THE INFLUENCE OF STRATIFICATION ON HEAT AND MOMENTUM TURBULENT TRANSFER IN ANTARCTICA

Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes (u'w'BAR, v'w'BAR and theta'w'BAR) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri. the friction velocity (u*) and the eddy diffusivities for heat (K(h)) and momentum (K(m)). The results show a big dependence of stability on K(m), K(h) and u*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K(h)/K(m)) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed.