; it gives the
contribution to the third moment from the product of three Fourier components having frequencies which add to zero. It has
been used in many fields, notably geophysics, to study weak nonlinearities (see, e.g., [56, 80]).
; it gives the
contribution to the third moment from the product of three Fourier components having frequencies which add to zero. It has
been used in many fields, notably geophysics, to study weak nonlinearities (see, e.g., [56, 80]).