On the Nongeostrophic Appearance of Some Mean Surface Velocity Observations in the Gulf of Mexico

A previous study by the author concluded that either there were errors in the satellite results or that some long-term means were not in geostrophic balance. Ship-drift results are in good agreement with surface drifters, but these two do not agree with satellite sea surface heights (SSH). The agreement between the first two suggested the possibility that there could be errors in the SSH or that the mean surface flow is not in geostrophic balance. The present results, using the addition of a fourth long-term mean from hydrographic data, which agrees with the SSH, resolves the issue. The lack of agreement between different long-term means is from inadequate coverage in space and time in data from ship drifts and drifters.