[Show abstract][Hide abstract] ABSTRACT: 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.
Advances in Space Research 01/2015; 55(1):243-258. · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ionospheric TEC (Total Electron Content) variations derived from GPS
measurements at 17 stations 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 Jan-21 Apr. 2009. After analyzing
non-interpolated TEC data of 5 GPS stations in Central Italy (Unpg (Perugia),
Untr, Aqui (Aquila), M0se (Roma) and Paca (Palma)), 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 TEC disturbance was
localized at heights below 160 km, i.e. in the lower ionosphere.
[Show abstract][Hide abstract] ABSTRACT: The ISIS project (Inter-Satellite & In Situ plasmaspheric monitoring and modelling) aimed to design a system for the continuous monitoring of the Earth’s plasmasphere based on the future Galileo satellites.
The ISIS Team proposed new experimental facilities on board of future generation Galileo satellites, designed to realize inter-satellite and in situ measurements to monitor global and local quantities; in particular, a scalable system of Langmuir probes was suggested, while the TEC along all possible inter-satellite ray paths throughout the plasmasphere could be monitored via phase- and group-delay analysis of inter-satellite radio signals.
ISC-CNR (Institute for Complex Systemsof the National Research Council of Italy), INGV (Istituto Nazionale di Geofisica e Vulcanologia) and TAS-I (Thales Alenia Space - Italy) were joining forces in this project.
4th International Colloquium Scientific and Fundamental Aspects of the Galileo Programme, Prague; 12/2013
[Show abstract][Hide abstract] ABSTRACT: The problem of ionospheric variability is regarded from the point of view of spatial and temporal correlations between the GPS TEC variations derived from the neighboring GPS receiver records. It is demonstrated that the technique of the spatial correlation coefficient developed earlier to reveal the ionospheric variations induced by seismic activity sometimes is not very reliable. The new index of the local ionospheric variability is proposed describing the spread of GPS TEC within the given area. It is tested for periods of geomagnetic disturbances and periods of several days preceding the strong (M ⩾ 6) earthquakes occuring within the area of GPS receiver’s network. It is shown that the new index is a promising indicator of the earthquake preparation process, it increases few (5–10) days before the seismic shocks and comes back to normal state after the earthquake. During the periods of increased geomagnetic activity the index does not show such variability.
Advances in Space Research 05/2013; · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe the introduction of the first all-sky imaging system for
low-light-level optical observations of the disturbed ionosphere over
mid-latitude Europe. Using 6300 Å auroral emissions that come from
the 200-400 km altitude range, we demonstrate that sub-visual optical
patterns spanning the European continent can be obtained from a single
site in Italy. Pilot observations during the 26-27 September 2011
geomagnetic storm show that the diffuse aurora's low latitude boundary
can be used to find where the poleward wall of the ionospheric trough is
located. This relates directly to regions of radiowave disruptions
caused by the precipitation of energetic particles from the
magnetospheric plasma sheet that move to lower latitudes during space
weather events. Images of stable auroral red (SAR) arcs can be used to
track the magnetospheric ring current and plasmapause location, a second
region of radiowave interference. Comparisons with ground-based and
satellite observations of the ionosphere during the same storm
demonstrate how ASI images reveal the lowest energy components of
magnetospheric input to the ionosphere-thermosphere system. Such
observations can be used, potentially, for both now-casting of storm
effects spanning Europe, and for retrospective validation of existing
models of space weather impacts at sub-auroral locations.
Space Weather 02/2013; 11(2):1-10. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NeQuick 2 ionospheric empirical model depends on global ionospheric
coefficients that are estimated from unevenly distributed ionosonde
measurements. In regions, like Africa, where very few observational data
were available until recently, the model estimated the ionospheric peak
parameters by interpolation. When one wants to employ the model to
specify the ionosphere where very few data have been used for model
development, the performances of the model need careful validation. This
study investigates the performances of NeQuick 2 in the East African
region by assisting the model with measurements from a single Global
Positioning System (GPS) receiver, which has been deployed recently.
