Geoscience Reference
In-Depth Information
To build model difference maps (of the electric potential, zonal, and meridional
electric field and TEC) we first performed a regular calculation without any
additional electric current sources (set as lower boundary condition) to use the
results as quiet background values. Then, an external electric current flowing
between the lower atmosphere and the ionosphere over the Haiti earthquake
(12 January 2010, 21:53 UT, M7.0) epicenter area was used as model input for the
calculations of the ionospheric electric field and the corresponding TEC variations.
Several spatial configurations and magnitudes of these currents have been taken into
consideration: (1) “point” current (equivalent to one cell) sources of different signs
and magnitudes, given in a single node of the numerical grid and (2) “line” sources.
According to UAM simulations, point current sources with magnitudes of about
10 5 and 10 6 A/m 2 given in a single grid node (corresponding to one grid cell
of 5 2 or approximately 500 km 200 km, and averaged vertical electric current
densities of 5 10 6 A/m 2 and 5 10 7 A/m 2 , respectively) induced extremely
strong and unrealistic TEC disturbances and very intense vertical drift motions.
Point sources of 10 9
A/m 2
and 5 10 9
A/m 2
triggered TEC disturbances not
exceeding 15% in magnitude.
The “line” kind sources have been simulated as vertical external currents with a
magnitude of 4 10 8 A/m 2 directed from the ionosphere to the Earth set centric
at nine numerical grid nodes with 5 ı longitudinal steps along the magnetic parallel
of the earthquake epicenter. It corresponds to an external electric current density of
2 10 8 A/m 2 set on the region of approximately 200 km 4,000 km (2 ı along
the meridian and 40 ı along the parallel). The generated TEC disturbances have
reached 20-50% by magnitude depending on the current's spatial distribution
and lifetime. Simulation results are presented in Figs. 4.17 and 4.18 .
As one can see, the additional electric potential generated by the external current
reduces down to zero when approaching the terminator in both (the modelled
and the observed) cases. Corresponding TEC disturbances disappear later than the
electric potential with a time lag of about 4-6 h. The simulations underestimate the
observed magnitude of anomalous TEC increase in the Northern Hemisphere and
overestimate it in the Southern Hemisphere. Both (modeled and observed) cases
show stronger TEC magnitudes at the magnetically conjugated region in comparison
with the near-earthquake epicenter area.
The calculated latitude-altitude variations of the electron density for 08 UT on 11
January 2010 along the -20 ı ,0 ı ,and C 20 ı longitudes are presented in Fig. 4.19 .
As follows from this, the effects in comparison to nondisturbed conditions (i.e.,
without seismic electric current sources) are an electron density 'trough' filling
at the geomagnetic equator and formation of inhomogeneities. At -20 ı longitude,
a mid-latitude maximum stratification took place with a trough formation in the
latitude range of 30-40 ı ;at C 20 ı longitude we see an electron concentration
increase at 300-km height and a depletion of the magnetic tubes higher up. Main
changes took place at the 200-600 km altitude range.
Summarizing the numerical simulation results with external electric currents
flowing between the lower atmosphere and ionosphere caused by seismo-induced
conductivity changes of the underlying atmosphere column, one can state that they
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