Geoscience Reference
In-Depth Information
epicenter area. (2) The typical zone of the anomaly maximum manifestation extends
more than 1,500 km in latitude and 3,500-4,000 km in longitude. (3) Anomaly
living time is from several hours or days to couple of weeks before the earthquake
release moment. (4) Analogous effects at the magnetically conjugated area are
often reported. (5) In the case of strong low-latitudinal earthquakes, there are
effects related to the modification of the ionospheric F2-region equatorial anomaly.
From the analysis of the TEC deviations before a few strong recent seismic events
(12 January 2010, Haiti; 1 and 2 January 2011, Argentina and Chile; 11 March
2011, Japan), these pre-earthquake TEC signatures are extended with terminator
and 'ban'-time effects. We strongly believe that the main reason for the appearance
of these TEC anomalies is the vertical drift of F2-region ionospheric plasma under
the influence of a zonal electric field of seismic origin. Increase of the atmospheric
radioactivity level during earthquake preparation leads to enlargement of the ioniza-
tion and electric conductivity of the near-ground atmosphere. Another (and possibly
more effective) ionization mechanism proposed is the so-called positive holes effect.
Changes of resistance of the underlying atmosphere lead to the generation of an ex-
ternal electric current flowing between the Earth and the ionosphere and to the corre-
sponding disturbances of the ionospheric electric field and TEC. These disturbances
were modeled by UAM and compared with the GPS TEC observations. Comparison
shows satisfactory agreement between the model and observations. Methodical
recommendations for detection of ionospheric earthquake precursors are given.
Keywords
High-latitude ionospheric convection Thermospheric neutral wind
Magnetosphere-ionosphere-thermosphere (MIT) coupling Upper Atmosphere
Model (UAM) Solar wind and IMF influence Ionospheric currents
Global total electron content (TEC) pattern Seismogenic ionospheric effects
Earthquake precursors
4.1
Introduction
The weather, climate, and space weather (processes related to solar and geomagnetic
activity) and their forecasting are extremely important for mankind. Observations
and mathematical modeling used together are the modern ways for solving the
forecasting needs. Modern first-principle numerical models are time dependent,
three dimensional (3D), and global. Until recent years these models were being de-
veloped for the lower atmosphere (responsible for the weather and climate; heights
<100 km) and upper atmosphere (responsible for space weather; heights >100 km)
separately, despite the lack of any boundary between these two atmospheric regions.
Their principal physical difference consists of the amount of the charged particles,
the ions and electrons, that is, in their concentration (number density), which is
high in the upper atmosphere and low in the lower. Therefore, electrodynamic
processes are very important in the upper atmosphere (thermosphere, ionosphere,
and magnetosphere).
