Normal Mode--Sphere -- from Eric Weisstein's World of Physics

Normal modes on a sphere consist of so-called S-modes and T-modes. S-modes are spheroidal vibrations which have radial as well as horizontal motions of fluid elements. They are labeled , where n is the number of internal nodal surfaces and l is the number of surface nodal lines. T-modes are torsional or toroidal vibrations which have purely tangential motions. They are labeled , where n is the number of internal nodal surfaces and is the number of surface nodal lines.

Normal Mode

References