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| Titel |
Estimation of ionospheric electric fields using modelling of metastable auroral emissions |
| VerfasserIn |
S. Tuttle, B. Lanchester, B. Gustavsson, N. Ivchenko |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068837
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| Zusammenfassung |
| A method of modelling small scale aurora in the magnetic zenith using radar and optical
observations has been developed and is used to examine the background ionospheric electric
field during the afterglow of an auroral event. Optical observations were obtained using the
Auroral Structure and Kinetics (ASK) instrument whilst radar observations were obtained
using the EISCAT UHF radar, located in Ramfjorden, Norway. ASK is a platform of 3
co-aligned EMCCD cameras, each equipped with a narrow passband filter centred
on auroral emissions at 562.0Â nm, 732.0Â nm and 777.4Â nm. ASK is capable of
making high spatial, 20Â m at 100Â km, and temporal, up to 32 frames per second,
resolution measurements of the aurora and was co-located with the radar for these
observations. Both instruments were observing in the magnetic zenith. The radar
measurements are used to estimate the energy spectra of the precipitating elections. The
energy spectra are used as input to an ion-chemistry model to model the production
profiles of atmospheric species which contribute to the aurora. A look-up table
characterising each production profile in terms of an energy and flux estimate, obtained
from the ASK observations, is produced. The look-up table allows the production
profiles to be extrapolated outside the radar field of view to cover the ASK field of
view.
For prompt emissions, such as the 562.0Â nm and 777.4Â nm emissions, the lifetime of the
excited state is so short that the emission rate is the production rate. The 732.0Â nm
emission, which selects emissions from the O+(2P) ion, does not emit promptly
and has an altitude dependent lifetime of up to 5Â seconds. In the presence of an
electric field, the ion will drift from the location it was produced. The continuity
equation for O+(2P) ions is used to calculate the emission rate of O+(2P) ions,
taking into account quenching and drift. Modelled images of the aurora are produced
by projecting the emission rates to an image plane on the ground. Comparing the
observed 732.0Â nm emission to the modelled O+(2P) emission allows the drift velocity
which gives the closest match to be found. The electric field is then calculated using
the E x B drift. Further development of this model will allow the investigation
of the electrodynamics of auroral arcs whilst auroral precipitation is occurring. |
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