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| Titel |
Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields |
| VerfasserIn |
R. Shi, D. Han, B. Ni, Z.-J. Hu, C. Zhou, X. Gu |
| 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 ; 30, no. 9 ; Nr. 30, no. 9 (2012-09-03), S.1297-1307 |
| Datensatznummer |
250017262
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| Publikation (Nr.) |
 copernicus.org/angeo-30-1297-2012.pdf |
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| Zusammenfassung |
| Compared to the recently improved understanding of nightside diffuse aurora,
the mechanism(s) responsible for dayside diffuse aurora remains poorly
understood. While dayside chorus has been thought as a potential major
contributor to dayside diffuse auroral precipitation, quantitative analyses
of the role of chorus wave scattering have not been carefully performed. In
this study we investigate a dayside diffuse auroral intensification event
observed by the Chinese Arctic Yellow River Station (YRS) all-sky imagers
(ASI) on 7 January 2005 and capture a substantial increase in diffuse
auroral intensity at the 557.7 nm wavelength that occurred over almost the
entire ASI field-of-view near 09:24 UT, i.e., ~12:24 MLT. Computation
of bounce-averaged resonant scattering rates by dayside chorus emissions
using realistic magnetic field models demonstrates that dayside chorus
scattering can produce intense precipitation losses of plasma sheet
electrons on timescales of hours (even approaching the strong diffusion
limit) over a broad range of both energy and pitch angle, specifically, from
~1 keV to 50 keV with equatorial pitch angles from the loss cone to up
to ~85° depending on electron energy. Subsequent estimate of loss
cone filling index indicates that the loss cone can be substantially filled,
due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8
for electrons from ~500 eV to 50 keV that exactly covers the
precipitating electrons for the excitation of green-line diffuse aurora.
Estimate of electron precipitation flux at different energy levels, based on
loss cone filling index profile and typical dayside electron distribution
observed by THEMIS spacecraft under similar conditions, gives a total
precipitation electron energy flux of the order of 0.1 erg cm−2 s−1 with
~1 keV characteristic energy (especially when using T01s), which can
be very likely to cause intense green-line diffuse aurora activity on the
dayside. Therefore, dayside chorus scattering in the realistic magnetic
field can greatly contribute to the YRS ASI observed intensification of
dayside green-line aurora. Besides wave induced scattering and changes in
the ambient magnetic field, variations in associated electron flux can also
contribute to enhanced diffuse aurora emissions, the possibility of which we
cannot exactly rule out due to lack of simultaneous observations of
magnetospheric particles. Since the geomagnetic activity level was rather
low during the period of interest, it is reasonable to infer that changes in
the associated electron flux in the magnetosphere should be small, and
consequently its contribution to the observed enhanced diffuse auroral
activity should be small as well. Our results support the scenario that
dayside chorus could play a major role in the production of dayside diffuse
aurora, and also demonstrate that changes in magnetospheric magnetic field
should be considered to reasonably interpret observations of dayside diffuse
aurora. |
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