Vertical and latitudinal structure of the migrating diurnal tide in the Martian atmosphere: Numerical investigations

We investigate the vertical and latitudinal structure of the migrating diurnal tide in a low dust condition ( dust optical depth of 0.3 at 0.67 mu m) in the Martian atmosphere by using a general circulation model ( GCM) and a linear response model ( LRM). The migrating diurnal tide simulated in our Mars GCM well represents general characteristics of the migrating diurnal tide which have been reported in previous observational and GCM studies. The GCM simulation shows that the vertical wavelength of the migrating diurnal tide in the low latitude region at equinox is similar to 45 km which is larger than that of the major propagating mode predicted from the classical tidal theory ( similar to 25 - 35 km). The Hough function decomposition and the numerical experiments using the LRM reveal that the large vertical wavelength of the migrating diurnal tide is caused by the effects of the zonal mean vorticity (zeta) over bar. It is suggested that the vertical wavelength of the migrating diurnal tide increases through the changes of the effects of the planetary rotation in the presence of non-zero zonal mean vorticity (zeta) over bar . Such a strong dependence of the vertical wavelength of the migrating diurnal tide on (zeta) over bar is not observed in the Earth's atmosphere. The Martian radius, about the half of the Earth's radius, would be one of the important factors to cause more effective (zeta) over bar in the Martian atmosphere than that in the Earth's atmosphere.