O+phase bunching as a source for stable auroral arcs
| Autor: | Lars P. Block, Michael B. Silevitch, Paul L. Rothwell, Carl-Gunne Fälthammar |
|---|---|
| Rok vydání: | 2000 |
| Předmět: |
Atmospheric Science
Soil Science Magnetosphere Aquatic Science Oceanography Alfvén wave Optics Geochemistry and Petrology Substorm Earth and Planetary Sciences (miscellaneous) Earth-Surface Processes Water Science and Technology Physics Ecology business.industry Paleontology Forestry Polarization (waves) Computational physics Solar wind Wavelength Geophysics Space and Planetary Science Physics::Space Physics Ionosphere business Striation |
| Zdroj: | Journal of Geophysical Research: Space Physics. 105:10739-10749 |
| ISSN: | 0148-0227 |
| DOI: | 10.1029/1999ja900360 |
| Popis: | We propose a model to explain how ion dynamics create an Alfven wave generator in the equatorial region that can be applied to the stable arc problem. For example, in the earthward drifting magnetotail plasma, phase bunching of O+ ions (and to a much lesser extent of the H+ ions) can be caused by a weak (∼1×10−9 Vm−2) electric field gradient [Rothwell et al., 1994]. This leads to density striations in the GSM frame. O+ density striations in the earthward drifting plasma frame are seen as a tailward propagating source of Alfven waves where the hydrogen ions provide the polarization current of the wave. A transformation to the GSM frame will yield a static, oblique wave structure similar to that previously treated. The waves propagate from the equatorial region to both ionospheres where they are reflected. The ionospheric boundary condition when combined with a magnetospheric boundary condition allows a solution of the wave amplitudes in terms of the striation structure. The frequency of the Alfven wave and the associated wavelengths are also determined by the striation driver. We find that the magnitude of the parallel current density at the ionosphere has a spatial resonance when the distance between the ionosphere and the equatorial plane is equal to a quarter wavelength along Bo. In that case, the magnitude of the parallel current density at the ionosphere is of the order of 10 μA m−2 and peaks for striation wavelengths (as mapped to the ionosphere) of 10–40 km, which is comparable to the transverse scale of auroral arcs. The associated Poynting flux incident on the ionosphere is found to be ∼ 2 mWm−2 and represents a net transfer of energy from the magnetosphere to the ionosphere as recently observed by experimenters studying substorm onsets. We find that in the steady state the power extracted from the bulk flow to power the arc is balanced by energy provided by the solar wind through the cross-tail electric field. |
| Databáze: | OpenAIRE |
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