On the Observed Characteristics of Quasi–Geostrophic Turbulence

Abstract

Observed perturbation kinetic and available energy are presented for a region about 3000 km on a side to study the horizontal homogeneity and general characteristics of geostrophic motions. Frequency spectral analysis is used to determine the dependence of these characteristics on time scales. For all time scales considered the perturbation energies display horizontal inhomogeneities, but these are less pronounced for shorter time scales. For time scales smaller than 4 days the spectra of horizontal kinetic and available potential energies decrease with increasing frequency, and approximately fit power laws with exponents between ?2 to ?3.5, depending on location. The frequency spectra for geostrophic vertical velocities are markedly different for different climatic locations. The frequency spectra are related to one-dimensional wavenumber spectra by introducing suitable transformation of variables. The results obtained for the higher end of these spectra are interpreted in terms of those predicted by Charney for quasi-geostrophic turbulence.