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.