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| Titel |
A descent of the aurora over Lapland |
| VerfasserIn |
Daniel Whiter, Noora Partamies |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094293
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| Publikation (Nr.) |
 EGU/EGU2014-9697.pdf |
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| Zusammenfassung |
| A very large statistical study (-ă 4 x 105 measurements) into the peak emission height of the
aurora has shown that the aurora over Lapland descended significantly between 1996 and
2007. The study was performed using images from a network of ground-based
all-sky cameras which form part of the MIRACLE (Magnetometers–Ionospheric
Radar–All-sky Cameras Large Experiment) network, and are located at various
observation stations across northern Finland and Sweden. The height of the aurora
was first measured about a century ago. Since then, it has generally been assumed
that the peak emission height of any particular auroral emission is constant for
similar geomagnetic conditions. The present work was motivated by the need to
improve estimates of the height of the aurora used to calculate other ionospheric
and auroral properties, such as optical flow velocities and auroral arc widths. In
recent years MIRACLE has produced approximately 105 images of the aurora per
station per year. In order to analyse such a large number of images, a novel fast and
automatic method was developed for finding the peak emission height of an auroral
structure from a pair of all-sky camera images with overlapping fields of view.
This method has been applied to all auroral images recorded by the MIRACLE
intensified CCD cameras in operation between 1996 and 2007. Such a large data set
allows the study of variations in the height of the aurora with time (yearly, monthly,
hourly) and with solar and geomagnetic indices such as F10.7 and Kp. Results
from the statistical study show that the peak emission height of green (557.7nm,
O1S–O1D transition) aurora over Lapland descended by about 10km between 1996 and
2007. This descent occurred independently of the solar cycle, and is thought to
be due to a cooling and contraction of the mesosphere and lower thermosphere. |
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