M. J. Keskinen

Two components of ionospheric plasma structuring at midlatitudes observed during the large magnetic storm of October 30, 2003

[1]xa0We consider VHF amplitude scintillations, GPS phase fluctuations, ionosonde measurements, maps of GPS total electron content (TEC), observations of daytime aurora and TIMED GUVI images during the large magnetic storms of October 29–31, 2003, and find two distinct classes of plasma processes that produce midlatitude ionospheric irregularities. One is associated with auroral plasma processes; the other, with storm enhanced density (SED) gradients, a part of which occur in close proximity to sub-auroral polarization stream (SAPS) electric fields as discussed by J. C. Foster et al. (2002). We analyze in detail the storm event of October 30, 2003. The SAPS-associated plasma structures may occur by an ion temperature gradient convective instability (M. J. Keskinen et al., 2004), but structuring by auroral processes requires elucidation.

The WIND‐HAARP Experiment: Initial results of high power radiowave interactions with space plasmas

Results from the first science experiment with the new HF Active Auroral Research Program (HAARP) in Alaska are reported. The objective was to study the effects of space plasmas on high power radiowave transmission to high altitudes in the magnetosphere. Reception was done by the NASA/WIND satellite. The data suggest that structured space plasmas along the propagation path impose a power law spectrum of fluctuations on the transmitted waves, resembling scintillations. Because the transmitted waves are near ionospheric plasma frequencies, other types of wave-plasma interactions may occur. Such measurements can provide a new diagnostic tool.

Ion gyroradius‐sized structures and artificial ion conics generated by the Arecibo ionospheric heater

A model for ionospheric density structures at the O+ ion gyroradius induced by the Arecibo heater during the recent El Coqui campaign has been developed. We find that (1) these density structures can be accounted for by the parametric decay of the high frequency high power Arecibo heater wave into a low frequency wave with frequency at or near the ion cyclotron frequency and high frequency sideband modes (2) the growth rate of this process peaks at scale sizes corresponding to the O+ ion gyroradius (3) computed density fluctuations, using a strong turbulence model, associated with the ion cyclotron modes, in the nonlinear regime, are in the range of 2–12% and (4) anisotropic ion-conic-like heating will result from this process. The results of this model are in good agreement with recent El Coqui observations.

A wave interference experiment with HAARP, HIPAS, and WIND

We report on the first experiment using two high power, high frequency transmitting facilities in a bistatic, interferometer mode. The HAARP and HIPAS facilities in Alaska radiated at 4525 kHz with total combined power of about 700 kW, in the direction of the WIND spacecraft. The WAVES experiment aboard WIND received the transmissions at a distance of about 25 earth radii. The experimental setup thus resembled Youngs two-slit experiment. The expected interference pattern was observed; at the distance of WIND, the fringe size was about 30 km peak to peak.

Nonlinear unstable auroral-arc driven thermospheric winds in an ionosphere-magnetosphere coupled model

The nonlinear evolution of thermospheric winds in an ionosphere-magnetosphere coupled model has been studied for the first time for a dynamic unstable auroral-arc environment. We treat the problem using a multi-layer, quasi-three-dimensional model which averages in altitude the thermospheric dynamics over each layer. For the upper thermosphere, we find that (1) the thermosphere can respond to the ionospheric Kelvin-Helmholtz (KH) instability on temporal scales on the order of an hour, depending on ambient conditions, and on spatial scales of tens to hundreds of kilometers, (2) strong thermospheric meridional and zonal vortical flows with embedded nonlinear jet-like structures can be generated by the ionospheric/magnetospheric KH instability and (3) neutral thermospheric winds, vortices, and associated power spectra develop in a distinctly different manner in the presence of magnetospheric coupling effects. Comparison with recent observations is made.

A low-altitude mechanism for mesoscale dynamics, structure, and current filamentation in the discrete aurora

The two-dimensional nonlinear evolution of the ionization-driven adiabatic auroral arc instability has been studied for the first time. We find: (1) the adiabatic auroral arc instability can fully develop on time scales of tens to hundreds of seconds and on spatial scales of tens to hundreds of kilometers, (2) the evolution of this instability leads to nonlinear “hook-shaped” conductivity structures, (3) this instability can lead to parallel current filamentation over a wide range of scale sizes from kΛ0 1 where k is the wavenumber and Λ0 is the initial arc width perpendicular to the geomagnetic field, and (4) the k-spectra of the density, electric field, and parallel current develop into inverse power laws in agreement with satellite observations. Comparison with mesoscale auroral phenomenology and current filamentation structures is made