Comparisons of sea surface height variability observed by pressure-recording inverted echo sounders and satellite altimetry in the Kuroshio Extension
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Satellite-measured along-track and gridded sea surface height (SSH) anomaly products from AVISO are compared with in situ SSH anomaly measurements from an array of 43 pressure-recording inverted echo sounders (PIESs) in the Kuroshio Extension. PIESs measure bottom pressure (P bot) and round-trip acoustic travel time from the sea floor to the sea surface (τ). The P bot and τ measurements are used to estimate, respectively, the mass-loading and steric height variations in SSH anomaly. All comparisons are made after accurate removal of tidal components from all data. Overall good correlations are found between along-track and PIES-derived SSH anomalies with mean correlation coefficient of 0.97. Comparisons between the two measurements reveal that the mass-loading component estimated from P bot is relatively small in this geographical region. It improves regression coefficients about 5 % and decreases mean root-mean-squared (rms) differences from 7.8 to 6.4 cm. The AVISO up-to-date gridded product, which merges all available satellite measurements of Jason-1, Envisat, Geosat Follow-On, and TOPEX/Poseidon interlaced, shows better correlations and smaller rms differences than the AVISO reference gridded product, which merges only Jason-1 and Envisat. Especially, the up-to-date gridded product reveals 6.8 cm rms improvement on average at sites away from Jason-1 ground tracks. Gridded products exhibit low correlation (0.75–0.9) with PIES-derived SSH in a subregion where the SSH fluctuations have relatively high energy at periods shorter than 20 days.
KeywordsSea surface height Pressure-recording inverted echo sounder (PIES) Satellite altimetry Kuroshio Extension Acoustic echo time Ocean bottom pressure
We are grateful to Andrew D. Greene for producing the initial version of GEM fields that were used for the PIES steric height calculations, and to Amy L. Cutting who assisted in early stages on a summer undergraduate research experience (REU), both under NSF support. This work was supported by NSF grants OCE-0221008 and OCE-0851246, and J.H.P. was also supported by KORDI grants PE98731 and PE98742.
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