This can be done by first calculating an effective ionization level that
drives NeQuick 2 to compute slant total electron content (sTEC) which
fits, in the least square sense, with the measurements taken from a
single GPS receiver. We then quantify the performances of NeQuick 2 in
reproducing the measured TEC by running the model at four other
locations, where GPS stations are available, using the same effective
ionization level that we calculated from a single GPS station as a
driver of the model. Finally, the performances of the model before and
after data ingestion have been investigated by comparing the model
results with the experimental sTEC and vertical TEC (vTEC) obtained from
the four test stations. Three months data during low solar activity
conditions have been used for this study. We have shown that the
capability of NeQuick 2, in describing the East African region of the
ionosphere, can be improved substantially by data ingestion. We found
that the model after ingestion reproduces the experimental TEC better as
far as about 620 km away from the reference station than that before
adaptation. The statistical comparisons of the performances of the model
in reproducing sTEC before and after ingestion are also discussed in
Radio Science 10/2012; 47(5):5002-. · 1.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An unusual nighttime impulsive electron density enhancement was observed on 6 March 2010 over a wide region of South America, below the southern crest of the equatorial anomaly, under low solar activity and quiet geomagnetic conditions. The phenomenon was observed almost simultaneously by the F2 layer critical frequency (foF2) recorded at three ionospheric stations which are widely distributed in space, namely Cachoeira Paulista (22.4°S, 44.6°W, magnetic latitude 13.4°S), São José dos Campos (23.2°S, 45.9°W, magnetic latitude 14.1°S), Brazil, and Tucumán (26.9°S, 65.4°W, magnetic latitude 16.8°S), Argentina. Although in a more restricted region over Tucumán, the phenomenon was also observed by the total electron content (TEC) maps computed by usingmeasurements from 12 GPS receivers. The investigated phenomenon is very particular because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. This compression was clearly visible both by the virtual height of the base of the F region (h′F) recorded at the aforementioned ionospheric stations, and by both the vertical electron density profiles and the slab thickness computed over Tucumán. Consequently, neither an enhanced fountain effect nor plasma diffusion from the plasmasphere can be considered as the single cause of this unusual event. A thorough analysis of isoheight and isofrequency ionosonde plots suggest that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could have likely played a significant role in causing the phenomenon.
Journal of Geophysical Research Atmospheres 12/2011; 116(A12314). · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied six different parameters derived from three different radiophysical techniques used to monitor area over the central Italy around the time of L'Aquila M6.3 earthquake of 6 April 2009. Namely VLF monitoring, ground based ionospheric sounding and GPS vertical TEC. The parameters derived from these data are: variations of amplitude of VLF signal on different propagation passes, critical frequency foF2 variations, cross-correlation coefficient for different pairs of ground based ionosondes, vertical GPS TEC time series, local variability index for the network of GPS receivers, and GPS TEC map. High congruence of techniques in time and space is found.
General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
[Show abstract][Hide abstract] ABSTRACT: It is rather well recognized that the global dynamics of the Sun–Earth relationship involves complex nonlinear phenomena. Here we present a preliminary attempt to characterize the influence and the timing of the solar magnetic activity on the near-Earth environment, based on quite novel tools based on concepts from information theory.In detail, we show two preliminary examples. In the first one, we investigate the time behaviour of the delayed mutual information applied to the solar wind forcing on ionospheric irregularities in a stormy period of November 2004; in the other example, we study the evolution of a possible measure of relative complexity for the diurnal variability of the vertical total electron content during the “Halloween Storm” of year 2003.The future use of data from the Galileo system will give a definitive improvement to the application of such techniques to Space Weather.
Advances in Space Research 03/2011; 47(5):877-885. · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: GPS measurements of total electron content (TEC) variations in Central Italy for the period 01 January-30 April 2009 are exploited in order to examine possible TEC variation signatures associated with the L'Aquila earthquake (EQ) on 6 April 2009. An irregular change of TEC characterizing the L'Aquila's region is initiated on day 095 (05 April 2009). This specific change in TEC starts before noon hours and, with variable amplitude, persists till the EQ shock moment occurred at 01:32:39 UT. A comparison with TEC data of other GPS stations reveals that the duration of this TEC changes maximizes at L'Aquila, its amplitude maximum (in fact, of short duration less than one hour)) however is stretched in southwest direction from L'Aquila at a distance of ~100 km. The spatial extension of this TEC change characterizes distances of 300 km and even more from L'Aquila. TEC changes are compared with ionosonde measurements at Rome and other stations for day 095. Mechanisms of generation of the recorded TEC change are discussed. Analysis of magnetic field variations of localized sources and possible relationships with the observed TEC changes are undertaken.
