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| Titel |
The combined effects of electrojet strength and the geomagnetic activity (Kp-index) on the post sunset height rise of the F-layer and its role in the generation of ESF during high and low solar activity periods |
| VerfasserIn |
S. Tulasi Ram, P. V. S. Rama Rao, D. S. V. V. D. Prasad, K. Niranjan, A. Raja Babu, R. Sridharan, C. V. Devasia, Sudha Ravindran |
| 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 ; 25, no. 9 ; Nr. 25, no. 9 (2007-10-02), S.2007-2017 |
| Datensatznummer |
250015915
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2007-2007.pdf |
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| Zusammenfassung |
Several investigations have been carried out to identify the factors that
are responsible for the day-to-day variability in the occurrence of
equatorial spread-F (ESF). But the precise forecasting of ESF on a
day-to-day basis is still far from reality. The nonlinear development and
the sustenance of ESF/plasma bubbles is decided by the background
ionospheric conditions, such as the base height of the F-layer (h'F), the
electron density gradient (dN/dz), maximum ionization density (Nmax),
geomagnetic activity and the neutral dynamics. There is increasing
evidence in the literature during the recent past that shows a well
developed Equatorial Ionization Anomaly (EIA) during the afternoon hours
contributes significantly to the initiation of ESF during the post-sunset hours.
Also, there exists a good correlation between the Equatorial Ionization
Anomaly (EIA) and the Integrated Equatorial ElectroJet (IEEJ) strength, as
the driving force for both is the same, namely, the zonal electric field at
the equator.
In this paper, we present a linear relationship that exists between the
daytime integrated equatorial electrojet (IEEJ) strength and the maximum
elevated height of the F-layer during post-sunset hours (denoted as peak
h'F). An inverse relationship that exists between the 6-h average
Kp-index prior to the local sunset and the peak h'F of the F-layer is also
presented. A systematic study on the combined effects of the IEEJ and the
average Kp-index on the post-sunset, peak height of the F-layer (peak h'F), which
controls the development of ESF/plasma bubbles, is carried out using the
ionosonde data from an equatorial station, Trivandrum (8.47° N,
76.91° E, dip.lat. 0.5° N), an off-equatorial station, SHAR
(13.6° N, 79.8° E, dip.lat. 10.8° N) and VHF scintillations (244 MHz)
observed over a nearby low-latitude station, Waltair (17.7° N,
83.3° E, dip.lat. 20° N). From this study, it has been found that
the threshold base height of the F-layer at the equator for the development
of plasma bubbles is reduced from 405 km to 317 km as the solar activity
decreases from March 2001 (mean Rz=113.5) to March 2005 (mean Rz=24.5).
This decrease in threshold height with the decreasing solar activity is
explained on the basis of changes in the local linear growth rate of
the collisional Rayleigh-Taylor instability, due to the variability of various
terms such as inverse density gradient scale length (L−1), ion-neutral
collision frequency (νin) and recombination rate (R) with the
changes in the solar activity. |
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