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| Titel |
First direct evidence of meso-scale variability on ion-neutral dynamics using co-located tristatic FPIs and EISCAT radar in Northern Scandinavia |
| VerfasserIn |
A. L. Aruliah, E. M. Griffin, A. D. Aylward, E. A. K. Ford, M. J. Kosch, C. J. Davis, V. S. C. Howells, S. E. Pryse, H. R. Middleton, J. Jussila |
| 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 ; 23, no. 1 ; Nr. 23, no. 1 (2005-01-31), S.147-162 |
| Datensatznummer |
250015128
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| Publikation (Nr.) |
 copernicus.org/angeo-23-147-2005.pdf |
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| Zusammenfassung |
| This paper presents the first direct empirical evidence that mesoscale
variations in ion velocities must be taken into consideration when
calculating Joule heating and relating it to changes in ion temperatures and
momentum transfer to the neutral gas. The data come from the first tristatic
Fabry-Perot Interferometer (FPI) measurements of the neutral atmosphere
co-located with tristatic measurements of the ionosphere made by the
European Incoherent Scatter (EISCAT) radar which were carried out during the
nights of 27-28 February 2003 and 28 February until 1 March 2003. Tristatic
measurements mean that there are no assumptions of uniform wind fields and
ion drifts, nor zero vertical winds. The independent, tristatic,
thermospheric measurements presented here should provide unambiguous vector
wind information, and hence reduce the need to supplement observations with
information obtained from models of the neutral atmosphere, or with
estimates of neutral parameters derived from ionospheric measurements. These
new data can also test the assumptions used in models and in ion-neutral
interactions. The FPIs are located close to the 3 radars of the EISCAT
configuration in northern Scandinavia, which is a region well covered by a
network of complementary instruments. These provide a larger scale context
within which to interpret our observations of mesoscale variations on the
scales of tens of kilometres spatially and minutes temporally. Initial
studies indicate that the thermosphere is more dynamic and responsive to
ionospheric forcing than expected. Calculations using the tristatic volume
measurements show that the magnitude of the neutral wind dynamo contribution
was on average 29% of Joule heating during the first night of
observation. At times it either enhanced or reduced the effective electric
field by up to several tens of percent. The tristatic experiment also
presents the first validation of absolute temperature measurements from a
common volume observed by independently calibrated FPIs. Comparison of
EISCAT ion temperatures at an altitude of 240km with FPI neutral
temperatures show that Ti was around 200K below Tn for nearly 3h on the
first night during a period of strong geomagnetic activity. This is
inconsistent with energy transfer. Comparison with FPI temperatures from
surrounding regions indicate that it could not be accounted for by height
variations. Indeed, these first results seem to indicate that the 630-nm
emission did not stray too far from 240km. There were also apparent drops in
Te at the same time as the anomalous Ti values which are energetically
implausible. Incorrect assumptions of composition or non-Maxwellian spectra
are likely to be the problem. |
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