Equatorial Kelvin-like waves on slowly rotating and/or small-sized spheres: Application to Venus and Titan

Abstract

Equatorial Kelvin waves, which have been observed in planetary fluids, produce superrotation and climatological variability. Although the meridional flow component is zero on Earth's beta-plane in the absence of background basic flow, it cannot be neglected on spheres in some planetary fluids when the Lamb parameter is small. For a vertically propagating Kelvin-like wave in the absence of background wind shear, meridional flows produce equatorward heat transport, i.e., a downward Eliassen-Palm flux. The vertical momentum transport caused by the equatorward heat flux has a theoretical upper limit, and the normalized flux is analytically expressed as a simple function that is independent of the Lamb parameter. On a slowly rotating and/or small-sized planet, we need to consider the meridional flow component of the equatorial Kelvin-like wave and its related heat flux on the sphere, and further consider their modification owing to background flow shear through coupling with high-latitude Rossby waves.