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[1] This paper presents novel features of subauroral ion drifts (SAID) observed from a unique conjunction of the Cluster, DMSP, and Polar satellites, including the discovery of SAID-related plasma waves. These observations confirm and expand on our proposed concept of the SAID channel being a turbulent boundary layer, formed via a short circuit of the substorm-injected plasmoid by the plasmasphere. We show that SAID formation is related to enhanced lower hybrid/fast magnetosonic waves. Their excitation leads to anomalous circuit resistivity and magnetic diffusion, similar to the well-documented plasmoid-magnetic barrier problem, including impulsive penetration at the magnetopause.

Abstract.Observations of airglow at 630 nm (red line) and 557.7 nm (green line) during HF modification experiments at the High Frequency Active Auroral Research Program (HAARP) heating facility are analyzed. We propose a theoretical framework for understanding the generation of Langmuir and ion acoustic waves during magnetic zenith injections. We show that observations of HF-induced airglow in an underdense ionosphere as well as a decrease in the height of the emitting volume are consistent with this scenario.

[1] We report on ground magnetic and optical observations performed during an ionospheric heating experiment at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska on 29 October 2008. The experiment was aimed at generation of large-amplitude ULF electromagnetic waves by triggering and facilitating development of the ionospheric feedback instability (IFI) in the region adjacent to a bright auroral arc. In this region the downward/return magnetic field-aligned current decreases plasma density and enhances the electric field in the ionosphere. A combination of these two effects creates favorable conditions for the instability. The experiment occurred during a period of substorm activity, but effects from the HAARP transmitter were not sufficiently intense to be detected against the background of strong natural oscillations occurring farther north from the HAARP site. Thus the experiment did not provide concrete evidence that heating of the ionosphere with powerful HF transmitters can affect IFI development or generate intense ULF electromagnetic waves. However, during the experiment ground-based magnetometers in Alaska and Canada detected large-amplitude ULF waves in regions where the substorm onset auroral arcs interacted with the ionosphere. The frequencies of these waves closely matched frequencies predicted by simulations of IFI for these particular geophysical conditions. These observations support the hypothesis that geomagnetic substorms, the corresponding dynamics of discrete auroral arcs, and the ionospheric feedback instability are closely connected phenomena.Citation: Streltsov, A. V., T. R. Pedersen, E. V. Mishin, and A. L. Snyder (2010), Ionospheric feedback instability and substorm development,

Abstract.Outshifted I)lasma lines, observed during injections of intense HF ra(tiowaves into the io•osphere, are due to scattering on Langlnuir waves with an unusually large spectral widi, h shifted above the injected frequency. Incoherent scatter radar observations reveal that these waves sometimes are located at altitudes exceeding by several kilolneters the altitude of the reflection layer of the ordinary HF wave, titus making an explanation in terlns of the so-called "free mode" problematic. We show that these ol•servations may be consistently described by the creation, (lue to the ponderomotive force, of density depletions in the Airy pattern of the Z i•to(le. Tlte geileration of Langmuir plasmons by accelerated suprathermal electrons i•tside the depletions causes the wide spectral width of these plasma line features and their Inean frequency shift.