DSpace Community:
http://hdl.handle.net/2122/94
2014-11-25T04:17:54ZSporadic E layer at mid-latitudes: average properties and influence of atmospheric tides
http://hdl.handle.net/2122/9158
Title: Sporadic E layer at mid-latitudes: average properties and influence of atmospheric tides
Authors: Pignalberi, A.; Dipartimento di Fisica, Università "La Sapienza" di Roma; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: This paper describes a study of the daily variability shown by the main characteristics of the sporadic
E (Es) layer, that is the top frequency (ftEs) and the lowest virtual height (h’Es). The study is based on ionograms recorded by the Advanced Ionospheric Sounder by the Istituto Nazionale di Geofisica e Vulcanologia (AIS-INGV) ionosondes installed in the ionospheric stations at Rome
(41.8° N, 12.5° E) and Gibilmanna (37.9° N, 14.0° E), Italy, during the summer (June, July, August and September) of 2013, a year falling in the ascending phase of solar cycle 24. The ftEs presents a diurnal variation characterized by two maxima, the first around noon is very well defined and the second in the evening/night is much less defined; the amplitude of both maxima decreases from June to September accompanied
by a general decrease of the ftEs values which is more pronounced in the daytime than in the nighttime. h’Es also presents a diurnal variation characterized by two maxima
but, unlike ftEs, these present the same amplitude which is independent from the considered month. Assuming that both ftEs and h’Es trends are influenced by the atmospheric tides, the height–time–intensity (HTI) technique was applied to deeply investigate how these waves control the Es dynamics. The HTI study, along with a fast Fourier transform analysis, show that a well-defined semidiurnal periodicity characterizes the Es layer dynamics most accurately in June and July, while in August and September the daytime semidiurnal
periodicity becomes weaker and the role of the diurnal periodicity is consequently highlighted.2014-11-20T23:00:00ZRay theory formulation and ray tracing method. Application in ionospheric propagation
http://hdl.handle.net/2122/9139
Title: Ray theory formulation and ray tracing method. Application in ionospheric propagation
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Dipartimento di Fisica, Università “Sapienza”, p.le Aldo Moro 2, 00185 Roma, Italia
Abstract: This work will lead to ray theory and ray tracing formulation. To deal with this problem the theory of classical geometrical optics is presented, and applications to ionospheric propagation will be described. This provides useful theoretical basis for scientists involved in research on radio propagation in inhomogeneous anisotropic media, especially in a magneto-plasma. Application in high frequencies (HF) radio propagation, radio communication, over-the-horizon-radar (OTHR) coordinate registration and related homing techniques for direction finding of HF wave, all rely on ray tracing computational algorithm. In this theory the formulation of the canonical, or Hamiltonian, equations related to the ray, which allow calculating the wave direction of propagation in a continuous, inhomogeneous and anisotropic medium with minor gradient, will be dealt. At least six Hamilton’s equations will be written both in Cartesian and spherical coordinates in the simplest way. These will be achieved by introducing the refractive surface index equations and the ray surface equations in an appropriate free-dimensional space. By the combination of these equations even the Fermat’s principle will be derived to give more generality to the formulation of ray theory. It will be shown that the canonical equations are dependent on a constant quantity H and the Cartesian coordinates and components of wave vector along the ray path. These quantities respectively indicated as ri(τ), pi(τ) are dependent on the parameter τ, that must increase monotonically along the path. Effectively, the procedure described above is the ray tracing formulation. In ray tracing computational techniques, the most convenient Hamiltonian describing the medium can be adopted, and the simplest way to choose properly H will be discussed. Finally, a system of equations, which can be numerically solved, is generated.2014-10-22T22:00:00ZA comparative sporadic-E layer study between two mid-latitude ionospheric stations,
http://hdl.handle.net/2122/9106
Title: A comparative sporadic-E layer study between two mid-latitude ionospheric stations,
Authors: Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: Hourly systematic measurements of the highest frequency reflected by the sporadic-E layer (foEs) recorded from January 1976 to June 2009 at the ionospheric stations of Rome (Italy, 41.8 N, 12.5 E) and Gibilmanna (Italy, 37.9 N, 14.0 E) were considered to carry out a comparative study between the sporadic E layer (Es) over Rome and Gibilmanna. Different statistical analysis were performed taking into account foEs observations near the periods of minimum and maximum solar activity. The results reveal that: (1) independently from
the solar activity, Es develops concurrently over extended regions in space, instead of being a spatially limited layer which is transported horizontally by neutral winds over a larger area; especially during summer months, when an Es layer is present at Rome, there is a high probability that an Es layer is also present over Gibilmanna, and vice versa; (2) Es layer lifetimes of 1–5 h were found; in particular, Es layers with lifetimes of 5 h both over Gibilmanna and Rome are observed with highest percentages of occurrence in summer ranging
between 80% and 90%, independently from the solar activity; (3) latitudinal effects on Es layer occurrence emerge mostly for low solar activity during winter, equinoctial, and summer months, when Es layers are detected more frequently over Gibilmanna rather than Rome; (4) when the presence of an Es layer over Rome and Gibilmanna is not simultaneous, Es layer appearance both over Rome and Gibilmanna confirms to be a locally confined event, because drifting phenomena from Rome to Gibilmanna or vice versa have
not been emphasized.2014-07-14T22:00:00ZThe calculation of ionospheric absorption with modern computers
http://hdl.handle.net/2122/9104
