224 research outputs found
Estimating the contribution from different ionospheric regions to the TEC response to the solar flares using data from the international GPS network
This paper proposes a new method for estimating the contribution from
different ionospheric regions to the response of total electron content
variations to the solar flare which uses the effect of partial shadowing of the
atmosphere by the terrestrial globe. The study uses GPS stations located near
the boundary of the shadow on the ground in the nightside hemisphere. The beams
between the satellite-borne transmitter and the receiver on the ground for
these stations pass partially through the atmosphere lying in the region of
total shadow and partially through the illuminated atmosphere. The analysis of
the ionospheric effect of a powerful solar flare of class X5.7/3B that was
recorded on July 14,
2000 (10:24 UT, N22W07) in quiet geomagnetic conditions (Dst=-10 nT) has
shown that about 20% of the TEC increase correspond to the ionospheric region
lying below 100 km, about 5% refer to the ionospheric E-region (100-140 km),
about 30% correspond to the F1-region (140-200 km), and about 30% to regions
lying above 300 km.Comment: LaTeX, 6 pages, 4 figures, 1 tabl
The shock-acoustic waves generated by earthquakes
We investigate the form and dynamics of shock-acoustic waves generated by
earthquakes. We use the method for detecting and locating the sources of
ionospheric impulsive disturbances, based on using data from a global network
of receivers of the GPS navigation system and requiring no a priori information
about the place and time of associated effects. The practical implementation of
the method is illustrated by a case study of earthquake effects in Turkey
(August 17, and November 12, 1999), in Southern Sumatera (June 4, 2000), and
off the coast of Central America (January 13, 2001). It was found that in all
instances the time period of the ionospheric response is 180-390 s, and the
amplitude exceeds by a factor of two as a minimum the standard deviation of
background fluctuations in total electron content in this range of periods
under quiet and moderate geomagnetic conditions. The elevation of the wave
vector varies through a range of 20-44 degree, and the phase velocity
(1100-1300 m/s) approaches the sound velocity at the heights of the ionospheric
F-region maximum. The calculated (by neglecting refraction corrections)
location of the source roughly corresponds to the earthquake epicenter. Our
data are consistent with the present views that shock-acoustic waves are caused
by a piston-like movement of the Earth surface in the zone of an earthquake
epicenter.Comment: EmTeX-386, 30 pages, 4 figures, 3 tabl
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