Possible ionospheric preconditioning by shear flow leading to equatorial spread F

D. L. Hysell (1) , E. Kudeki (2) , J. L. Chau (3)

1 EAS - Department of Earth and Atmospheric Sciences [Ithaca)
2 University of Illinois - Department of Electrical and Computer Engineering [Urbana]
3 Radio Observatorio de Jicamarca

Vertical shear in the zonal plasma drift speed is apparent in incoherent and coherent scatter radar observations of the bottomside F region ionosphere made at Jicamarca from about 1600?2200 LT. The relative importance of the factors controlling the shear, which include competition between the E and F region dynamos as well as vertical currents driven in the E and F regions at the dip equator, is presently unknown. Bottom-type scattering layers arise in strata where the neutral and plasma drifts differ widely, and periodic structuring of irregularities within the layers is telltale of intermediate-scale waves in the bottomside. These precursor waves appear to be able to seed ionospheric interchange instabilities and initiate full-blown equatorial spread F. The seed or precursor waves may be generated by a collisional shear instability. However, assessing the viability of shear instability requires measurements of the same parameters needed to understand shear flow quantitatively - thermospheric neutral wind and off-equatorial conductivity profiles.

Keywords. Ionosphere (Equatorial ionosphere; ionospheric irregularities) ? Space plasma physics (Waves and instabilities)

Domaines: Océan, Atmosphère; Sciences de la Terre

D. L. Hysell, E. Kudeki, J. L. Chau. Possible ionospheric preconditioning by shear flow leading to equatorial spread F. Annales Geophysicae, 2005, 23 (7), pp.2647-2655. ⟨hal-00317904⟩