Five barotropic modes of oscillation are computed for a hemispherical basin centered on the equator of a rotating earth. The method of Longuet-Higgins and Pond (1970), which takes full account of horizontal divergence and the sphericity of the earth, is used. Two of the modes are planetary modes and three are gravity modes. Periods of oscillation for the five modes range from one day to over four days....
Christensen, Niels. 1973. "On free modes of oscillation of a hemispherical basin centered on the equator." Journal of Marine Research 31, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1265