[Show abstract][Hide abstract] ABSTRACT: Latest studies related to Abruzzo earthquake (Italy) (Fall AGU 2009), have reported precursory signals observed on the ground and in space associated with earthquake of April 6, 2009. Further questions, that are still been debating in the science community are: (1) whether such signals systematically precede most of the earthquakes in the region; and (2) what is the physical link between the earthquake processes and the atmospheric/ ionospheric signals ? To address some of these we present four different data sets of continuous observations for 5 years period (2005-2009) and their temporal and spatial dynamics several days before the Abruzzo earthquake. This earthquake was in the middle point between three radon ground stations. Beginning March 30th, 2009 radon enhancement coincides (with some delay) with an increase in air temperature in the epicentral area. And subsequently from April 1 to 3, 2009 an increase of outgoing infra-red radiation was observed from satellite data. The GPS/Total Electron Content (TEC) data indicate an increase of electron concentration reaching a maximum on April 5, 2009. We have found a significant relationship between radon emanation and atmospheric and ionospheric anomalies associated with Abruzzo earthquake. This study conforms: (1) Our initial findings of atmospheric awakening prior to the Abruzzo earthquake; and (2) Demonstrate the presence of related variations of several parameters implying their connection to the earthquake preparation process. This study also can help to understand different short-term earthquake precursors and their association with earthquakes described by Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model.
Geophysical Research Abstracts. 01/2010; 12(1):12869-12869.
[Show abstract][Hide abstract] ABSTRACT: Recent studies indicate an enhanced coupling between the atmospheric boundary layer and the ionosphere, which have been proposed to be related with large (>M6) earthquakes. We present observations data from January to April 2009 of five physical parameters and their temporal and spatial variations several days before the onset of the Abruzzo earthquake. This earthquake was situated in the middle of three ground stations monitoring radon. These data show an increase prior to the main earthquake beginning on March 30th this enhancement of radon coincides (with some delay) with an increase in the air temperature (measured on the ground) in the epicentral area. And subsequently from April 1 to 3 there was an association with the acceleration of outgoing infra-red radiation observed on the top of the atmosphere from satellite. The GPS/Total Electron Content data indicate an increase of electron concentration in ionosphere from April 3 to 5, reaching a maximum on April 5. We have found a significant relationship between radon emanation and atmospheric and ionospheric anomalies associated with Abruzzo earthquake. This relationship has been studied using an integrated set of observations of several physical and environmental parameters (radon, seismicity, temperature of the atmosphere boundary layer, outgoing earth infra-red radiation and GPS/TEC). Our results suggest for an existence of coupling process between radon activity and atmosphere, several days in advance to the April 6th Abruzzo earthquake.
[Show abstract][Hide abstract] ABSTRACT: The IRI model offers a choice of options for the computation of the electron density profile and electron content (TEC). Recently new options for the topside electron density profile have been developed, which have a strong impact on TEC. Therefore it is important to test massively the IRI and the new options with experimental data. A large number of permanent stations record dual frequency GPS data from which it is possible to obtain TEC values. Thirty-one worldwide distributed stations have been selected to investigate the capabilities of the IRI to reproduce experimental TEC. Data for years 2000 (high solar activity) and 2004 (medium solar activity) have been analyzed computing modeled values with the IRI-2001 and the IRI-2007-NeQuick topside options. It is found that IRI-2007-NeQuick option generally improves the estimate of the slant TEC, especially in the case of high latitudes stations during high solar activity.
