Horizontal wave number distribution of potential energy in the ocean

Abstract

Horizontal spectra of temperature fluctuations on wavelengths from the mesoscale to the fine scale and spectra of conductivity fluctuations on the microscale are reported. These spectra are combined with intermediate‐scale isopycnal displacement data of Katz (1973), and a composite potential energy spectrum is constructed which spans scales from 2 cm to 2000 km, a range of eight decades in wave number. The overlap in energy level between scales is remarkably consistent, even though the data were acquired in different oceans and at depths from 60 to 600 m. This composite spectrum can be fit roughly by a −2 power law across these scales, and excesses above this level occur near 500 km, near 1 km, and on scales less than about 15 m. The excesses at the longest and shortest scales are apparent when energetic features, specifically mesoscale eddies and fine‐structure and microstructure patches, occur in the data. Spectral levels vary by an order of magnitude on the mesoscale and by 3 orders of magnitude on the fine scale and microscale. There appears to be a minimum in the relative variability in spectral level in the band from 1 to 50 km.

Oceanic Isopycnal Slope Spectra. Part I: Internal Waves

“…The saturated subrange in the vertical also yields a weak amplitude dependence of the horizontal spectra on internal wave energy level. The calculated horizontal spectra roughly agree with the data (McKean and Ewart 1974;Katz 1975;Katz and Briscoe 1979;Dugan et al 1986). …”

“…Like the vertical measurements, these studies found relatively universal spectra in the open ocean and fit these spectra to a single subrange. The best fit was x ϳ k Ϫ0.5 x with a whitening at low wavenumbers (McKean and Ewart 1974;Katz 1975;Katz and Briscoe 1979;Dugan et al 1986). This work led to an older version of the Garrett-Munk fit (hereinafter referred to as GM75; Garrett and Munk 1975).…”

Of Ocean Waves and Sea Ice

“…Data for the frequency band 0.1-100 Hz were measured directly with vertically oriented geo phones; those between 0.02 and I Hz were temporally integrated from accelerometer records; others were calculated theoretically. The hypothesis is that any observed spectrum is a combination of these component parts (Dugan et al 1986); each specific curve has been selected to emphasize a physical mechanism which is now discussed in more detail.…”

Oceanic Isopycnal Slope Spectra. Part II: Turbulence

“…There is a substantial literature describing horizontal temperature spectra in the ocean, much of it overlapping the scales discussed here (McKean and Ewart 1974;Katz 1975;Katz and Briscoe 1979;Marmorino 1987;Dugan et al 1986). These spectra share many of the characteristics of the spectra sketched in Fig.…”