Wave dynamics in the thermosphere: I: Tidal motion

Abstract

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.

Wave motions in the atmosphere and related ionospheric phenomena

“…Haurwitz (1965) found that the observed diurnal barometric variation with latitude cannot be expressed by a combination of positive modes. These gave evidence for the existence of the negative mode in the atmosphere (Kato, 1971). Lindzen (1967a) discussed the thermal excitation of the diurnal and semi-diurnal tides by ozone and water vapour absorbing solar radiation.…”

“…Further, Tarpley (1970) found a current system induced by a given horizontal velocity with diurnal first negative mode ( Figure 13) to be very similar to that deduced from the geomagnetic Sq variations such as Chapman and Bartels (1940). Maeda, K. and Kato (1966), and Kato (1971) reviewed these problems in detail.…”

“…Therefore, this problem should be treated as one of the electrodynamics of planetary waves in the ionosphere. It is interesting to note in this connection (Kato, 1971) that there is a displacement of the Sq current vortex at a given local time from day to day (Hasegawa, 1936). The displacement is mainly in the north-south direction, sometimes with a small east-west component, and its principal period is about 10 days (Yanagihara, private communication, 1970).…”

“…The thermospheric expansion of the atmosphere by day induces the diurnal oscillation. These winds have been discussed by many authors and many review papers have been published (recently, Kato, 1971 andRishbeth, 1972a, b). The thermospheric wind system at F-layer heights could be regarded as a 'diurnal tide'.…”

“…Though the meteor wind radar method, and observations of chemical trails made by rockets, have detected ionospheric movements oscillating with diurnal and semidiurnal periods, no attempt has so far been made to prove the existence of tidal waves by simultaneous measurement of their wavelength along a circle of latitude (Kato, 1971). Further observations along a longitudinal circle are also necessary to find the longitudinal configuration.…”