Statistical properties of Joule heating rate, electric field and conductances at high latitudes
Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat) from 6 March to 6 April 2006. The data are from the same season (close to...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2009-07-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/2661/2009/angeo-27-2661-2009.pdf |
| _version_ | 1811220840818147328 |
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| author | A. T. Aikio A. Selkälä |
| author_facet | A. T. Aikio A. Selkälä |
| author_sort | A. T. Aikio |
| collection | DOAJ |
| description | Statistical properties of Joule heating rate, electric field and conductances
in the high latitude ionosphere are studied by a unique one-month measurement
made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat) from 6
March to 6 April 2006. The data are from the same season (close to vernal
equinox) and from similar sunspot conditions (about 1.5 years before the
sunspot minimum) providing an excellent set of data to study the MLT and
<I>K<sub>p</sub></I> dependence of parameters with high temporal and spatial resolution.
<br><br>
All the parameters show a clear MLT variation, which is different for low and
high <I>K<sub>p</sub></I> conditions. Our results indicate that the response of morning
sector conductances and conductance ratios to increased magnetic activity is
stronger than that of the evening sector. The co-location of Pedersen
conductance maximum and electric field maximum in the morning sector produces
the largest Joule heating rates 03–05 MLT for <I>K<sub>p</sub></I>≥3. In the evening
sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in
the nightside are statistically observed at 23 MLT, which is the location of
the electric Harang discontinuity.
<br><br>
An important outcome of the paper are the fitted functions for the Joule
heating rate as a function of electric field magnitude, separately for four
MLT sectors and two activity levels (<I>K<sub>p</sub></I><3 and <I>K<sub>p</sub></I>≥3). In addition to
the squared electric field, the fit includes a linear term to study the
possible anticorrelation or correlation between electric field and
conductance. In the midday sector, positive correlation is found as well as
in the morning sector for the high activity case. In the midnight and evening
sectors, anticorrelation between electric field and conductance is obtained,
i.e. high electric fields are associated with low conductances. This is
expected to occur in the return current regions adjacent to auroral arcs as a
result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004)
In addition, a part of the anticorrelation may come from polarization effects
inside high-conductance regions, e.g. auroral arcs. These observations
confirm the speculated effect of small scale electrodynamics, which is not
included in most of the global modeling efforts of Joule heating rate. |
| first_indexed | 2024-04-12T07:48:42Z |
| format | Article |
| id | doaj.art-1a1068789c15424c8e9a1dd7e089b816 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-04-12T07:48:42Z |
| publishDate | 2009-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-1a1068789c15424c8e9a1dd7e089b8162022-12-22T03:41:38ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762009-07-01272661267310.5194/angeo-27-2661-2009Statistical properties of Joule heating rate, electric field and conductances at high latitudesA. T. Aikio0A. Selkälä1Department of Physics, University of Oulu, P.O. Box 3000, 90014, FinlandDepartment of Physics, University of Oulu, P.O. Box 3000, 90014, FinlandStatistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat) from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox) and from similar sunspot conditions (about 1.5 years before the sunspot minimum) providing an excellent set of data to study the MLT and <I>K<sub>p</sub></I> dependence of parameters with high temporal and spatial resolution. <br><br> All the parameters show a clear MLT variation, which is different for low and high <I>K<sub>p</sub></I> conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for <I>K<sub>p</sub></I>≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity. <br><br> An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (<I>K<sub>p</sub></I><3 and <I>K<sub>p</sub></I>≥3). In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to auroral arcs as a result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004) In addition, a part of the anticorrelation may come from polarization effects inside high-conductance regions, e.g. auroral arcs. These observations confirm the speculated effect of small scale electrodynamics, which is not included in most of the global modeling efforts of Joule heating rate.https://www.ann-geophys.net/27/2661/2009/angeo-27-2661-2009.pdf |
| spellingShingle | A. T. Aikio A. Selkälä Statistical properties of Joule heating rate, electric field and conductances at high latitudes Annales Geophysicae |
| title | Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| title_full | Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| title_fullStr | Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| title_full_unstemmed | Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| title_short | Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| title_sort | statistical properties of joule heating rate electric field and conductances at high latitudes |
| url | https://www.ann-geophys.net/27/2661/2009/angeo-27-2661-2009.pdf |
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