33 research outputs found
Intensive MHD-structures penetration in the middle atmosphere initiated in the ionospheric cusp under quiet geomagnetic conditions
In connection with the recently detected quasiperiodical magnetic disturbances in the ionospheric cusp, the penetration of compressional surface magnetohydrodynamic (MHD) waves through the middle atmosphere is modelled numerically. For the COSPAR International Reference Atmosphere (CIRA) 72 model the respective energy density flux of the disturbances in the middle atmosphere is determined. On the basis of the developed model certain conclusions are reached about the height distribution of the structures (energy losses, currents, etc.) initiated by intensive magnetic cusp disturbances
Ionospheric transients observed at mid-latitudes prior to earthquake activity in Central Italy
Ionograms from Rome (41.8N, 12.5E) and Sofia
(42.4N, 23.2E) ionospheric stations during earthquake(EQ)activity with magnitude(M)between 5 and 6 in Central Italy
are analyzed. It is found that several ionospheric disturbances occur in the intermediate E-F region before the EQ
shock. In fact, besides sporadic E (Es) layer development(of type h) of short duration (transients), fmin increase, trace
gaps near the critical frequencies, and E region trace disappearance are also observed within one to three hours before the EQ shock. Before the EQ shocks we find that the F2 region parameters are practically undisturbed. The only exception is the so-called fork trace that appears mostly near the critical frequency of the F2 region. Acoustic gravity waves (AGW) are suggested as one of the possible sources of transients observed in the ionosphere before the EQ shock
Local changes in the total electron content immediately before the 2009 Abruzzo earthquake
Ionospheric TEC (total electron content) variations derived from GPS measurements recorded at 7 GPS stations in Northern, Central and Southern Italy before and after the 2009 Abruzzo earthquake (EQ) of magnitude Mw6.3 were processed and analyzed. The analysis included interpolated and non-interpolated TEC data. Variations in the TEC of both regional and local characteristics were revealed.
Several regional changes were observed in the studied period: 1 January–21 April 2009. After analyzing non-interpolated TEC data
of 5 GPS stations in Central Italy (Unpg (Perugia), Untr (Terni), Aqui (Aquila), M0se (Rome) and Paca (Palma Campania, (Naples)),
a local disturbance of TEC was also found. This local TEC disturbance arises preparatory to the EQ main shock occurred at 01:32 UT on 06 April 2009, maximizes its amplitude of ~0.8 TECu after the shock moment and disappears after it. The local TEC disturbance was confined at heights below 160 km, i.e. in the lower ionosphere
Multi-point ground-based ULF magnetic field observations in Europe during seismic active periods in 2004 and 2005
We present the results of ground-based Ultra Low Frequency (ULF) magnetic field measurements observed from June to August 2004 during the Bovec earthquake on 12 July 2004. Further we give information about the seismic activity in the local observatory region for an extended time span 2004 and 2005. ULF magnetic field data are provided by the South European Geomagnetic Array (SEGMA) where the experience and heritage from the CHInese MAGnetometer (CHIMAG) fluxgate magnetometer comes to application. The intensities of the horizontal <I>H</I> and vertical <I>Z</I> magnetic field and the polarization ratio <I>R</I> of the vertical and horizontal magnetic field intensity are analyzed taking into consideration three SEGMA observatories located at different close distances and directions from the earthquake epicenter. We observed a significant increase of high polarization ratios during strong seismic activity at the observatory nearest to the Bovec earthquake epicenter. Apart from indirect ionospheric effects electromagnetic noise could be emitted in the lithosphere due to tectonic effects in the earthquake focus region causing anomalies of the vertical magnetic field intensity. Assuming that the measured vertical magnetic field intensities are of lithospheric origin, we roughly estimate the amplitude of electromagnetic noise in the Earths crust considering an average electrical conductivity of &lt;&sigma;&gt;=10<sup>&minus;3</sup> S/m and a certain distance of the observatory to the earthquake epicenter
The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements
Several investigations reported the possible identification of anomalous geomagnetic field signals prior to earthquake occurrence. In the ULF frequency range, candidates for precursory signatures have been proposed in the increase in the noise background and polarization parameter (i.e. the ratio between the amplitude/power of the vertical component and that one of the horizontal component), in the changing characteristics of the slope of the power spectrum and fractal dimension, in the possible occurrence of short duration pulses. We conducted, with conventional techniques of data processing, a preliminary analysis of the magnetic field observations performed at L'Aquila during three months preceding the 6 April 2009 earthquake, focusing attention on the possible occurrence of features similar to those identified in previous events. Within the limits of this analysis, we do not find compelling evidence for any of the features which have been proposed as earthquake precursors: indeed, most of aspects of our observations (which, in some cases, appear consistent with previous findings) might be interpreted in terms of the general magnetospheric conditions and/or of different sources
ULF fluctuations of the geomagnetic field and ionospheric sounding measurements at low latitudes during the first CAWSES campaign
We present an analysis of ULF geomagnetic field
fluctuations at low latitudes during the first CAWSES campaign
(29 March–3 April 2004). During the whole campaign,
mainly in the prenoon sector, a moderate Pc3-4 pulsation activity
is observed, clearly related to interplanetary upstream
waves. On 3 April, in correspondence to the Earth’s arrival of
a coronal mass ejection, two SIs are observed whose waveforms
are indicative of a contribution of the high-latitude
ionospheric currents to the low-latitude ground field. During
the following geomagnetic storm, low frequency (Pc5) waves
are observed at discrete frequencies. Their correspondence
with the same frequencies detected in the radial components
of the interplanetary magnetic field and solar wind speed suggests
that Alfv´enic solar wind fluctuations may act as direct
drivers of magnetospheric fluctuations. A cross-phase
analysis, using different pairs of stations, is also presented
for identifying field line resonant frequencies and monitoring
changes in plasmaspheric mass density. Lastly, an analysis
of ionospheric vertical soundings, measured at the Rome
ionosonde station (41.8 N, 12.5 E), and vertical TEC measurements
deduced from GPS signals within an European
network shows the relation between the ULF resonances in
the inner magnetosphere and thermal plasma density variations
during geomagnetically quiet conditions, in contrast to
various storm phases at the end of the CAWSES campaign
The 6 April 2009 earthquake at L’Aquila: a preliminary analysis of magnetic field measurements
Several investigations reported the possible identification
of anomalous geomagnetic field signals prior to
earthquake occurrence. In the ULF frequency range, candidates
for precursory signatures have been proposed in the
increase in the noise background and polarization parameter
(i.e. the ratio between the amplitude/power of the vertical
component and that one of the horizontal component), in the
changing characteristics of the slope of the power spectrum
and fractal dimension, in the possible occurrence of short duration
pulses. We conducted, with conventional techniques
of data processing, a preliminary analysis of the magnetic
field observations performed at L’Aquila during three months
preceding the 6 April 2009 earthquake, focusing attention on
the possible occurrence of features similar to those identified
in previous events. Within the limits of this analysis, we do
not find compelling evidence for any of the features which
have been proposed as earthquake precursors: indeed, most
of aspects of our observations (which, in some cases, appear
consistent with previous findings) might be interpreted
in terms of the general magnetospheric conditions and/or of
different sources
Multi-point ground-based ULF magnetic field observations in Europe during seismic active periods in 2004 and 2005
International audience(Civ. 2e, 17 mars 2016, n° 14-24.986, D. 2016. 700