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Case Study Results of 28 October 2003 Compared
with CHAMP Data
One of the most intense activity periods in recent history occurred during the
past 23rd solar cycle with a series of extreme solar eruptive events in October-
November 2003 that had serious consequences felt in the entire heliosphere, in
particular throughout the geospheres. These events have already been analyzed
thoroughly in numerous studies; the American Geophysical Union (AGU) Journals
of Geophysical Research Letters (Vol. 32, Nos. 3 and 12, 2005) and the Journal
of Geophysical Research ( Space Physics , Vol. 110, No. A9, 2005) have devoted
special issues to these particular space weather events entitled “Violent Sun-Earth
Connection Events of October-November 2003.” Some of these publications have
direct relevance to key points of the present study (for instance, see Lin et al.
2005 ;LiuandLuhr 2005 ; Sutton et al. 2005 ; Thuillier et al. 2005 ; Tsurutani et al.
2005 ).
On 28 October 2003, 11 UT, an extreme solar flare with significant increases
in EUV and X-ray flux caused increased photo-ionization effects in the dayside
ionosphere and determined a remarkable solar flare effect (SFE) manifestation that
preceded the Halloween superstorm. Some evidence was found for a highly confined
counter electrojet in the dawn sector. Additionally, there are elements, at higher
latitudes, that might suggest in these regions a more significant role of the X-ray
flux and the onset of additional currents below the normal dynamo current region
(Villante and Regi 2008 ).
Figure 4.7 shows the variation of the solar wind IMF B y and B z components
together with some geomagnetic indices ( K p ,AE, D st ) on October 28, 2003, the
day preceding the Halloween superstorm of end October 2003. This particular
day we have chosen as a case study period for a closer inspection of model-
observation comparisons during several CHAMP satellite overflights of the northern
and southern polar regions. The day is characterized by strong changes of IMF
orientation and magnitude. The first half of the day is dominated by conditions of
negative IMF B y with a step-like change between two magnitude levels of this IMF
component: 5 nT until 03:00 UT and 15 nT until 09:30 UT. The IMF
B z component is mostly near zero or negative during this time, and positive during
the subsequent hours until 14:00 UT. Later on, both IMF components are highly
variable throughout the remaining hours of the day.
Liu et al. ( 2007 ) reexamined the 28 October event and showed that neutral and
plasma perturbations during the first phase of the disturbance period contrasted each
other remarkably. They found a decoupling of the neutral and plasma disturbances
during this stage. About 2-3 h after the burst, plasma-neutral coupling via ion
drag was found to become important at low- to mid-latitudes. They concluded that
electrodynamics related to the equatorial fountain dominated the photochemistry in
controlling the plasma density disturbances.
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