Boundary value problems for the Laplace tidal wave equation

Abstract

This paper discusses the eigenvalue problem associated with the Laplace tidal wave equation (LTWE) given, for μ ϵ (—1,1), by 1 − μ 2 μ 2 − τ 2 y ′ ( μ ) ′ + 1 μ 2 − τ 2 s τ μ 2 + τ 2 μ 2 − τ 2 + s 2 1 + μ 2 y ( μ ) = λ y ( μ ) , ( LTWE ) where s and τ are parameters, with s an integer and 0 < τ < 1, and λ determines the eigenvalues. This ordinary differential equation is derived from a linear system of partial differential equations, which system serves as a mathematical model for the wave motion of a thin layer of fluid on a massive, rotating gravitational sphere. The problems raised by this differential equation are significant, for both the analytic and numerical studies of Sturm-Liouville equations, in respect of the interior singularities, at the points ± τ , and of the changes in sign of the leading coefficient (1 - μ 2 )/( μ 2 - τ 2 ) over the interval (-1, 1). Direct sum space methods, quasi-derivatives and transformation theory are used to determine three physically significant, well-posed boundary value problems from the Sturm-Liouville eigenvalue problem (LTWE), which has singular end-points ± 1 and, additionally, interior singularities at ± τ . Self-adjoint differential operators in appropriate Hilbert function spaces are constructed to represent each of the three well-posed boundary value problems derived from LTWE and it is shown that these three operators are unitarily equivalent. The qualitative nature of the common spectrum is discussed and finite energy properties of functions in the domains of the associated differential operators are studied. This work continues the studies of LTWE made by earlier workers, in particular Hough, Lamb, Longuet-Higgins and Lindzen.