Kelvin wave propagation in the upper atmospheres of Mars and Earth

Abstract

The propagation characteristics of a diurnal Kelvin wave (DKW) in the atmosphere of Mars and a 3-day Kelvin wave in the terrestrial atmosphere are compared and interpreted for Northern Hemisphere summer conditions (Ls = 90 and July, respectively). Significant horizontal wind and temperature perturbations are shown to accompany these oscillations in the thermospheres of both planets: ∼10–40 ms −1 and 10–25 K on Earth and 20–70 ms −1 and 10–30 K on Mars. Molecular dissipation on both planets serves to latitudinally broaden the thermospheric response, and to induce meridional wind maxima at the poles. On Earth, mean zonal winds asymmetric about the equator are found to locally (in altitude) distort the latitudinal shapes of the Kelvin wave fields by coupling into modes which tend to remain confined to the level of excitation, and which are equatorially trapped. On Mars the first asymmetric eastward propagating mode with vertical wavelength of about 60 km is very efficiently induced by the asymmetric zonal mean winds in the middle atmosphere; this wave component propagates well into the thermosphere and accounts for much global asymmetry seen in the wave fields.