High-latitude ionospheric currents during very quiet times: their characteristics and predictability
CHAMP passes the geographic poles at a distance of 2.7° in latitude, thus providing a large number of magnetic readings of the dynamic auroral regions. The data of these numerous overflights were used for a detailed statistical study on the level of activity. A large number of tracks wit...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2004-06-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/22/2001/2004/angeo-22-2001-2004.pdf |
| _version_ | 1828434101660549120 |
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| author | P. Ritter H. Lühr S. Maus A. Viljanen |
| author_facet | P. Ritter H. Lühr S. Maus A. Viljanen |
| author_sort | P. Ritter |
| collection | DOAJ |
| description | CHAMP passes the geographic poles at a distance of 2.7°
in latitude, thus providing a large number of magnetic readings
of the dynamic auroral regions. The data of these numerous overflights
were used for a detailed statistical study on the level of
activity. A large number of tracks with very low rms of the
residuals between the scalar field measurements and a high degree
field model were singled out over both the northern and southern
polar regions, independently. Low rms values indicate best model
fits and are therefore regarded as a measure of low activity,
although we are aware that this indicator also has its limitations.
The occurrence of quiet
periods is strongly controlled by the solar zenith angle at the geomagnetic
poles, indicating the importance of the ionospheric conductivity.
During the dark polar season, about 30% of the passes can be qualified as quiet.
The commonly used magnetic activity indices turn out not to be a reliable measure
for the activity state in the polar region. Least suitable is the <i>D<sub>st</sub></i> index, followed
by the <i>K<sub>p</sub></i>. Slightly better results are obtained with the <i>PC</i> and the IMAGE-<i>AE</i> indices.
The latter is rather effective within a time sector of ±4 hours of magnetic local
time around the IMAGE array.
<P style="line-height: 20px;">
The orientation of the interplanetary magnetic field (IMF) is an important
controlling factor for the activity. This is also supported by the prevailing
FAC distribution during quiet times, which resembles the typical NBZ
(northward <i>B<sub>z</sub></i>) pattern. In a superposed epoch analysis we show that the
merging electric field is a suitable geoeffective solar wind parameter.
Based on the size of this electric field and the solar zenith angle at the
geomagnetic poles, a prediction method for quiet auroral region periods is proposed.
This may, among others, be useful for the data selection in main field modelling approaches. |
| first_indexed | 2024-12-10T18:45:29Z |
| format | Article |
| id | doaj.art-8887c936b9ec42a4b577f2da2ed00145 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-10T18:45:29Z |
| publishDate | 2004-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-8887c936b9ec42a4b577f2da2ed001452022-12-22T01:37:31ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762004-06-01222001201410.5194/angeo-22-2001-2004High-latitude ionospheric currents during very quiet times: their characteristics and predictabilityP. Ritter0H. Lühr1S. Maus2A. Viljanen3GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, GermanyGeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, GermanyGeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, GermanyFinnish Meteorological Institute, Geophys. Res. Div., P.O. Box 503, FIN-00101 Helsinki, FinlandCHAMP passes the geographic poles at a distance of 2.7° in latitude, thus providing a large number of magnetic readings of the dynamic auroral regions. The data of these numerous overflights were used for a detailed statistical study on the level of activity. A large number of tracks with very low rms of the residuals between the scalar field measurements and a high degree field model were singled out over both the northern and southern polar regions, independently. Low rms values indicate best model fits and are therefore regarded as a measure of low activity, although we are aware that this indicator also has its limitations. The occurrence of quiet periods is strongly controlled by the solar zenith angle at the geomagnetic poles, indicating the importance of the ionospheric conductivity. During the dark polar season, about 30% of the passes can be qualified as quiet. The commonly used magnetic activity indices turn out not to be a reliable measure for the activity state in the polar region. Least suitable is the <i>D<sub>st</sub></i> index, followed by the <i>K<sub>p</sub></i>. Slightly better results are obtained with the <i>PC</i> and the IMAGE-<i>AE</i> indices. The latter is rather effective within a time sector of ±4 hours of magnetic local time around the IMAGE array. <P style="line-height: 20px;"> The orientation of the interplanetary magnetic field (IMF) is an important controlling factor for the activity. This is also supported by the prevailing FAC distribution during quiet times, which resembles the typical NBZ (northward <i>B<sub>z</sub></i>) pattern. In a superposed epoch analysis we show that the merging electric field is a suitable geoeffective solar wind parameter. Based on the size of this electric field and the solar zenith angle at the geomagnetic poles, a prediction method for quiet auroral region periods is proposed. This may, among others, be useful for the data selection in main field modelling approaches.https://www.ann-geophys.net/22/2001/2004/angeo-22-2001-2004.pdf |
| spellingShingle | P. Ritter H. Lühr S. Maus A. Viljanen High-latitude ionospheric currents during very quiet times: their characteristics and predictability Annales Geophysicae |
| title | High-latitude ionospheric currents during very quiet times: their characteristics and predictability |
| title_full | High-latitude ionospheric currents during very quiet times: their characteristics and predictability |
| title_fullStr | High-latitude ionospheric currents during very quiet times: their characteristics and predictability |
| title_full_unstemmed | High-latitude ionospheric currents during very quiet times: their characteristics and predictability |
| title_short | High-latitude ionospheric currents during very quiet times: their characteristics and predictability |
| title_sort | high latitude ionospheric currents during very quiet times their characteristics and predictability |
| url | https://www.ann-geophys.net/22/2001/2004/angeo-22-2001-2004.pdf |
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