Geoscience Reference
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The passages of the sunrise terminator and later of the subsolar point degraded
the anomaly and led to its full decay in the course of the whole day of 9 March,
that is, no significant TEC disturbances were observed on the day of the M7.2
earthquake 9 March, 02:45 UT (which happened at nearly the same exact positions
as the earthquakes of M9, 11 March and the M6.5, 6.022
ı
S, 149.659
ı
E, 21:24 UT).
The equatorial anomaly modifications described above are expected to be the TEC
response on this equatorial earthquake. We also see some moving positive structures
on 10 March, but they are likely caused by activity-driven disturbances.
All the features revealed for the clear case of the Haiti 2010 earthquake were
also shown for both the activity-disturbed (Chile and Argentina, 2011) and multiple-
earthquake (Japan, 11 March 2011) periods. Those features comprise the terminator
and subsolar point-related effects: anomaly depression and 'ban' time at the near-
noon hours, and modification of the shapes of the anomalies under influence of the
terminator approach. In case of the Japan “cluster” earthquakes, the afore-described
features also happened, and the conjugated action of equatorial and mid-latitudinal
earthquakes could be extracted or unambiguously separated. The equatorial one
makes the main impact in Appleton's anomaly modification. Unfortunately, basing
only on the spatial or time interval criteria, it is impossible to distinguish the 9 March
from the M9.0, 11 March, Japan earthquakes. Also, it should be mentioned that the
magnitude of the TEC anomaly is larger than in Haiti (M7.0) or Chile (M7.1) and
Argentina (M7.0) cases. We expect this is the result of the stronger magnitude of the
11 March Japan (M9) earthquake. The warning criteria in this case are applicable
only for region- or country-wide areas, but not for smaller ones. We expect that
'traditional' signatures should be extended with the terminator and subsolar point
related effects.
Sequential consideration of quiet-to-moderate cases showed that solar and
geomagnetic activities can create similar TEC disturbances, but they are not linked
to a fixed geoposition. Their lifetime corresponds to the duration of the activity
disturbances (characterized by the indices of
D
st
,
K
p
, etc.) with some time lag from
the inertness of the ionosphere. They usually originate from the aurora zone and may
penetrate down to middle latitudes. Therefore, the applied technique for the TEC
disturbance discrimination should be very carefully used at high latitudes (>60
ı
),
especially during moderate-to-strong disturbance conditions.
There were no statistical investigations of TEC anomalies related to the deep
earthquakes, so that no precursory schemes exist. Nevertheless, the widely accepted
spatial scale of TEC precursors did not allow us to separate both (Chile and
Argentina) earthquakes from each other. Such combined action, if any, may be
expressed as some shift of the anomalously enhanced region.
4.4
Discussion and Conclusions
We have considered some recent results concerning the modeling of ionospheric
electric fields and their effects on thermospheric dynamics and total electron content
(TEC) variations. The global numerical model of the Earth's upper atmosphere
