Tuesday 23 August 2005

PB3
1400-1520 hours

186
Internal gravity waves in McMurdo Sound, Antarctica
Albrecht, Nicole¹, Williams, Mike², Vennell, Ross³, Stevens, Craig², Langhorne, Pat¹
1 University Of Otago, Department Of Physics, Dunedin, New Zealand
2 National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
3 University Of Otago, Department Of Marine Science, Dunedin, New Zealand
Author email: nalbrecht@physics.otago.ac.nz
Mooring and CTD data from winter (April-September 2003) and summer (November 2004) in McMurdo Sound, Antarctica, have been analysed for internal wave activity. Spectra of moorings show that McMurdo Sound has internal tides with the main frequencies at the diurnal and semidiurnal frequency bands. The energy in the third- and fourth-diurnal frequency bands was much weaker, but still identifiable. All of these frequencies are below the Coriolis frequency, f, at this latitude. Thus the associated internal waves are not freely propagating, and are likely to be edge waves. For frequencies between f and the buoyancy frequency, N, the internal wave energy in McMurdo Sound has more energy than the Garrett Munk-spectrum. This differs from prior polar observations, which usually have less energy due to the lack of input from wind and surface waves. Our results are most likely explained by our choice of study site, as here the necessary conditions of the GM spectrum are not met, as we have shallow water, a sharp change in topography and are close to the coast. The analysis shows that the internal wave activity varies with season. This variation is consistent with that observed in the density, a sharp decrease with season. The sources and exact structure for the internal waves are difficult to determine in a complicated setting like McMurdo Sound, but the analysis suggests that it a mixture of medium and large scale wave processes caused by interaction between topographic features and baroclinic tides.

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