The Confluence Zone of the Intense Katabatic Winds at Terra Nova Bay, Antarctica, as Derived From Airborne Sastrugi Surveys and Mesoscale Numerical Modeling

The surface wind field inland of the intense coastal kataba!,•c wind regime at Terra Nova Bay, Antarctica, has been studied both observationally and numerically. Airborne surveys of windinduced features on the snow surface have been used to construct he time-averaged winter surface airflow pattern. The surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution f 32 km. Both methods ofanalys!•s demonstrate that the intense katabatic airstream at Terra Nova Bay is forced by converging air currents in the continental interior. The broadscale confluence zone becomes organized into two regions within about 180 km of the coast. The primary route for katabatic mass transport into the Terra Nova Bay area is Reeves Glacier valley, but an important secondary source is provided by airflow down David Glacier. The former is generated by the Coriolis-induced concentration of mass transport on the left side (looking downwind) of the broadscale confluence zone as well as by the near-coastal mountain deflection of airflow into the valley head. The confluence zone feeding into David Glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet. Source areas for the two airstreams differ with Reeves Glacier valley being fed by cold air formed well into the interior, whereas the airflow down David Glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the Ross Sea. Evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach. Airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow. However, a systematic examination of sastrugi dimensions suggests that such work could also be carried out using SPOT-type satellite observations, which is a more cost-effective approach than aircraft surveying. The double-jet structure of katabatic airflow into the Terra Nova Bay area is well represented by the primitive equation modeling, but much finer grids are needed to resolve the near-coastal drainage details.