Wave coupling between the lower and upper atmosphere: case study of an ultra-fast Kelvin Wave

Since the first published issue of the Journal of Atmospheric and Terrestrial Physics, many papers have been devoted to the topic of wave coupling between atmospheric regions. The present work has two primary objectives. First, we review the effects of mean winds and dissipation on the Vertical propagation of high-phase-speed planetary-scale waves from troposphere and stratosphere sources into the mesosphere and thermosphere, drawing on a number of milestone research papers published over the past 35 years. The emphasis here is on departures from the 'textbook' or 'classical' theory of atmospheric waves. Second, we apply these principles to the vertical propagation of an 'ultra-fast' Kelvin wave with period of 3 days and zonal wavenumber equal to one, for which new numerical results are presented. In classical theory without dissipation, this wave is equatorially trapped and has small meridional velocities. It is shown here that in the dissipative thermosphere this wave has non-negligible meridional velocities with maxima at the poles. In addition, westward (eastward) mean zonal mesospheric winds near the equator Doppler-shift the wave to higher (lower) frequencies and increase (decrease) its vertical wavelength, thus reducing (increasing) its susceptibility to dissipation. Winds asymmetric about the equator are found to distort locally the latitudinal shapes of the Kelvin wave fields by coupling into modes which tend to remain confined to the level of excitation. For realistic forcing, dissipation and mean wind configurations, it is shown that the Kelvin wave is capable of achieving amplitudes of order 10-25 K in temperature and 10-40 m s(-1) in zonal wind in the 100-150 km height regime, and producing zonal mean eastward accelerations of order 10-15 m s(-1) day(-1). The Kelvin wave perturbations aught in addition to have significant effects on the dynamo generation of electric fields, the layering of metallic ions, and on variations in various airglow emissions originating between 90 and 105 km altitude. (C) 2000 Elsevier Science Ltd. All rights reserved.