[Show abstract][Hide abstract] ABSTRACT: At the 10th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Moscow in 2014 the achievements from the start of TIGER in 1998 were summarized. During that period, great progress was made in measuring, understanding, and modeling the highly variable UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects on the upper atmosphere. However, after more than 50 years of work the radiometric accuracy of SSI observation is still an issue and requires further improvement. Based on the extreme ultraviolet (EUV) data from the SOLAR/SolACES, and SDO/EVE instruments, we present a combined data set for the spectral range from 16.5 to 105.5 nm covering a period of 3.5 years from 2011 through mid of 2014. This data set is used in ionospheric modeling of the global Total Electron Content (TEC), and in validating EUV SSI modeling. For further investigations the period of 3.5 years is being extended to about 12 years by including data from SOHO/SEM and TIMED/SEE instruments. Similarly, UV data are used in modeling activities. After summarizing the results, concepts are proposed for future real-time SSI measurements with in-flight calibration as experienced with the ISS SOLAR payload, for the development of a space weather camera for observing and investigating space weather phenomena in real-time, and for providing data sets for SSI and climate modeling. Other planned topics are the investigation of the relationship between solar EUV/UV and visible/near-infrared emissions, the impact of X-rays on the upper atmosphere, the development of solar EUV/UV indices for different applications, and establishing a shared TIGER data system for EUV/UV SSI data distribution and real-time streaming, also taking into account the achievements of the FP7 SOLID (First European SOLar Irradiance Data Exploitation) project. For further progress it is imperative that coordinating activities in this special field of solar-terrestrial relations and solar physics is emphasized.
Advances in Space Research 08/2015; 56(8). DOI:10.1016/j.asr.2015.07.043 · 1.36 Impact Factor
[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. DOI:10.1016/j.asr.2014.09.029 · 1.36 Impact Factor
[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.
[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; DOI:10.1016/j.asr.2006.04.032 · 1.36 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. DOI:10.1002/swe.20027 · 2.15 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-. DOI:10.1029/2012RS004981 · 1.44 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). DOI:10.1029/2011JA016593 · 3.43 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. DOI:10.1016/j.asr.2010.10.026 · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The outstanding problem faced by operational Global Navigation Satellite
Systems (GNSS) is that ionospheric weather variability is significantly
amplified during disturbed solar maximum conditions. An appropriate
study of the geomagnetic storm-driven ionospheric density disturbances
development is required to estimate the possible impact that storms have
on corrections for GNSS performance improvement. In this paper the
ionospheric response to the major geomagnetic storm (Dst ≤ -250 nT)
during 4 years (2000-2003) of observations at high solar activity in
23th cycle is investigated using ground-based Global Positioning System
(GPS) total electron content (TEC) at Nicosia. We examined the TEC
patterns of storm-time disturbances as measured by the departure from
the average behavior and established consistent features of TEC changes
during ionospheric storms of these magnitudes at the low mid-latitude
location considered in the study. They demonstrate clearly defined
ionospheric space weather effect on communications over the range of
[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.
[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: Several years of hourly daily GPS measurements of the vertical total electron content (TEC) and of the equivalent slab thickness made at different European locations are analysed by using the linear regression technique to demonstrate the response of these two ionospheric parameters to seasonal variations. It is found that both TEC and slab thickness are highly correlated with season. Analytical relationships are determined expressing the seasonal dependence of the vertical TEC and of the equivalent slab thickness as a function of the seasonal parameter cos χ at noon in each location.
Advances in Space Research 09/2009; 44(6):715–724. DOI:10.1016/j.asr.2008.10.036 · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The paper presents results obtained by analyzing high-resolution ionospheric vertical total electron content (vTEC) data set evaluated from a chain of European ground-based Global Positioning System (GPS) stations and its equivalent slab
thickness, as well as the F2-layer critical frequency foF2 and propagation factor M(3000)F2 from nearby ionosonde stations over the period 2006–2007. The study covers data within an area between 36°N and 68°N
geographic latitude, and 7°W and 21°E geographic longitude during these last two years of minimum solar activity in the 23rd
solar cycle. It reveals 15 extraordinary events, all of which exhibited some form of large short-lived vTEC and foF2 enhancements of the duration of small-magnitude solar-terrestrial events. The results clearly show a well-defined vTEC and foF2 storm-like disturbance patterns developed under these conditions. They prove that there are still some open questions related
to the large electron density variations during weak disturbances that require additional study for both their relevance to
different Global Navigation Satellite Systems (GNSS) applications and their role in the formation and evolution of the daytime
ionosphere at middle latitudes.
[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; 42(4-42):770-775. DOI:10.1016/j.asr.2007.09.002 · 1.36 Impact Factor