Equinoctial transitions in the ionosphere and thermosphere

A. V. Mikhailov (1) , K. Schlegel (2)

1 IZMIRAN - Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation
2 MPI Aeronomie - Max-Planck-Institut für Aeronomie

Equinoctial summer/winter transitions in the parameters of the F2-region are analyzed using ground-based ionosonde and incoherent scatter observations. Average transition from one type of diurnal NmF2 variation to another takes 20?25 days, but cases of very fast (6?10 days) transitions are observed as well. Strong day-time NmF2 deviations of both signs from the monthly median, not related to geomagnetic activity, are revealed for the transition periods. Both longitudinal and latitudinal variations take place for the amplitude of such quiet time NmF2 deviations. The summer-type diurnal NmF2 variation during the transition period is characterized by decreased atomic oxygen concentration [O] and a small equatorward thermospheric wind compared to winter-type days with strong poleward wind and increased [O]. Molecular N₂ and O₂ concentrations remain practically unchanged in such day-to-day transitions. The main cause of the F2-layer variations during the transition periods is the change of atomic oxygen abundance in the thermosphere related to changes of global thermospheric circulation. A possible relationship with an equinoctial transition of atomic oxygen at the E-region heights is discussed.

Domaines: Océan, Atmosphère; Sciences de la Terre

A. V. Mikhailov, K. Schlegel. Equinoctial transitions in the ionosphere and thermosphere. Annales Geophysicae, 2001, 19 (7), pp.783-796. ⟨hal-00316875⟩