The 5th Conference on Polar Meteorology and Oceanography

J8.6
INVESTIGATIONS FOR DETERMINATION AND PARAMETERIZATION OF TURBULENT FLUXES IN THE ARCTIC

Michael Hofmann, University of Hannover, Hannover, Niedersachsen, Germany; and R. Roth

With the helicopter-borne turbulence measurement system HELIPOD there have been made two measurement campaigns in the Arctic in the years of 1995 and 1996. Measurement flights were conducted from board RV POLARSTERN. The aim of these measurements was to gather near surface turbulent fluxes under different boundary conditions, like for example different stratification or different surface roughness.

The meteorolocigal conditions during those measurements were characterised by low wind velocities and small temperature differences between ice and atmosphere. Moreover, the ice concentration in the flight areas was nearly 100 percent and the stratification of the boundary layer was almost always stable. Thus, the absolute values of the turbulent fluxes were small, as expected.

We investigated if the HELIPOD sonde might be suitable to improve turbulence parameterizations via improved turbulence measurements. The idea is as follows. The data we used have a considerable smaller turbulence signal than data used by other groups for turbulence parameterization investigations. Thus, if we are able to confirm existing parameterizations with our data despite of the weak turbulence and with less or equal error values, then the accuracy of the HELIPOD sonde is suitable for improved turbulence measurements.

Two turbulence parameterizations are compared with measurement results. Firstly, there is the bulk parameterization for the surface layer and secondly, there is the local scaling concept for the stable boundary layer. It is shown, that there is no contradiction between our measurements and the bulk concept. In any case, it is a progress in boundary layer turbulence measurements to compare theory with data from airborne measurements gathered directly at 10 m height. Thus, no extrapolation down to the usual reference level of the bulk parameterization was necessary. Also the concept of local scaling for the stable boundary layer is confirmed by our measurements with errors less or equal to previous measurements by other authors.

All in all, with HELIPOD measurements in several heights ranging from 10 m up to the boundary layer top we confirmed existing turbulence parameterizations despite of the considerable weak turbulence signal.

The 5th Conference on Polar Meteorology and Oceanography