ZONALLY SYMMETRICAL DIURNAL TIDES SIMULATED WITH A GENERAL-CIRCULATION MODEL

A large zonally symmetric diurnal variation is found in temperature and wind fields in a model general circulation of the middle atmosphere. This variation has a vertical wavelength of about 25 km and shows similar structures to those of the basic mode of zonally symmetric diurnal tides. The zonal component of diabatic heating projected to the horizontal structure function of this mode shows a prominent diurnal change with large amplitudes near the surface. The simulated zonally symmetric diurnal variation therefore is the basic mode of the upward propagating tides thermally excited in the lower troposphere, the amplitude of which mode becomes appreciably large in the middle atmosphere due to the density effect.