highlight the need for upgrading the bulk turbulence parameterizations and especially the model parameters, such as the surface roughness lengths. We also find that during short but extreme warm events, the turbulent heat fluxes become the largest source for surface ablation. Typical for such intense events on the K-transect are fast changes in wind direction, which cause changes in the surface roughness parameters due to the anisotropic feature of the ice hummocks. These parameters are critical for modelling the turbulent fluxes in bulk parameterizations, but are often variable and unknown. We conclude with drone topography measurements to better constrain the surface roughness locally, and discuss methods to improve the modelling of turbulent surface fluxes on the whole GrIS.

How to cite: Van Tiggelen, M., Smeets, P., Reijmer, C., Noël, B., Steiner, J., Nieuwstraten, E., Immerzeel, W., and van den Broeke, M.: Contribution of turbulent heat fluxes to surface ablation on the Greenland ice sheet., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15227,, 2020.


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