North-south asymmetries in the thermosphere during the Last Maximum of the solar cycle

F. Barlier (1) , Pierre Bauer (2) , C. Jaeck (1) , Gérard Thuillier (3) , G. Kockarts (4)

1 GRGS - Groupe de Recherche de Géodésie Spatiale [Grasse]
2 CNET - Centre national d'études des télécommunications
3 SA - Service d'aéronomie
4 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique

A large volume of data (temperatures, densities, concentrations, winds, etc.) has been accumulated showing that in addition to seasonal changes in the thermosphere, annual variations are present and have a component that is a function of latitude. It appears that the helium concentrations have much larger variations in the southern hemisphere than in the northern hemisphere; the same holds true for the exospheric temperatures deduced from Ogo 6 data. Similarly, satellite drag data in the 250- to 400-km range indicate that the bulge of density tends to stay over the southern hemisphere, whereas winds deduced from Ogo 4 and 6 data show a tendency to blow northward across the equator. If part of the explanation of these asymmetries can be found in a latitude independent component induced by the changing sun-earth distance between solstices (Volland et al., 1972; Ching and Chiu, 1972, 1973), the fact that an asymmetry is still present at the equinoxes suggests that this is not the sole cause: more energy seems to be available for the thermosphere in the southern hemisphere during the equinoxes; this may be the result of an asymmetry in the geomagnetic field or an asymmetrical dissipation of tidal waves induced by an asymmetrical worldwide ozone distribution.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

F. Barlier, Pierre Bauer, C. Jaeck, Gérard Thuillier, G. Kockarts. North-south asymmetries in the thermosphere during the Last Maximum of the solar cycle. Journal of Geophysical Research Space Physics, 1974, 79, pp. 5273-5285. ⟨10.1029/JA079i034p05273⟩. ⟨hal-01627389⟩