Wave dynamics in the thermosphere: I: Tidal motion

The atmospheric tides, their transmission and excitation in the thermosphere, are discussed in reviewing various investigations in this field. We are still fairly ignorant on the subjects and facing various unsolved problems although there is an established link between the theory and the observation in the dynamo region, the lower boundary of the thermosphere. As to the middle and upper thermosphere the observed data are scanty and only those obtained by satellite drag are available; the theoretical approach is very complicated because of viscosity, thermal conduction, hydromagnetic forces and non-linearity, all of which are effective above certain heights. Moreover, the thermosphere couples mainly with the lower atmosphere, this coupling having been considered only in a very simplified way. Another coupling is between thermal excitation and the resultant motion, the coupling of which has never been considered; thermal excitation has been discussed on a given input. International cooperation in the observations is of vital importance for future studies. New developments of observation techniques are desirable.