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| Titel |
MT-index - a possible new index to characterize the magnetic configuration of magnetotail |
| VerfasserIn |
V. A. Sergeev, B. B. Gvozdevsky |
| 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 ; 13, no. 10 ; Nr. 13, no. 10, S.1093-1103 |
| Datensatznummer |
250012011
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| Publikation (Nr.) |
 copernicus.org/angeo-13-1093-1995.pdf |
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| Zusammenfassung |
| Existing activity indices (magnetic indices
like AE, Kp, Dst or indices based on solar
wind parameters) are poor predictors of the instantaneous magnetospheric
configuration. We suggest a new activity index – the MT-index. It is defined as
the invariant latitude of the isotropic boundary (IB) of ↑100 keV protons
reduced to the midnight meridian. This IB is a low-altitude signature of the
boundary between regions of adiabatic and chaotic regimes of particle motion in
the tail current sheet which is controlled by the magnetic field in the
equatorial near-Earth tail (at 5–10Re). We have investigated
the local time and activity dependence of the IB latitude based on data from
about 2000 orbits of NOAA spacecraft. By finding the formula to reduce the IB
latitude to midnight meridian, we then evaluate the accuracy of the derived
index. We compared the MT-index with the magnetic field measured simultaneously
by geosynchronous GOES-2 spacecraft and showed that, unlike the traditional
indices, the MT-index displays a good correlation (r↑0.9) with the
magnetic field inclination in the nightside portion of the geosynchronous orbit.
It is, thus, a good measure to characterize quantitatively the tailward
stretching of the tail magnetic field. Based on the measured MT value, a simple
numerical procedure is suggested to choose the version of the T89 magnetospheric
model. We conclude that the MT-index is the best known predictor of the
instantaneous magnetic configuration in the near-Earth magnetotail. It may be
available on a regular basis and can be implemented for scientific studies. |
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