Physical Review Letters
According to classical theories, the frequencies of internal-gravity waves in stratified rotating fluids must lie between the Brunt-Väisälä frequency (a measure of the vertical density stratification) and the Coriolis frequency (equal to twice the rotation rate about the vertical axis). It is shown here that, in the case of the Earth's rotation where the pole-to-pole axis of rotation is almost everywhere not parallel to the local vertical, the range of realizable frequencies is broader. New formulas are derived for the lower and upper bounds of the frequencies.
Cushman-Roisin, Benoit, "Lower and Upper Bounds on Internal-Wave Frequencies in Stratified Rotating Fluids" (1996). Open Dartmouth: Faculty Open Access Articles. 2020.