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| Titel |
Statistical properties of Joule heating rate, electric field and conductances at high latitudes |
| VerfasserIn |
A. T. Aikio, A. Selkälä |
| 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 ; 27, no. 7 ; Nr. 27, no. 7 (2009-07-06), S.2661-2673 |
| Datensatznummer |
250016579
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2661-2009.pdf |
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| Zusammenfassung |
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
Kp dependence of parameters with high temporal and spatial resolution.
All the parameters show a clear MLT variation, which is different for low and
high Kp 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 Kp≥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.
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 (Kp<3 and Kp≥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. |
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