Measurement of ocean waves and ice coupled waves near a fast ice boundary, McMurdo Sound

Ocean waves interact with Antarctic ice. Pack ice acts as a barrier to wave penetration, and attenuates the propagating waves. The presence of fast ice changes the nature of the wave interaction so that the wave characteristics are now determined by the properties of the ice. The interaction of ocean wave with the fast ice boundary and its contribution to ice breakup was determined experimentally over three seasons of study. The transfer of ocean wave energy into sea ice was measured using a portable microwave radar on Tent Island, McMurdo Sound. The radar derives ocean wave height spectra by measuring the ocean surface velocity as it varies under the action of the waves. The aim of the study was to position the radar close to a fast ice boundary, recording data during periods of ocean wave activity in order to determine the incident wave fields and the nature of the wave reflections. The interactions of ocean waves with both fixed and pack ice and the nature of the radar backscatter from these media was also investigated. In the first season, the radar was operated each day from the 20th to the 27th of January, 1991. During this time, the sea surface around Tent Island changed from a combination of fast and pack ice to continuous open sea to the north and west. In the second season, the radar was operated each day from the 14th to the 27th of January, 1992. The sea ice near Tent Island broke away rapidly in strong southerly conditions but several useful data sets were obtained. All opportunities were exploited to record worthwhile data in the conditions. Four situations were recorded; 1) Radar reflections during calm conditions were recorded from distant pack ice adjacent to the boundary of the fast ice and a water ice mixture close to Tent Island. 2) Strong southerly conditions caused the sea ice to break up and drift away. Radar data was recorded from the substantial drifting ice floes as they passed the radar site. 3) With nothing but clear sea in the radar field of view, a 24 hour data set was obtained of the sea surface drifts near Tent Island to determine the nature of the drifts. 4) A series of measurements were completed to obtain data on the basic nature of radar backscatter from a roughened sea surface when the fetch is small. These data include a range of grazing angles and different polarizations of the radar antenna and will be compared with contemporary theories of microwave backscatter from the sea surface. In the third season, the aims were to determine the spectral distribution of the available ocean wave energy at the fast ice boundary and the proportions of it that are either reflected or transmitted into the ice, and to compare the radar wave data with strain gauges placed in the fast ice to determine the characteristics of the ice coupled waves and their response to the ocean wave forcing. The radar was operated at Backdoor Bay, Cape Royds and at the sea ice edge near Cape Royds from the 22nd of November until the 8th of December in 1992. The radar wave data was compared with strain gauges placed in the fast ice to determine the characteristics of the ice coupled waves and their response to the ocean wave forcing. The measurements conducted include; a) radar measurements of the sea surface adjacent to the ice edge, b) strain gauge measurements in the ice, c) the configuration of the ice edge and in situ ice core sampling and d) underwater acoustic measurements. The microwave radar was mounted on a 15 m tower and installed close to the ice edge. The strain gauges were installed in the ice, in arrays up to 1 km back from the ice edge. Simultaneous measurements were made under two conditions, with an onshore and offshore wind.