Newfoundland Basin sea-level variability from TOPEX/POSEIDON altimetry and inverted echo sounder - bottom pressure measurements

A collaborative deep-sea study of the North Atlantic Current in the Newfoundland Basin by the University of Rhode Island and the Bedford Institute of Oceanography took place during 1993-1995. The study included an array of three collocated bottom pressure sensors and inverted echo sounders (PIES) which spanned a 320-km cross section of the North Atlantic Current. The bottom-moored inverted echo sounders measure full-depth acoustic travel time and provide an estimate of geopotential height. The sum of the geopotential height and the depth equivalent of bottom pressure gives an estimate of sea-level height. Time variations in PIES sea level are compared with measurements by the TOPEX/POSEIDON (T/P) altimetric satellite during the 22-month time period from August 1993 to July 1995. The three sites show remarkably different baroclinic structures, energy levels, and space-time characteristics. Time scales are such that 86-95% of the subinertial period sea-level variability at the three sites is not aliased by the approximately 10-day T/P repeat period sampling. The T/P spatial sampling, however, is insufficient for mapping the mesoscale variability. The PIES and T/P sea-level time series were highly correlated for two cases where the nearest T/P measurement points were within 15-30 km of the PIES site. A third site with the closest T/P measurement nearly 100 kin removed was essentially uncorrelated with any T/P measurements. Parametric space-time correlation models based on the T/P and PIES sea-level measurements are developed for each site to quantify the limitations of the T/P sampling. These examples illustrate the requirement for multi-satellite altimetric missions to provide more complete spatial coverage in this and similar western boundary current regions.