Presenter: David Halpern (Scripps Institution of Oceanography)

Description:
We compared 1-h averaged ECCOv4r4 estimates and in-situ acoustic Doppler current profiler (ADCP) measurements of the Equatorial Undercurrent (EUC) on the Pacific equator at 165°E, 170°W, 140°W and 110°W in 10- to 14-year intervals in 1996-2010. At each site, ECCOv4r4 and ADCP EUC thicknesses were similar; ECCOv4r4 and ADCP depths of the EUC core speed were similar; and the ECCOv4r4 EUC core speed was about 50% as large as ADCP observations. The ECCOv4r4 standard deviation of the core speed was about 70% as large as those determined with ADCP measurements at 170°W, 140°W and 110°W, but was larger at 165°E. At each site, the mean ECCOv4r4 transport per unit width (TPUW) was approximately 30-60% less than that computed with ADCP measurements, with minimum and maximum values of both datasets at 165°E and 140°W, respectively. As the EUC moved eastward from 165°E to 140°W, its strength increased with inflows from below and from the south and north. However, ECCOv4r4  estimates of TPUWs gained a much smaller mass compared to ADCP observations. From 140°W to 110°W, both ECCOv4r4 and ADCP showed the same mass loss, although at 110°W the ECCOv4r4 EUC strength was about 30% smaller than ADCP data. Upper-layer depth-averaged Richardson Numbers (Ri) were evaluated between the depth of the EUC core speed and the upper depth where the eastward current reached 0.2 m s-1, with the Brunt-Väisälä frequency determined from 1995-2004 mean monthly density profiles. Compared to ECCOv4r4 Ri, ADCP Ri were more likely to be less than 0.25 by factors of 2.3-4.1 at 170°W, 140°W and 110°W, indicating a potential re-evaluation of the ECCOv4r4 vertical mixing parameterization. The impact on ECCOv4r4 by the quantity of in-situ salinity and temperature measurements will be described. The impact of the 45-km latitudinal dimension of the model grid will be assessed. Spectral analyses of ECCOv4r4 and ADCP meridional currents will be examined for evidence of 17- to 20-day oscillations.