Characteristics of turbulence in the lower atmosphere at Halley IV station, Antarctica

Abstract

Abstract A study of turbulent processes taking place in the stably stratified boundary layer overlying an Antarctic ice-shelf is presented. The ice-shelf is regarded as a flat, homogeneous surface. Turbulent measurements were made by the British Antarctic Survey from their meteorological station at Halley, Antarctica. Instrumentation included a 32 m mast supporting three ultrasonic thermo-anemometers, platinum resistance thermometers and other meteorological instruments. Mechanical and thermal properties of boundary layer turbulence are investigated, and parameters such as friction velocity and turbulent exchange coefficients are calculated and their dependence on the gradient Richardson number and local stability parameter, z / Λ , is discussed. It is shown that the friction velocity is a key parameter controlling the turbulent characteristics in this particular boundary layer. Strong surface-based thermal inversions of up to 10°C over the lowest 30 m are often observed. The relationships between the inversion strength and turbulent parameters are studied and their influence on near-surface mixing is assessed. It is shown that in the very strongly stratified boundary layer stability functions for heat and momentum may reach a constant value at fairly low-levels, suggesting that z -less scalings are applicable under such conditions. The implications for numerical modelling of the stable boundary layer are discussed and the need for further observational studies is highlighted.