Date of Award
Master of Science in Oceanography
As part of the International Polar Year, cDrake, an array of current and pressure recording inverted echo sounders (CPIES), was deployed in Drake Passage in November 2007. The array will be in place for four years and the data collected annually by acoustic telemetry. The CPIES array consists of a transport line, 22 CPIES that span Drake Passage and a local dynamics array, a grid of 21 CPIES centered on the surface eddy kinetic energy maximum in the passage. Acoustic round-trip travel time and bottom pressure anomaly are used to compute sea surface height anomaly (SSHA) at each site. Round-trip travel time measurements are converted to geopotential using historical hydrography. Geopotential is divided by gravity to determine the steric component of SSHA. The mass-loading component of SSHA is computed by dividing the bottom pressure anomaly by the product of density and local gravity. The mass-loading and steric SSHA components are uncorrelated, except in the eastern local dynamics array, at three sites where strong deep cyclone formation associated with the meandering Polar Front lead to correlation coefficients greater than 0.4. Relative contributions of steric and massloading components vary along the transport line. North of 57 degrees S, steric SSHA variance exceeds 60% of the total SSHA variance. South of 59 degrees S, the mass-loading SSHA variance exceeds 40% of the total SSHA variance and in places reaches 65% of the total variance.
The CPIES-derived SSHA is compared with SSHA from an along-track and a merged and mapped satellite SSHA product. Correlations with both products varied widely depending on the variability in the records, but most were above 0.9 and statistically significant. Notable exceptions occur along the southern end of the transport line, where correlations dip to 0.2-0.7. The Nyquist frequency of the Topex/Poseidon, Jason-1 and Jason-2 satellite repeat is 1/20 cycles-per-day. Signals with frequencies higher than this will get aliased by the altimeter sampling. In cDrake, the aliased variance exceeds 20% of the total signal variance in the middle of the dynamics array and on the southern end of the transport line. There is potential of aliasing of both the steric and massloading SSHA in Drake Passage. Analysis of the SSHA records with frequencies higher than 1/20 cpd from recovered cDrake instruments shows no correlation with the highfrequency barotropic model output used to correct altimetry measurements for high frequency signals. The model underestimates the signals throughout the cDrake array. Aliasing of these signals will continue unless a better correction for the mass-loading variance is found and a steric high-frequency correction is developed.
Cutting, Amy Lynn, "CONSTITUENTS OF SEA SURFACE HEIGHT VARIABILITY IN DRAKE PASSAGE" (2010). Open Access Master's Theses. Paper 1188.