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| Titel |
Modulation of ionospheric conductance and electric field associated with pulsating aurora |
| VerfasserIn |
Keisuke Hosokawa, Yasunobu Ogawa, Akira Kadokura, Hiroshi Miyaoka, Natsuo Sato |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033654
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| Zusammenfassung |
| We present, for the first time, a quasi-periodic modulation of ionospheric parameters,
associated with the occurrence of pulsating auroras, such as electron density, conductance,
and electric field. In March 2008, simultaneous campaign-based measurements of pulsating
auroras were conducted over Tromsoe (69.60N, 19.20E), Norway, using an all-sky TV
camera (ATV) and the EISCAT UHF system. During an interval within this campaign period,
pulsating auroras, with periods of 8-17 s, were observed by the ATV in the morning local
time sector (approximatelly 05 MLT). In this interval, quasi-periodic oscillations were
identified in the raw electron density obtained by EISCAT. The electron density at lower
altitudes in the E region (95-115 km) was enhanced by a factor of 3-4 immediately after the
optical pulsation became "on". The height-integrated Hall conductance was also elevated by a
factor of 1.5-2 almost in harmony with the electron density variation. The response of the
electron density and Hall conductance to the appearance of the pulsating aurora was
almost immediate. However, both did not decrease to the background level promptly
after optical pulsation ceased. This was primarily because it took a few seconds
for the electron density to decrease through recombination with ambient ions at
these altitudes. Interestingly, electric field measurements performed by the remote
antenna at Kiruna showed that redirection of the electric field occurred when the
pulsating aurora was "on". We propose a model in which the enhancement of Hall
conductance within patches of the pulsating aurora caused charge accumulation at
the edges of the patches, and the electric field was then modified by the resulting
polarization electric field. An estimation of the electric field modulation with this
model well reproduced the actual electric field observations carried out by EISCAT,
which confirmed the validity of the model. These results imply that the ionization
caused by high-energy electron precipitation associated with a pulsating aurora has a
significant effect on the ionospheric conductivity and current system. This modification
of the ionosphere may facilitate characterization of the morphological features
of pulsating auroras. In particular, modification of the electric field would affect
the spatial structure of pulsating aurora patches, such as their motion and shapes. |
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