Advances in Space Research 08/2008; · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Equatorial plasma bubbles (EPBs) are field-aligned depletions of F-region ionospheric plasma density that grow from irregularities caused by the generalized Rayleigh–Taylor instability mechanism in the postsunset equatorial sector. Although they have been studied for some decades, they continue to be an important subject of both experimental and theoretical investigations because of their effects on trans-ionospheric radio communications.In this work, calibrated data of slant total electron content (sTEC) taken every 10 min from EGNOS System Test Bed Brazzaville (Congo), Douala (Cameroon), Lome (Togo) and N’Djamena (Chad), and International GNSS Service Ascension Island, Malindi (Kenya), and Libreville (Gabon), stations are used to detect plasma bubbles in the African equatorial region during the first 6 months of 2004. To identify these irregularities, the trend of every curve of sTEC against time is subtracted from the original data. The size of the EPBs is estimated by measuring its amplitude in the de-trended time variation of sTEC.
Journal of Atmospheric and Solar-Terrestrial Physics 04/2008; · 1.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present results from our studies of atmospheric and ionospheric electromagnetic (EM) signals preceding major earthquakes. This study examines possible associations relating anomalous changes of thermal and ionospheric parameters observed around the time of several strong earthquakes (M8.0 in Peru and 1999-2005 in California). Our approach requires an integrated analysis of several physical and environmental parameters (thermal infrared electromagnetic fields, latent heat flux, ionospheric parameters, specifically GPS/TEC, DEMETER and electron density, air temperature and humidity of the boundary layer, and seismicity) that have been found to be associated with impending earthquakes. The ionospheric and atmospheric observational methodology we present is based on a joint analysis of: (1) satellite long-wavelength radiation data form NOAA; (2) surface latent heat flux (SLHF); (3) GPS/TEC and DEMETER; and (4) thermal infrared data from (NASA EOS/MODIS) together with ground air temperature and humidity measurements. Our latest understanding from several post-earthquake independent analyses takes into account the problem of proper evaluation of such alarm techniques for upcoming major (M>5.5, depth
[Show abstract][Hide abstract] ABSTRACT: The NeQuick ionospheric electron density model has a very simple topside formulation, which allows taking into account the electron content up to 20,000km. In the present work, the Gallagher model has been used in connection with NeQuick to provide a more realistic representation of the electron concentration distribution in the plasmasphere. An analysis of the impact of the proposed modification in low geomagnetic latitudes (±40°) on modeled vertical total electron content has been performed for different levels of solar activity, season, and universal time.In addition, GPS vertical total electron content values obtained from seven IGS (International GPS Service) station data have been compared with the NeQuick and NeQuick+Gallagher vertical total electron content values, confirming the importance of including a plasmaspheric formulation in the NeQuick model.
Advances in Space Research 01/2007; 39(5):739-743. · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Global Positioning System (GPS) has become a powerful tool for ionospheric studies. In addition, ionospheric corrections
are necessary for the augmentation systems required for Global Navigation Satellite Systems (GNSS) use. Dual-frequency carrier-phase
and code-delay GPS observations are combined to obtain ionospheric observables related to the slant total electron content
(sTEC) along the satellite-receiver line-of-sight (LoS). This observable is affected by inter-frequency biases [IFB; often
called differential code biases (DCB)] due to the transmitting and the receiving hardware. These biases must be estimated
and eliminated from the data in order to calibrate the experimental sTEC obtained from GPS observations. Based on the analysis
of single differences of the ionospheric observations obtained from pairs of co-located dual-frequency GPS receivers, this
research addresses two major issues: (1) assessing the errors translated from the code-delay to the carrier-phase ionospheric
observable by the so-called levelling process, applied to reduce carrier-phase ambiguities from the data; and (2) assessing
the short-term stability of receiver IFB. The conclusions achieved are: (1) the levelled carrier-phase ionospheric observable
is affected by a systematic error, produced by code-delay multi-path through the levelling procedure; and (2) receiver IFB
may experience significant changes during 1day. The magnitude of both effects depends on the receiver/antenna configuration.
Levelling errors found in this research vary from 1.4 total electron content units (TECU) to 5.3 TECU. In addition, intra-day
vaiations of code-delay receiver IFB ranging from 1.4 to 8.8TECU were detected.
