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

A study of turbulent processes taking place in the stably stratified bounda ry layer overlying an Antarctic ice-shelf is presented. The ice-shelf is re garded as a flat, homogeneous surface. Turbulent measurements were made by the British Antarctic Survey from their meteorological station at Halley, A ntarctica. Instrumentation included a 32 m mast supporting three ultrasonic thermo-anemometers, platinum resistance thermometers and other meteorologi cal instruments. Mechanical and thermal properties of boundary layer turbul ence are investigated, and parameters such as friction velocity and turbule nt exchange coefficients are calculated and their dependence on the gradien t Richardson number and local stability parameter, z/Lambda, is discussed. It is shown that the friction velocity is a key parameter controlling the t urbulent characteristics in this particular boundary layer. Strong surface- based thermal inversions of up to 10 degreesC over the lowest 30 m are ofte n observed. The relationships between the inversion strength and turbulent parameters are studied and their influence on near-surface mixing is assess ed. It is shown that in the very strongly stratified boundary layer stabili ty functions for heat and momentum may reach a constant value at fairly low -levels,suggesting that z-less scalings are applicable under such condition s. The implications for numerical modelling of the stable boundary layer ar e discussed and the need for further observational studies is highlighted. (C) 2001 Elsevier Science B.V. All rights reserved.