Alexandra Weiss

Turbulence Structure and Exchange Processes in an Alpine Valley: The Riviera Project.

During a special observing period (SOP) of the Mesoscale Alpine Programme (MAP), boundary layer processes in highly complex topography were investigated in the Riviera Valley in southern Switzerland. The main focus was on the turbulence structure and turbulent exchange processes near the valley surfaces and free troposphere. Due to the anticipated spatial inhomogeneity, a number of different turbulence probes were deployed on a cross section through the valley. Together with a suite of more conventional instrumentation, to observe mean meteorological structure in the valley, this effort yielded a highly valuable dataset. The latter is presently being exploited to yield insight into the turbulence structure in very complex terrain, and its relation to flow regimes and associated mean flow characteristics. Specific questions, such as a detailed investigation of turbulent exchange processes over complex topography and the validity of surface exchange parameterizations in numerical models for such surfaces, t...

On the effective aerodynamic and scalar roughness length of Weddell Sea ice

We study the effective aerodynamic roughness length z0_eff and scalar roughness length for temperature zT_eff over different compact sea ice types in the Antarctic Weddell Sea by aircraft measurements during two austral summer seasons. z0_eff and zT_eff are highly variable in the Weddell Sea ice area. The averaged value of in all main sea ice areas was smaller than the averaged value of . The ratio between the two roughness lengths was relatively small for new/young sea ice with / ≈ 2, but the ratio became significantly large for the multiyear pack ice with / ≈ 227. For the pack ice area, with sea ice concentration ranging between 95% to 100%, we determined a median = 4.1 × 10−03 m and a median = 1.8 × 10−05 m. In the new, young sea ice area, with sea ice concentration ranging between 98% and 100%, we observed a median = × 10−04 m and a median = 2.2 × 10−04 m. These values of and differ from published observations conducted in a pack ice and new, young sea ice area in the northern hemisphere, such as the Arctic. Most model parameterizations require the roughness lengths as constant values as boundary input parameters. Our study shows that by using the

Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain

\overline{z_{0}\_ {\rm eff}}

Airborne Measurements in the Stable Boundary Layer over the Larsen Ice Shelf, Antarctica

and values of this study, instead of commonly used sea ice roughness length values, the accuracy of parameterized heat and momentum fluxes in the Weddell Sea ice area can significantly be improved.