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Antarctic
Research
Summary
of project
Personnel
Collaborators
Publications
(since 1998) and completed manuscripts
Publication
for 1997 and before
Photos
Maps
Field
work 1999/2000
Field
work 2000/2001
Ongoing
scientific work
Katabatic Winds in Eastern Antarctica and their Interactions with Sea Ice
An international (U.S.-French-Australian) katabatic wind study is presently underway in East Antarctica. We pro-pose to continue this study, with a broaden-ing of the research objectives. New and exciting data sets are available and allow us to investigate the interaction of the katabatic wind and the sea ice to an extent not previously possible.There are two arrays of Automatic Weather Stations (AWS) in Eastern Antarctica, one stretching from Dome C (3280 m) to the coast close to Dumont d'Urville, the other along the coast from Dumont d'Urville to Cape Webb. The latter one includes Cape Denison and Port Martin, infamous for the extremely high wind speeds which are the strongest winds found anywhere close to sea level on Earth. 1995 was the first year for which, with the aid of a new wind sensor, year-round observations of the wind velocity were obtained at Cape Denison. A new record in the mean monthly wind speed of 27.7 m/s was observed, indicating that the correction carried out on the original data set from Mawson's expedition, reduced the wind speeds by too much, a fact Loewe (1956) already suggested. These winds are of katabatic nature and can drive the ice from the coast even in midwinter. Up until now, these events were difficult to examine, as traditional satellite imagery was either limited by darkness (visible), the presence of clouds (thermal IR) or resolution (passive microwave). The active microwave (SAR) images from several satellites are being processed in Fairbanks, the only SAR receiving station in the USA. We have started to study the formation, size, and persistence of polynyas as function of the very strong observed winds and with the help of a Russian model, which we modified (Wendler et al. 1997). However, only limited SAR images were available for the above study, but we have ordered additional images to obtain a better insight in the processes. Polynyas also have important implications for both the local and global climate, as open water releases about two orders of magnitude more energy in winter than the ice covered ocean. Polynyas and open water thus affect the heat transfer from the ocean to the atmosphere, as well as the production of sea ice and cold, saline Antarctic Bot-tom Water. Concerning remote sensing and sea ice, the expertise of ICAIR (Christchurch, New Zealand), where the P.I. will spend the austral summer 1997/98, will add value to the study and will broaden international cooperation. One new AWS station is proposed to be established a short distant inland (15km) from Cape Denison, where new maxima in wind speed are predicted by model calculations, and the station of Cape Webb to the east to investigate the coastal polynyas over a larger coastal area.
Besides the interaction between the katabatic wind and the sea ice, modeling efforts will be continued. Our French collaborators (Pettré and Gallé) have developed a new mesoscale model, which is running in near real time at Dumont d'Urville. Further, the joint work with the University of Wyoming (T. Parish) will be continued. In addition, a new, more detailed elevation terrain map will be incorporated into the model. The general picture between observations and models is in fairly good agreement, however improvements, for both the mean conditions and for the sudden onset and cessation of the katabatic flow should be obtained.
The Australian AWS net is to the west of our stations, and further West the Japanese carry out AWS measurements. Together, these stations will enable us to study not only the climatology of Eastern Antarctica in detail, but also the influence of cyclonic sys-tems on the gravitational flow with this substantial coverage.
