Bispectra of spike-array type time series and their application to the analysis of oceanic microstructures

Abstract

Bispectral analysis is applied to records of the vertical profile of the vertical temperature gradient in the oceanic thermocline in the San Diego Trough. The bispectra exhibit three notable features; (1) bispectral peaks at the points (0.2 m⁻¹, 0.2 m⁻¹) and (0.2 m⁻¹, 0.1 m⁻¹), (2) bispectral ridges along the lines (Ω ₁=Ω ₀,Ω ₂=Ω ₀ andΩ ₁+Ω ₂=Ω ₀ corresponding to peak wavenumbersΩ ₀ in power spectra, and (3) array of bispectral peaks of interval of 0.2 m⁻¹ The results are compared with the bispectra of several modeled time series of spike-array type. The periodicity of 5 m found in the records seems to have two meanings: spacing of predominant spikes and wavelength of predominant sinusoidal wave. If this indicates the existence of internal waves having a vertical wavelength the same as the scale of homogeneous layers, it would suggest the possible importance of internal waves in the formation and maintenance mechanisms of oceanic microstructure.