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| Titel |
Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| VerfasserIn |
P. Prikryl, J. W. MacDougall, I. F. Grant, D. P. Steele, G. J. Sofko, R. A. Greenwald |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 17, no. 4 ; Nr. 17, no. 4, S.463-489 |
| Datensatznummer |
250013709
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| Publikation (Nr.) |
 copernicus.org/angeo-17-463-1999.pdf |
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| Zusammenfassung |
A long series of polar patches was observed
by ionosondes and an all-sky imager during a disturbed period (Kp
= 7- and IMF Bz < 0). The ionosondes measured electron
densities of up to 9 × 1011 m-3 in the patch center, an
increase above the density minimum between patches by a factor of \sim4.5. Bands
of F-region irregularities generated at the equatorward edge of the patches were
tracked by HF radars. The backscatter bands were swept northward and eastward
across the polar cap in a fan-like formation as the afternoon convection cell
expanded due to the IMF By > 0. Near the north magnetic
pole, an all-sky imager observed the 630-nm emission patches of a distinctly
band-like shape drifting northeastward to eastward. The 630-nm emission patches
were associated with the density patches and backscatter bands. The patches
originated in, or near, the cusp footprint where they were formed by convection
bursts (flow channel events, FCEs) structuring the solar EUV-produced
photoionization and the particle-produced auroral/cusp ionization by segmenting
it into elongated patches. Just equatorward of the cusp footprint Pc5 field line
resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars.
The AC electric field associated with the FLRs resulted in a
poleward-progressing zonal flow pattern and backscatter bands. The VHF radar
Doppler spectra indicated the presence of steep electron density gradients
which, through the gradient drift instability, can lead to the generation of the
ionospheric irregularities found in patches. The FLRs and FCEs were associated
with poleward-progressing DPY currents (Hall currents modulated by the IMF By)
and riometer absorption enhancements. The temporal and spatial characteristics
of the VHF backscatter and associated riometer absorptions closely resembled
those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8
observed large amplitude Alfvén waves that were correlated with Pc5 pulsations
observed by the ground magnetometers, riometers and radars. It is concluded that
the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves
coupling to the dayside magnetosphere. During a period of southward IMF the
dawn-dusk electric field associated with the Alfvén waves modulated the
subsolar magnetic reconnection into pulses that resulted in convection flow
bursts mapping to the ionospheric footprint of the cusp.
Key words. Ionosphere (polar ionosphere). Magneto-
spheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere
interactions). |
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