Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

Abstract

Abstract. 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.

Rocket and radar investigation of background electrodynamics and bottom-type scattering layers at the onset of equatorial spread <i>F</i>

“…An approximate expression for the linear growth rate of the instability can be written as (Hysell et al, 2005):…”

Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread <I>F</I>

“…Heelis et al, 1974), recent results have shown that other factors can be potentially important as well. These factors would include zonal electric fields on flux tubes with significant Hall conductivity, vertical winds, and vertical boundary currents forced from above or below the flux tube in question (Haerendel et al, 1992;Hysell et al, 2005a).…”

Mission Support for the Communication/Navigation Outage Forecast System (C/NOFS) Satellite

“…On occasions when topside spread F occurs, the bottom-type layers seem to be organized in clusters separated by tens or hundreds of km [31]. We know this from interferometric/imaging experiments at Jicamarca and also from coherent and incoherent scatter radar scans from the Altair radar on Kwajalein Atoll.…”