Mid-depth Circulation of the World’s Oceans: A First Look at the Argo Array
Josh Willis(1) and Lee-Lueng Fu(1)
Jet Propulsion Laboratory,
Pasadena, CA 91109,
Satellite-based measurements of sea-surface height provide data that is highly complimentary to a wide variety of in situ data sets. One of the most robust such data sets is the Argo array of profiling floats. As of September, 2005, the Argo array has reached almost two-thirds of its target density and consists of more than 1900 floats, which now provide near-global coverage. In addition to producing a wealth of temperature and salinity profiles, Argo floats provide estimates of the mid-depth ocean circulation by drifting at a depth of 1000m over a period of 10 days. With roughly 3500 float-years of data now available, a preliminary estimate of the mid-depth circulation can now be produced for most of the oceans using Argo data. Estimates of the velocity field and dynamic height at 1000m depth will be presented. Altimeter-based estimates of sea-surface height anomaly also contain information about the geostrophic velocity field. In addition to the estimates of mid-depth circulation, the relationship between anomalous geostrophic velocity at the surface and 1000m float displacements was explored. Over much of the ocean, the altimeter data was found to be complimentary to the float displacement data and a technique was developed for combining these two datasets to create improved estimates of the time-averaged velocity field at 1000m. The altimeter data is first used to estimate anomalous geostrophic velocity at depth, which is then used to correct individual float displacements. Although improvements to individual float trajectories are not always discernable, the correction significantly reduces the variance of the displacement data and improves the signal to noise ratio by 50% in most regions, and more in regions of high eddy variability.