Journal of Geodesy 01/2007; 81(2):111-120. · 3.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work describes results from our analysis of: (1) GPS Total Electron
Content (TEC) measurements collected from ground based stations; (2)
ionospheric electromagnetic plasma measurements from the DEMETER
satellite; (3) thermal infrared (TIR) data (NOAA/AVHRR, MODIS); (4)
emitted long-wavelength radiation (OLR) and; (5) surface latent heat
flux (SLHF) from NOAA/NCEP. We found atmospheric and ionospheric
anomalies approximately one week prior for both the Dec 26, 2004, M 9.0
Sumatra-Andaman Islands and the March 28, 2005, M 8.7 Northern Sumatra
earthquakes. There were 125 earthquakes (M>5.5) in the 118 days of
data (December 1, 2004 through April 1, 2005) we analyzed in this region
(0°-10°, N and 90°-100° E). Ionospheric variations
(GPS/TEC), associated with the Northern Sumatra events, were determined
from data of both the regional SuGAr array (13 stations in Indonesia)
and four IGS stations. For each station a time series of the vertical
TEC (VTEC) data were computed and compared with the magnetic Dst index,
to see if these signals were the result of external magnetic field
activity. On December 22, four days prior to the M9.0 quake, GPS/TEC
data reached a monthly maximum with low Dst values. For the M 8.7 March
28 earthquake values of GPS/TEC were observed to increase four days
(March 22-25) prior to the event again with low Dst values. The VLF/ICE
instrument on DEMETER was operational during the M 8.7 earthquake of
March 28, 2005. Our analysis shows intensive ELF emissions within the 0
-200 Hz window at the conjugated points on 22 of March, 2005, 6 days
before the earthquake during DEMETERs close proximity to the epicenter.
In the case of the Dec 26, 2004, M 9.0 quake, OLR data were >80 W/m2,
corresponding to approximately two sigma above the mean for the months
of December, between 2001 and 2004, were found on December 21, 2004,
five days before the event. Anomalous values of SLHF associated with the
M9.0 Sumatra-Andaman Islands earthquake event were found on Dec 7, 2005
(above five sigma) and Dec 22, 2005 (SLHF +280Wm2). Smaller anomalies
are also seen on Mar 23, 2005 (SLHF +180Wm2). The anomalies consistently
occur over regions of maximum stress (along continental boundaries), and
appear not to be atmospheric due to the long persistence over the same
[Show abstract][Hide abstract] ABSTRACT: We analyzed different and independent data sources - GPS Total Electron Content (TEC) collected from ground based (GPS) and satellite TIR (thermal infrared) data (NOAA/AVHRR) emitted long-wavelength radiation (OLR) and surface latent heat flux (SLHF- from NOAA/NCEP) prior to and during M7.6 Kashmir earthquake of October 8, 2005. Ionospheric variations (GPS/TEC) associated with this event were determined by regional GPS station located in Bhopal (23.2°N, 77.4°E and magnetic inclination 18.5°N). A two- month long time series of the vertical TEC (VTEC) data were compiled together with the disturbance storm- time (Dst) indices. An anomalous value of SLHF associated with the October 8 earthquake was observed starting on October 1 one week prior to the event over the greater area of the epicenter. Strong anomalous SLHF values have been detected for several coastal earthquakes before, but this was the first time we observed SHLF anomaly for an intraplate earthquake hundreds of km away from the coast. Recent analysis of the continuous OLR from the Earth surface indicates anomalous variations (on top of the atmosphere) prior to a number of medium to large earthquakes. In the case of the Kashmir earthquake, compared to the reference fields for the months of December between 2001 and 2004, we found OLR anomalous fluxes, of the order of >72 W/m2, with an absolute value of 282 W/m2 along the epicentral area beginning October 6, two days before the event. Ground thermal measurement indicated similarity for the monthly minimum of relative humidity (30%) and monthly maximum of daily air temperate on October 6, 2005. Our initial results need additional validation and they could be explained within the framework of a model of Lithosphere-Atmosphere- Ionosphere coupling between the crust and the atmosphere/ionosphere. This methodology has a great potential to increase the scientific understanding of earthquake preparation processes and could be used for a future Global Earth Observation System for Natural Hazards.