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| Titel |
An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations |
| VerfasserIn |
V. V. Lobzin, A. V. Pavlov, N. M. Pavlova |
| 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 ; 17, no. 11 ; Nr. 17, no. 11, S.1411-1425 |
| Datensatznummer |
250013834
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| Publikation (Nr.) |
 copernicus.org/angeo-17-1411-1999.pdf |
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| Zusammenfassung |
This study compares the Isis II satellite
measurements of the electron density and temperature, the integral airglow
intensity and volume emission rate at 630 nm in the SAR arc region, observed at
dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the
geomagnetic storm. The model results were obtained using the time dependent
one-dimensional mathematical model of the Earth's ionosphere and plasmasphere
(the IZMIRAN model). The major enhancement to the IZMIRAN model developed in
this study to explain the two component 630 nm emission observed is the
analytical yield spectrum approach to calculate the fluxes of precipitating
electrons and the additional production rates of N+2, O+2,
O+(4S), O+(2D), O–(2P),
and O+(2P) ions, and O(1D) in the
SAR arc regions in the Northern and Southern Hemispheres. In order to bring the
measured and modelled electron temperatures into agreement, the additional
heating electron rate of 1.05 eV cm–3 s–1 was added in the
energy balance equation of electrons at altitudes above 5000 km during the main
phase of the geomagnetic storm. This additional heating electron rate determines
the thermally excited 630 nm emission observed. The IZMIRAN model calculates a
630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral
intensity of 8.1 kR, values which are slightly lower compared to the observed
4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be
explained considering both the soft energy electron excited component and the
thermally excited component. It is found that the inclusion of N2(v
> 0) and O2(v > 0) in the calculations of the O+(4S)
loss rate improves the agreement between the calculated Ne and the
data on 4 August, 1972. The
N2(v > 0) and O2(v > 0) effects are
enough to explain the electron density depression in the SAR arc F-region and
above F2 peak altitude. Our calculations show that the increase in the O++N2
rate factor due to the vibrationally excited nitrogen produces the 5–19%
reductions in the calculated quiet daytime peak density and the 16–24% decrease
in NmF2 in the SAR arc region. The increase in the O++N2
loss rate due to vibrationally excited O2 produces the 7–26% decrease
in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in
the SAR arc region. We evaluated the role of the electron cooling rates by
low-lying electronic excitation of O2(a1Δg)
and O2(b1Σg+),
and rotational excitation of O2, and found that the effect of these
cooling rates on Te can be considered negligible during the
quiet and geomagnetic storm period 3-4 August, 1972. The energy exchange between
electron and ion gases, the cooling rate in collisions of O(3P)
with thermal electrons with excitation of O(1D), and the
electron cooling rates by vibrational excitation of O2 and N2
are the largest cooling rates above 200 km in the SAR arc region on 4 August,
1972. The enhanced IZMIRAN model calculates also number densities of N2(B3Πg+),N2(C3Πu),
and N2(A3Σu+)
at several vibrational levels, O(1S), and the volume emission
rate and integral intensity at 557.7 nm in the region between 120 and 1000 km.
We found from the model that the integral intensity at 557.7 nm is much less
than the integral intensity at 630 nm.
Key words. Atmospheric composition and structure
(airglow and aurora; thermosphere – composition and chemistry) · Ionosphere
(ionosphere – magnetosphere interactions) |
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