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stronger than the observed ones by magnitude in the model case. (3) The increased
TEC area occupies a smaller region in the model case. (4) The isoline patterns and
the magnitudes differ from the observed ones but not drastically. The discrepancies
between the simulation results and the GPS observations could be caused by the
rather simplified assumptions about the external electric field sources, their density
distribution, and acting regime.
Night domination effects, the existence of a “ban-time,” and the terminator-
driven TEC anomaly suppression should be caused by the changes of the conduc-
tivity of the ionosphere. It is related to the crossing of the sunrise terminator, where
the well-conducting sunlit ionosphere leads to a depression of the electric potential
disturbances and to a reduction of the electric field, generated by the externally
driven electric current.
4.3.5.3
Case Study of the TEC Disturbances Before the Earthquakes of
1 January 2011, Argentina, M7.0, and 2 January 2011, Chile, M7.1
We considered the earthquakes of 1 January 2011, 09:56 UT/06:56 LT, Argentina,
M7.0 (26.794
ı
S, 63.079
ı
W), D 576.8 km, and 2 January 2011, 20:20 UT/17:20 LT,
Chile, M7.1 (38.354
ı
S, 73.275
ı
W), D 25.1 km as one single (or united) case. The
Chile earthquake took place 1 day after the Argentina earthquake. The positions of
the epicenters are close to each other and can be considered as situated within one
and the same 'traditional' seismic phenomena manifestation area. Therefore, relying
on the traditional pre-earthquake TEC modification signature (spatial and temporal
features), it is impossible to distinguish separately each of the different sources that
impact the ionospheric TEC. On the one hand, the depth of the Argentina earthquake
epicenter was 576.8 km whereas the traditional TEC signatures are statistically
defined only for earthquakes with less than 80-150 km depth; that is, ionospheric
manifestations of such phenomena have not been investigated at all up to now.
On the other hand, the TEC disturbances triggered by this earthquake should, if
ever there are any, be masked or merged with Chile's earthquake effects. The TEC
difference maps for 30.12.2010-02.01.2011 are presented in Fig.
4.20
.
The geomagnetic situation was quiet to moderate for the considered period.
During 22 December 2010-3 January 2011 (except 28-30 December 2010), the
K
p
index was less than 3,
A
p
mostly about 5 nT, and
D
st
was primarily in the range
between
20 nT and
C
10 nT. A moderate magnetic storm occurred during 28-
30 December 2010: on 28 December, the
K
p
index reached values to 4,
A
p
to 27
nT, and the
D
st
index changed from
C
13 nT at 10 UT down to
43 nT at 17
UT on 28 December 2010. As the moderate magnetic storm generated, in 28-30
December 2010, TEC disturbances of considerable magnitude that are able to mask
the seismo-related variations, we excluded the TEC difference maps of this period
from the analysis. Therefore, the considered long-living TEC disturbances linked
to the near-epicenter position were expected to be caused by going through the
underlying atmosphere impact.
In the case of the earthquakes of 1 January 2011, Argentina, M7.0 and 2 January
2011, Chile, M7.1, significant TEC enhancements took place 1 January 2011,
