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| Titel |
Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets |
| VerfasserIn |
C. E. Valladares, D. Alcaydé, J. V. Rodriguez, J. M. Ruohoniemi, A. P. Eyken |
| 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 ; 17, no. 8 ; Nr. 17, no. 8, S.1020-1039 |
| Datensatznummer |
250013797
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| Publikation (Nr.) |
 copernicus.org/angeo-17-1020-1999.pdf |
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| Zusammenfassung |
We report important results of the first
campaign specially designed to observe the formation and the initial convection
of polar cap patches. The principal instrumentation used in the experiments
comprised the EISCAT, the Sondrestrom, and the Super DARN network of radars. The
experiment was conducted on February 18, 1996 and was complemented with
additional sensors such as the Greenland chain of magnetometers and the WIND and
IMP-8 satellites. Two different types of events were seen on this day, and in
both events the Sondrestrom radar registered the formation and evolution of
large-scale density structures. The first event consisted of the passage of
traveling convection vortices (TCV). The other event occurred in association
with the development of large plasma jets (LPJ) embedded in the sunward
convection part of the dusk cell. TCVs were measured, principally, with the
magnetometers located in Greenland, but were also confirmed by the line-of-sight
velocities from the Sondrestrom and SuperDARN radars. We found that when the
magnetic perturbations associated with the TCVs were larger than 100 nT, then a
section of the high-latitude plasma density was eroded by a factor of 2. We
suggest that the number density reduction was caused by an enhancement in the O+
recombination due to an elevated Ti, which was produced by the much
higher frictional heating inside the vortex. The large plasma jets had a
considerable (>1000 km) longitudinal extension and were 200-300 km in width.
They were seen principally with the Sondrestrom, and SuperDARN radars. Enhanced
ion temperature (Ti) was also observed by the Sondrestrom and EISCAT
radars. These channels of high Ti were exactly collocated with the
LPJs and some of them with regions of eroded plasma number density. We suggest
that the LPJs bring less dense plasma from later local times. However, the
recent time history of the plasma flow is important to define the depth of the
density depletion. Systematic changes in the latitudinal location and in the
intensity of the LPJs were observed in the 2 min time resolution data of the
SuperDARN radars. The effect of the abrupt changes in the LPJs location is to
create regions containing dayside plasma almost detached from the rest of the
oval density. One of these density features was seen by the Sondrestrom radar at
1542 UT. The data presented here suggest that two plasma structuring mechanisms
(TCVs and LPJs) can act tens of minutes apart to produce higher levels of
density structures in the near noon F-region ionosphere.
Key words. Ionosphere (ionospheric irregularities) ·
Magnetospheric physics (electric fields; polar cap phenomena) |
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