Modelling and interpretation of turbulent fluxes in katabatic flows : applications to glaciers and the Greenland ice sheet

Abstract

The aim of this thesis is to improve our understanding of the processes by which heat energy from the atmosphere is transferred through the ABL to glacier surfaces. This is approached from a modelling perspective where appropriate turbulence closure models are developed, interpreted, and applied to both glaciers and the Greenland ice sheet. The first part of this thesis involves the development of such a turbulent closure model which can be used to simulate katabatic flows and the turbulent fluxes associated with them. Knowledge acquired from these simulations is then used to improve the interpretation of meteorological measurements made on glaciers, leading to better estimates of these turbulent fluxes.

The second part of this thesis applies the turbulence closure model to a 3-D boundary layer model of the Greenland ice sheet. This boundary layer model is forced by ECMWF analysis data and simulations are compared to observed meteorological variables of wind, temperature and specific humidity, Experiments with the 3-D model are then carried out to determine the sensitivity of the surface energy flux components to an increase in free atmospheric temperature. The results show that more than half of the increase in the surface energy flux is the result of increases in the turbulent heat fluxes and that albedo feedback can play a significant role in amplifying this increase. In addition, it is pointed out that the climate sensitivity of 2 m temperature is far less than unity as a result of the proximity of the melting ice surface. This is important for other climate sensitivity experiments carried out using 2 m temperature as a forcing parameter.