amplitude spectrum

In the Fourier or spectral analysis of two time series, a measure of the correlation between the two series as a function of frequency or wavelength, but ignoring any phase differences between the two time series.

It is defined as

where n is wavenumber (number of waves per total period of the time series), Co(n) is the cospectrum, and Q(n) is the quadrature spectrum.
Stull, R. B. 1988. An Introduction to Boundary Layer Meteorology. 666 pp.

1. The study of the physics, chemistry, and dynamics of the earth's atmosphere, including the related effects at the air–earth boundary over both land and the oceans. Fundamental topics include the composition, structure, and motion of the atmosphere. The goals ascribed to meteorology are the complete understanding and accurate prediction of atmospheric phenomena.