The Effects of Altimeter Instrument Noise on the Estimation of the Wavenumber Spectrum of Sea Surface Height

Yongsheng Xu Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China

Search for other papers by Yongsheng Xu in
Current site
Google Scholar
PubMed
Close
and
Lee-Lueng Fu Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

Search for other papers by Lee-Lueng Fu in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The wavenumber spectrum of sea surface height (SSH) observed by satellite altimetry was analyzed by Xu and Fu. The spectral shape in the wavelength range of 70–250 km was approximated by a power law, representing a regime governed by geostrophic turbulence theories. The effects of altimeter instrument noise were assumed insignificant at wavelengths longer than 70 km. The authors reexamined the assumption in the study. Using nearly simultaneous observations made by Jason-1 and Jason-2 during their cross-calibration phase, this study found that the white noise level of altimetry measurement was best estimated from the spectral values at wavelengths from 25 to 35 km. After removing a white noise level based on such estimate from the SSH spectrum, the spectral slope values changed significantly over most of the oceans. A key finding is that the spectral slopes are generally steeper than k−2 (k is wavenumber) poleward of the 20° latitudes, where flatter spectral slopes in some regions have previously caused problems for dynamic interpretations. The new results indicate that the spectral slopes in the core regions of the major ocean current systems have values between the original geostrophic turbulence theory and the surface quasigeostrophic theory. The near k−4 spectrum suggests that the sea surface height variability at these wavelengths in the high eddy energy regions might be governed by frontogenesis.

Corresponding author address: Yongsheng Xu, Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China. E-mail: yongsheng.xu@qdio.ac.cn

Abstract

The wavenumber spectrum of sea surface height (SSH) observed by satellite altimetry was analyzed by Xu and Fu. The spectral shape in the wavelength range of 70–250 km was approximated by a power law, representing a regime governed by geostrophic turbulence theories. The effects of altimeter instrument noise were assumed insignificant at wavelengths longer than 70 km. The authors reexamined the assumption in the study. Using nearly simultaneous observations made by Jason-1 and Jason-2 during their cross-calibration phase, this study found that the white noise level of altimetry measurement was best estimated from the spectral values at wavelengths from 25 to 35 km. After removing a white noise level based on such estimate from the SSH spectrum, the spectral slope values changed significantly over most of the oceans. A key finding is that the spectral slopes are generally steeper than k−2 (k is wavenumber) poleward of the 20° latitudes, where flatter spectral slopes in some regions have previously caused problems for dynamic interpretations. The new results indicate that the spectral slopes in the core regions of the major ocean current systems have values between the original geostrophic turbulence theory and the surface quasigeostrophic theory. The near k−4 spectrum suggests that the sea surface height variability at these wavelengths in the high eddy energy regions might be governed by frontogenesis.

Corresponding author address: Yongsheng Xu, Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China. E-mail: yongsheng.xu@qdio.ac.cn
Save
  • Bonnefond, P., P. Exertier, O. Laurain, and G. Jan, 2010: Absolute calibration of Jason-1 and Jason-2 altimeters in Corsica during the formation flight phase. Mar. Geod., 33 (S1), 8090.

    • Search Google Scholar
    • Export Citation
  • Boyd, J. P., 1992: The energy spectrum of fronts: Time evolution of shocks in Burger’s equation. J. Atmos. Sci., 49, 128139.

  • Capet, X., P. Klein, B. Hua, G. Lapeyre, and J. C. McWilliams, 2008: Surface kinetic energy transfer in surface quasi-geostrophic flows. J. Fluid Mech., 604, 165174.

    • Search Google Scholar
    • Export Citation
  • Charney, J. G., 1971: Geostrophic turbulence. J. Atmos. Sci., 28, 10871094.

  • Held, I. M., R. T. Pierrehumbert, S. T. Garner, and K. L. Swanson, 1995: Surface quasi-geostrophic dynamics. J. Fluid Mech., 282, 120.

    • Search Google Scholar
    • Export Citation
  • Le Traon, P.-Y., P. Klein, and B. L. Hua, 2008: Do altimeter wavenumber spectra agree with the interior or surface quasigeostrophic theory? J. Phys. Oceanogr., 38, 11371142.

    • Search Google Scholar
    • Export Citation
  • Xu, Y., and L.-L. Fu, 2011: Global variability of the wavenumber spectrum of oceanic mesoscale turbulence. J. Phys. Oceanogr., 41, 802809.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 969 241 47
PDF Downloads 730 186 24