Striation formation associated with barium clouds in an inhomogeneous ionosphere

Abstract

The present study investigates, via linear theory, how striations (treated as perturbations) created in a plasma cloud centered at 200 km will penetrate into the background inhomogeneous (real) ionosphere as a function of wavelength, integrated Pedersen conductivity ratio of the cloud to ionosphere (Z,ø/23,'), and ambient ionospheric conditions. The study is posed as an eigenvalue problem which while determining the potential variation (eigenmode) along magnetic field lines, self-consistently solves for the growth rate (eigenvalue) in the coupled cloud-inhomogeneous ionosphere system. Perturbed particle densities, fluxes parallel to the magnetic field B, and electrostatic potential are presented as a function of altitude. The results show the importance of the image transport parameter (kL•v,/Wc,)(1 + 'P,2/00C,2) -1 (where k is the wave number transverse to B, L• is the transverse dimension of the cloud, and v, ahd OOc, are the ionospheric ion-neutral collision frequency and ion cyclotron frequency, respectively) in determining the magnitude of imaging and aspect angle of striations with respect to B (i.e., striations take on a parallel component of wave number). Perturbations penetrate further down in the presence of the plasma cloud than was indicated in simple previous studies which neglected image transport and considered the perturbation mapping from one region of the ionosphere to another. Our results show that clouds with smaller conductivity ratios produce image striations further down into the background E region ionosphere with a more uniform coupling as a function of wavelength. It is further shown that there is a slight dependence of the E region coupling of the perturbations on the level of solar activity (solar maximum or minimum conditions) and also that this E region coupling shows a slight dependence on the extent of F region coupling above the cloud. Finally, with a fully self-consistent treatment of F region coupling, the growth rates show negligible short-wavelength damping due to ionospheric coupling for the 23•,b/23d = 4 case. [Farley, 1959[Farley, , 1960Spreiter and Briggs, 1961] that for transverse wavelengths of >• 1 km the magnetic field lines act as equipotenfials, i.e., shorter-wavelength electric field perturbations do not couple effectively from one region of the ionosphere to another. Most ideas about the potential variation along magnetic field lines, as a function of transverse wavelength, are based on these earlier works. Moreover, the multilevel two-dimensional theoretical and numerical simulation studies of barium clouds coupled to the background ionosphere [Lloyd and Haerendel, 1973; Goldman et al., 1974; Scannapieco et al., 1974] have assumed that the electric fields at the cloud level and the background ionosphere are the same. That is, the electric fields have only transverse spatial dependence in the two dimensions perpendicular to the magnetic field and no variation along the magnetic field lines. Estimates of striation behavior, based on linear theory and including coupl...

Effect of the Coupling of Different Ionospheric Regions on the Nighttime F Region Irregularities in Mid‐Latitude

“…Both the elements will lessen the growth rate in the F region. This is in accordance with earlier work [4][5][6]8,10] .…”

Low‐altitude image striations associated with bottomside equatorial spread F: Observations and theory

“…However, magnetic field lines can link unstable regions to other plasma populations that may affect the evolution of the instability process. An example is the role of a conducting E region in diffusive damping of F region structure and in the suppression of electrostatic instabilities [Volk and Haerendel, 1971;Goldman et al, 1976;Vickrey and Kelley, 1982].…”

A review of electrostatic wave measurements on auroral magnetic field lines.

“…The crossfield instability has been very successful in explaining the striations which develop in barium cloud releases (LINSON and WORKMAN, 1970;HAERENDEL and YOLK, 1971;PERKINS et al, 1973;ZABINSKY et al, 1973;GOLDMAN et al, 1976). In this instability enhanced density regions have slightly smaller electric fields than the ambient, and hence drift more slowly.…”