Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere
A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (<i>K<sub>p</sub></i> = 7- and IMF<i> B<sub>z</sub></i> < 0). The ionosondes measured electron densities of up to 9 × 10<sup>11<...
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| Language: | English |
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Copernicus Publications
1999-04-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/17/463/1999/angeo-17-463-1999.pdf |
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| author | P. Prikryl J. W. MacDougall I. F. Grant I. F. Grant D. P. Steele G. J. Sofko R. A. Greenwald |
| author_facet | P. Prikryl J. W. MacDougall I. F. Grant I. F. Grant D. P. Steele G. J. Sofko R. A. Greenwald |
| author_sort | P. Prikryl |
| collection | DOAJ |
| description | A long series of polar patches was observed
by ionosondes and an all-sky imager during a disturbed period (<i>K<sub>p</sub></i>
= 7- and IMF<i> B<sub>z</sub></i> < 0). The ionosondes measured electron
densities of up to 9 × 10<sup>11</sup> m<sup>-3</sup> 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<i> B<sub>y</sub></i> > 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<i> B<sub>y</sub></i>)
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.<br><br><b>Key words.</b> Ionosphere (polar ionosphere). Magneto-
spheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere
interactions). |
| first_indexed | 2024-12-23T11:36:29Z |
| format | Article |
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| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-23T11:36:29Z |
| publishDate | 1999-04-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-a8a68d18432b4bfbae6a65b4e64bc8e72022-12-21T17:48:38ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05761999-04-011746348910.1007/s00585-999-0463-0Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphereP. Prikryl0J. W. MacDougall1I. F. Grant2I. F. Grant3D. P. Steele4G. J. Sofko5R. A. Greenwald6Communications Research Centre, 3701 Carling Ave., Box 11490, Station H, Ottawa, Ont. K2H 8S2, CanadaDepartment of Physics and Astronomy, University of Western Ontario, London, Ont. N6A 5B9, CanadaDepartment of Physics and Astronomy, University of Western Ontario, London, Ont. N6A 5B9, CanadaPresent address: CSIRO Division of Atmospheric Research, Aspendale, VIC 3195, AustraliaInstitute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Sask. S7N 5E2, CanadaInstitute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Sask. S7N 5E2, CanadaThe Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USAA long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (<i>K<sub>p</sub></i> = 7- and IMF<i> B<sub>z</sub></i> < 0). The ionosondes measured electron densities of up to 9 × 10<sup>11</sup> m<sup>-3</sup> 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<i> B<sub>y</sub></i> > 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<i> B<sub>y</sub></i>) 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.<br><br><b>Key words.</b> Ionosphere (polar ionosphere). Magneto- spheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere interactions).https://www.ann-geophys.net/17/463/1999/angeo-17-463-1999.pdf |
| spellingShingle | P. Prikryl J. W. MacDougall I. F. Grant I. F. Grant D. P. Steele G. J. Sofko R. A. Greenwald Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere Annales Geophysicae |
| title | Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| title_full | Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| title_fullStr | Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| title_full_unstemmed | Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| title_short | Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere |
| title_sort | observations of polar patches generated by solar wind alfven wave coupling to the dayside magnetosphere |
| url | https://www.ann-geophys.net/17/463/1999/angeo-17-463-1999.pdf |
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