Mesoscale Features in Surface Currents

Kathleen Dohan (Earth and Space Research, United States)

CoAuthors

Jonathan M. Lilly (NorthWest Research Associates, United States)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Science Results from Satellite Altimetry: Finer scale ocean processes (mesoscale and coastal)

Presentation type: Type Poster

Ocean Surface Current Analyses-Realtime currents (OSCAR, podaac.jpl.nasa.gov) are global ocean surface velocities calculated from sea surface height (SSH), ocean vector winds, and sea surface temperature fields using geostrophy, Ekman and thermal wind dynamics. OSCAR uses the AVISO gridded MADT sea surface height (SSH) fields (http://www.aviso.altimetry.fr/).

Compared with global surface drifters, velocity standard deviations are underestimated by 20-50% in OSCAR over much of the oceans. A considerable portion of this underestimation is likely attributable to the large degree of smoothing implicit in the creation of the AVISO gridded products.

Here we will apply the local polynomial fitting mapping methods used in the Aquarius Level 3 salinity gridding to altimetry fields. An important feature of local polynomial fitting over optimal interpolation methods (such as AVISO) is the order of fit: a first-order (linear) fit calculates gradients as part of the mapping. Geostrophic velocities will therefore be directly calculated from the data, which is expected to result in stronger, more accurate, albeit noisier, velocities.

The objective is to present preliminary results of a gridding process for the gradients of SSH which retains, rather than smooths out, the mesoscale and sub-mesoscale "noise". These new mesoscale surface currents will be examined in test locations with high concentrations of drifters for comparison, with particular attention to cases in which drifters cross the satellite tracks for a significant portion of time. Eventually this work will lead to a global mesoscale OSCAR.
 
Kathleen Dohan
Earth and Space Research
United States
kdohan@esr.org