Sea Surface Height Variability in Drake Passage

• Published in: Journal of atmospheric and oceanic technology 2016-04, Vol.33 (4), p.669-683
• Main Authors: Donohue, Kathleen A, Kennelly, Maureen A, Cutting, Amy
• Format: Article
• Language: English
• Subjects: Altimeters; Altimetry; Antarctic front; Atmospherics; Boundaries; Compounding; Compounds; Continental slope; Correlation coefficient; Experiments; Fracture mechanics; Geopotential height; Marine; Ocean circulation; Sampling; Variance
• ISSN: 0739-0572; 1520-0426
• DOI: 10.1175/JTECH-D-15-0249.1

Intercomparisons between altimeter sea surface height (SSH) and open-ocean in situ observations have been limited owing to sparse available datasets. Here, SSH anomaly (SSHA) determined from current and pressure recording inverted echo sounders (CPIES) from the cDrake experiment were compared with an up-to-date AVISO-mapped product. Meandering Antarctic Circumpolar Current (ACC) fronts in the passage interior elevated SSHA variance; south of the Shackleton Fracture Zone and along the northern continental slope, the variance decreased by factors between 6 and 10. In situ analysis focused on the two constituents of SSHA, SSHA sub(ref) determined from bottom pressure and SSHA sub(bcb) calculated from geopotential height referenced to the bottom. The peak variance of both SSHA sub(bcb) and SSHA sub(ref) occurred in the energetic region between the Subantarctic Front and the Polar Front. The contribution of SSHA sub(bcb) to total SSHA variance was greater than 40% at all sites and averaged over all sites it was 73%. For most sites, high-frequency (>1/20 cpd) SSHA sub(bcb) signals dominated total high-frequency variance. Aliasing of high-frequency signals resulting from 10-day altimeter sampling was assessed. The fraction of aliased energy at frequencies longer than 1/50 cpd for sites at and north of the Shackleton Fracture Zone approached 0.25 and approached 0.50 for southern sites. CPIES and mapped altimeter SSHA agreed well. The mean correlation coefficient was 0.82 and the mean RMS difference was 0.075 m. Correlations between CPIES and AVISO were notably poorer at the northern and southern boundaries. RMS differences increased as a function of CPIES high-frequency SSHA variance because the mapped altimetry product does not resolve these frequencies.