The stabilizing effect of collision‐induced velocity shear on the ionospheric feedback instability in Earth's magnetosphere. Issue 13 (15th July 2017)

• Record Type: Journal Article
• Authors: Sydorenko, D.; Rankin, R.
• Is Part Of: Geophysical research letters. Volume 44:Issue 13(2017)
• Page Start: 6534
• Page End: 6542
• Publication Date: 2017-07-15
• Subjects: ionospheric feedback instability -- ionospheric E layer -- ion flow shear -- Pedersen mobility -- height‐integrated conductivity -- ionospheric Alfvén resonator; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL073415
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The feedback instability in the ionospheric Alfvén resonator in Earth's magnetosphere is examined using a two‐dimensional multifluid numerical model of coupled ionosphere and magnetosphere. Two simulation configurations are used to demonstrate that the instability occurs under an assumption that is unrealistic for Earth's ionosphere. In the first configuration, a flat sheet height‐integrated conducting boundary replaces the ionospheric E layer. In the second configuration, plasma dynamics in a simplified E layer is resolved ignoring ion production, loss, and diffusion. For the same parameters (plasma and neutral density profiles and convection electric field), the instability develops only with the flat sheet boundary. When the E layer is resolved, the variation of ion‐neutral collision frequencies with altitude produces vertical shear in the horizontal ion flow velocity. The shear prevents density perturbations from remaining field aligned, causing them to decay rather than grow. It is suggested that the instability cannot occur in Earth's ionosphere because ion‐neutral collision frequencies always have a significant variation with altitude through the E layer. Key Points: The ionospheric feedback instability is stabilized due to the strong vertical shear of horizontal ion flow in the E layer The shear distorts initially field‐aligned shape of an ionospheric density perturbation causing the perturbation to decay rather than grow Rapid decay of ion‐neutral collision frequency with altitude in the Earth's is not captured by available theories of feedback instability