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| Titel |
Ionospheric storms at geophysically-equivalent sites – Part 1: Storm-time patterns for sub-auroral ionospheres |
| VerfasserIn |
M. Mendillo, C. Narvaez |
| 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. 4 ; Nr. 27, no. 4 (2009-04-07), S.1679-1694 |
| Datensatznummer |
250016491
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1679-2009.pdf |
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| Zusammenfassung |
The systematic study of ionospheric storms has been conducted primarily with
groundbased data from the Northern Hemisphere. Significant progress has been
made in defining typical morphology patterns at all latitudes; mechanisms
have been identified and tested via modeling. At higher mid-latitudes (sites
that are typically sub-auroral during non-storm conditions), the processes
that change significantly during storms can be of comparable magnitudes, but
with different time constants. These include ionospheric plasma dynamics
from the penetration of magnetospheric electric fields, enhancements to
thermospheric winds due to auroral and Joule heating inputs, disturbance
dynamo electrodynamics driven by such winds, and thermospheric composition
changes due to the changed circulation patterns. The ~12° tilt of
the geomagnetic field axis causes significant longitude effects in all of
these processes in the Northern Hemisphere. A complementary series of
longitude effects would be expected to occur in the Southern Hemisphere. In
this paper we begin a series of studies to investigate the
longitudinal-hemispheric similarities and differences in the response of the
ionosphere's peak electron density to geomagnetic storms.
The ionosonde stations at Wallops Island (VA) and Hobart (Tasmania) have
comparable geographic and geomagnetic latitudes for sub-auroral locations,
are situated at longitudes close to that of the dipole tilt, and thus serve
as our candidate station-pair choice for studies of ionospheric storms at
geophysically-comparable locations. They have an excellent record of
observations of the ionospheric penetration frequency (foF2) spanning
several solar cycles, and thus are suitable for long-term studies. During
solar cycle #20 (1964–1976), 206 geomagnetic storms occurred that had Ap≥30 or Kp≥5
for at least one day of the
storm. Our analysis of average storm-time perturbations (percent deviations
from the monthly means) showed a remarkable agreement at both sites under a
variety of conditions. Yet, small differences do appear, and in systematic
ways. We attempt to relate these to stresses imposed over a few days of a
storm that mimic longer term morphology patterns occurring over seasonal and
solar cycle time spans. Storm effects versus season point to possible
mechanisms having hemispheric differences (as opposed to simply seasonal
differences) in how solar wind energy is transmitted through the
magnetosphere into the thermosphere-ionosphere system. Storm effects versus
the strength of a geomagnetic storm may, similarly, be related to patterns
seen during years of maximum versus minimum solar activity. |
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