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| Titel |
Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers |
| VerfasserIn |
O. P. Verkhoglyadova, B. T. Tsurutani, A. J. Mannucci, M. G. Mlynczak, L. A. Hunt, T. Runge |
| 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 ; 31, no. 2 ; Nr. 31, no. 2 (2013-02-19), S.263-276 |
| Datensatznummer |
250017755
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| Publikation (Nr.) |
 copernicus.org/angeo-31-263-2013.pdf |
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| Zusammenfassung |
We study solar wind–ionosphere coupling through the late declining
phase/solar minimum and geomagnetic minimum phases during the last solar
cycle (SC23) – 2008 and 2009. This interval was characterized by sequences
of high-speed solar wind streams (HSSs). The concomitant geomagnetic
response was moderate geomagnetic storms and high-intensity, long-duration
continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map
(GIM) software and the GPS total electron content (TEC) database were used
to calculate the vertical TEC (VTEC) and estimate daily averaged values in
separate latitude and local time ranges. Our results show distinct low- and
mid-latitude VTEC responses to HSSs during this interval, with the
low-latitude daytime daily averaged values increasing by up to 33 TECU
(annual average of ~20 TECU) near local noon (12:00 to 14:00 LT)
in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval,
the response to HSSs was a maximum of ~30 TECU increases with a slightly
lower average value than in 2008. There was a weak nighttime ionospheric
response to the HSSs. A well-studied solar cycle declining phase interval,
10–22 October 2003, was analyzed for comparative purposes, with daytime
low-latitude VTEC peak values of up to ~58 TECU (event
average of ~55 TECU). The ionospheric VTEC changes during
2008–2009 were similar but ~60% less intense on average.
There is an evidence of correlations of filtered daily averaged VTEC data
with Ap index and solar wind speed.
We use the infrared NO and CO2 emission data obtained with SABER on
TIMED as a proxy for the radiation balance of the thermosphere. It is shown
that infrared emissions increase during HSS events possibly due to increased
energy input into the auroral region associated with HILDCAAs. The 2008–2009
HSS intervals were ~85% less intense than the 2003 early
declining phase event, with annual averages of daily infrared NO emission
power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and
2009, respectively. The roles of disturbance dynamos caused by high-latitude
winds (due to particle precipitation and Joule heating in the auroral zones)
and of prompt penetrating electric fields (PPEFs) in the solar
wind–ionosphere coupling during these intervals are discussed. A
correlation between geoeffective interplanetary electric field components
and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms
could play important roles in solar wind–ionosphere coupling during
prolonged (up to days) external driving within HILDCAA intervals. |
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