The structural basement of Alexander Island consists of a wide belt of accretionary complex rocks, the LeMay Group (Bum 1984). This is overlain by ?Cretaceous-Tertiary calcalkalinevolcanic rocks (Bum 1981), and intruded by several slightly younger, but related, plutons (Care 1983). The Rouen Mountains batholith is a large group of these plutons which occurs in the northern part of the island.

The records obtained from a monostatic acoustic sounder run at Halley, Antarctica, have been analysed with the use of data from instruments on a 32 m mast and from radiosonde ascents. Echoes representing ground-based layers, waves, and shallow gravity currents are discussed. The spiky ground-based echo is related to a westerly surface wind, whilst a layered wavy flow is related to surface easterlies. Such relationships are consistent with the sloped inversion wind regime at Halley.

An Ekman analysis of the surface drainage winds over a sloping ice surface is reported. Ekman pumping by the boundary layer leads to the formation of an upper tropospheric cyclonic vortex above the summit of the ice sheet. The strength and distribution of upper level vorticity is determined by the shape of the underlying ice sheet. The calculation is verified by comparison with the results from a multi-level primitive equation model of flow above an axisymmetric ice sheet. Both models predict that the surface drainage flow will die out on a timescale of a few days, while the upper vortex is predicted to be considerably stronger than observed. Various mechanisms which could lead to the depletion of upper level vorticity, and hence to the retention of a substantial drainage flow, are discussed. It is concluded that disruption of the polar vortex by decaying mid-latitude cyclones, and the consequent export of cyclonic vorticity to lower latitudes, is the most probable mechanism.

Analysis of high-resolution data from slow-ascent radiosondes released at Halley station, Antarctica (75°38′S, 26°40′W), shows that internal gravity wave phenomena are frequently present in the lower troposphere. There is a strong tendency for these waves to induce a vertical transport of the SE-NW component of momentum, this being the component perpendicular to the alignment of regular ridges in the ice shelf on which the base is built and is independent of the mean wind direction. A method for estimating the variation of the momentum fluxes with height is described. Results show that momentum flux divergences equivalent to accelerations of about 10 ms−1 per day are common at Halley.

Wind and temperature profiles in the lowest 2000 m of the atmosphere at Halley (75°35′S, 26°50′W) have been analysed. Surface winds blow most frequently from the sector 090° ± 45° but the 2000 m wind direction is much more evenly distributed and appears to be determined by synoptic-scale pressure gradients. A simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.