Numerical simulations and analytical estimates of katabatic flow over a melting outflow glacier
2006 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 120, no 3, 509-534 p.Article in journal (Refereed) Published
A realistic simulation of katabatic flows is not a straightforward task for numerical models. One complicating factor is that katabatic flows develop within a stably stratified boundary layer, which is poorly resolved and described in many numerical models. To capture the jet-shaped shallow flow a model set-up with high vertical resolution is also required. In this study, ‘a state of the art’ mesoscale numerical model is applied in a simulation of katabatic flow over a melting glacier. A basic agreement between observations and model results is found. From scale analysis, it is concluded that the simulated flow can be classified as katabatic. Although the background flow varies in strength and direction, the simulated katabatic flow over Breidamerkurjökull is persistent. Two factors vital for this persistence are identified. First, the melting snow maintains the surface temperature close to 0 °C while the air temperature warms adiabatically as it descends the slope. This provides a ‘self enhanced’ negative buoyancy that drives the flow to a balance with local friction. Second, the jet-like shape of the resulting flow gives rise to a large ‘curvature term’ in the Scorer parameter, which becomes negative in the upper jet. This prevents vertical wave propagation and isolates the katabatic layer of the influence from the free troposphere aloft. Our results suggest that the formation of local microclimates dominated by katabatic flow is a general feature over melting glaciers. The modelled turbulence structure illustrates the importance of non-local processes. Neglecting the vertical transport of turbulence in katabatic flows is not a valid assumption. It is also found that the local friction velocity remains larger than zero through the katabatic jet, due to directional shear where the scalar wind speed approaches its maximum.
Place, publisher, year, edition, pages
2006. Vol. 120, no 3, 509-534 p.
Glacier, Katabatic flow, Non-local transport, Scorer parameter, Stable boundary layer
Meteorology and Atmospheric Sciences
IdentifiersURN: urn:nbn:se:su:diva-24002DOI: 10.1007/s10546-006-9059-3OAI: oai:DiVA.org:su-24002DiVA: diva2:196309