Wavenumber Spectrum in the Gulf Stream from Shipboard ADCP Observations and Comparison with Altimetry Measurements

The wavenumber spectra for velocity and temperature in the Gulf Stream region are calculated from a decade (1994–2004) of shipboard acoustic Doppler current profiler (ADCP) measurements taken as part of the Oleander Project. The velocity and temperature spectra have comparable magnitude, in terms of the kinetic and potential energy, and both indicate a k−3 slope in the mesoscales. In contrast, the corresponding velocity spectrum determined from satellite altimetry sea surface heights yields a significantly higher energy level and a k−2 slope. The discrepancy between altimeter-derived and directly measured velocity spectra suggests that altimetric velocity probably is contaminated by noise in sea surface height measurement. Also, the k−3 slope, which appears to be in agreement with two-dimensional quasigeostrophic turbulence theory, does not support the contemporary surface quasigeostrophic theory. These results highlight large gaps in the current understanding of the nature of surface geostrophic turbulence.