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| Titel |
Sq field characteristics at Phu Thuy, Vietnam, during solar cycle 23: comparisons with Sq field in other longitude sectors |
| VerfasserIn |
H. Pham Thi Thu, C. Amory-Mazaudier, M. Huy |
| 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 ; 29, no. 1 ; Nr. 29, no. 1 (2011-01-04), S.1-17 |
| Datensatznummer |
250016943
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1-2011.pdf |
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| Zusammenfassung |
Quiet days variations in the Earth's magnetic field (the Sq current system)
are compared and contrasted for the Asian, African and American sectors
using a new dataset from Vietnam. This is the first presentation of the
variation of the Earth's magnetic field (Sq), during the solar cycle 23, at
Phu Thuy, Vietnam (geographic latitudes 21.03° N and longitude: 105.95° E).
Phu Thuy observatory is located below the crest of the equatorial fountain
in the Asian longitude sector of the Northern Hemisphere. The morphology of
the Sq daily variation is presented as a function of solar cycle and
seasons. The diurnal variation of Phu Thuy is compared to those obtained in
different magnetic observatories over the world to highlight the
characteristics of the Phu Thuy observations. In other longitude sectors we
find different patterns.
At Phu Thuy the solar cycle variation of the amplitude of the daily
variation of the X component is correlated to the F.10.7 cm solar radiation
(~0.74). This correlation factor is greater than the correlation
factor obtained in two observatories located at the same magnetic latitudes
in other longitude sectors: at Tamanrasset in the African sector (~0.42,
geographic latitude ~22.79) and San Juan in the American sector
(~0.03, geographic latitude ~18.38).
At Phu Thuy, the Sq field exhibits an equinoctial and a diurnal asymmetry:
– The seasonal variation of the monthly mean of X component exhibits the
well known semiannual pattern with 2 equinox maxima, but the X component is
larger in spring than in autumn. Depending of the phase of the sunspot
cycle, the maximum amplitude of the X component varies in spring from 30 nT
to 75 nT and in autumn from 20 nT to 60 nT. The maximum amplitude of the X
component exhibits roughly the same variation in both solstices, varying
from about ~20 nT to 50 nT, depending on the position into the solar
cycle.
– In all seasons, the mean equinoctial diurnal Y component has a morning
maximum
Larger than the afternoon minimum i.e. the equivalent current flow over a
day is more southward than northward. During winter, the asymmetry is
maximum, it erases the afternoon minimum. At the Gnangara observatory, in
Asian Southern Hemisphere, the diurnal Y pattern is opposite and the current
flow is more northward.
It seems that in the Asian sector, the northern and southern Sq current
cells both contribute strongly to the equatorial electrojet. The pattern is
different in the African and American sectors where the northern Sq current
cell contribution to the equatorial electrojet is smaller than the southern
one. These observations can explain the unexpected maximum of amplitude of
the equatorial electrojet observed in the Asian sector where the internal
field is very large. During winter the Y component flow presents an anomaly,
it is always southward during the whole day and there is no afternoon
northward circulation. |
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