Title: The calculation of ionospheric absorption with modern computers
Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: New outcomes are proposed for ionospheric absorption starting from the Appleton-Hartree formula, in its complete form. The range of applicability is discussed for the approximate formulae, which are usually employed in the calculation of non-deviative absorption coefficient. These results were achieved by performing a more refined approximation that is valid under quasi-longitudinal (QL) propagation conditions. The more refined QL approximation and the usually employed non-deviative absorption are compared with that derived from a complete formulation. Their expressions, nothing complicated, can usefully be implemented in a software program running on modern computers. Moreover, the importance of considering Booker’s rule is highlighted. A radio link of ground range D = 1000 km was also simulated using ray tracing for a sample daytime ionosphere. Finally, some estimations of the integrated absorption for the radio link considered are provided for different frequencies.2014-10-14T22:00:00ZShort-term forecasting regional model to predict M(3000)F2 over the European sector: Comparisons with the IRI model during moderate, disturbed, and very disturbed geomagnetic conditions
http://hdl.handle.net/2122/9103
Title: Short-term forecasting regional model to predict M(3000)F2 over the European sector: Comparisons with the IRI model during moderate, disturbed, and very disturbed geomagnetic conditions
Authors: Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The hourly measurements of M(3000)F2 (M(3000)F2meas) and the hourly quiet-time values of M(3000)F2 (M(3000)F2QT) relative to
the ionospheric observatories of Poitiers, Lannion, Dourbes, Slough, Rome, Juliusruh, Kaliningrad, Uppsala, Lyckesele, Sodankyla, and Kiruna as well as the hourly time-weighted accumulation series derived from the geomagnetic planetary index ap (ap(s)), were considered during the period January 1957–December 2003 and used for the development of 11 short-term forecasting local models (STFLM) of M(3000)F2.
Under the assumption that the ionospheric disturbance index ln(M(3000)F2meas/M(3000)F2QT) is correlated to the integrated geomagnetic index ap(s), a set of regression coefficients were established over 12 months and 24 h for each of the 11 observatories under consideration
and used as input to calculate the short-term ionospheric forecasting of M(3000)F2 for three different ranges of geomagnetic activity. The 11 short-term forecasting local models all together constitute a single short-term forecasting regional model (STFRM) of
M(3000)F2. The monthly median predictions of M(3000)F2 provided by the IRI model at the 11 local stations were used to make some comparisons with the predictions of M(3000)F2 carried out by the STFRM.
The results showed that: (1) under moderate geomagnetic activity there are no significantly differences between STFRM and IRI performance because quiet geomagnetic conditions are not so diverse from moderate geomagnetic conditions; (2) under disturbed geomagnetic activity, performances of STFRM significantly better than IRI emerge only in some cases; (3) the STFRM’s performances are
always significantly better than those provided by IRI under very disturbed geomagnetic activity, consequently the operative use of the STFRM could be valuable in providing short-term forecasting maps of M(3000)F2 over the European area during very disturbed geomagnetic conditions.2014-07-14T22:00:00ZComment on “Temporal and spatial precursors in ionospheric total electron content of the 16 October 1999 Mw7.1 Hector Mine earthquake”, by Su et al. (2013)
http://hdl.handle.net/2122/9101
Title: Comment on “Temporal and spatial precursors in ionospheric total electron content of the 16 October 1999 Mw7.1 Hector Mine earthquake”, by Su et al. (2013)
Authors: Masci, F; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Thomas, J. N.; NorthWest Research Associates, Redmond, Washington, USA
Abstract: We review the recent paper by Su et al. [2013]. Using Global Position System (GPS) and Global Ionospheric Maps (GIM) data, Su et al. claimed to have found ionospheric precursors a few days before the 16 October 1999 Hector Mine, California earthquake. They proposed that this type of analysis of ionospheric data may be useful for locating forthcoming large earthquakes. In this Comment, we reexamine these data and show that ionospheric anomalies reported by Su et al. were not precursors to the Hector Mine earthquake. Therefore, their proposed analysis is not useful in the context of earthquake prediction.2014-08-07T22:00:00ZUnusual nighttime impulsive enhancements of electron density characterizing the low-latitude ionosphere: Phenomenology and possible mechanisms of triggering
http://hdl.handle.net/2122/9092
Title: Unusual nighttime impulsive enhancements of electron density characterizing the low-latitude ionosphere: Phenomenology and possible mechanisms of triggering
Authors: Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: Unusual nighttime impulsive electron density enhancements that are rarely observed at low latitudes on a wide region of South America are here investigated. These phenomena are very atypical because besides being of brief
duration, they are characterized by a pronounced compression of the ionosphere.
The events were studied and analyzed using both the F2 layer critical frequency (foF2) and the lowest virtual height of the ordinary trace of the F region (h'F) values
recorded at five ionospheric stations widely distributed in space. A careful analysis
of isoheight ionosonde plots suggests that traveling ionospheric disturbances (TIDs)
caused by atmospheric gravity wave (AGW) propagation could play a significant
role in causing these phenomena, both for quiet and for medium-high geomagnetic
activity; in the latter case however a nocturnal recharging of the fountain effect, due to electric fields penetrating from the magnetosphere, plays an as much significant
role.2014-08-31T22:00:00ZScientific review on the ionospheric absorption and research prospects of a Complex Eikonal model for one-layer ionosphere
http://hdl.handle.net/2122/9071
Title: Scientific review on the ionospheric absorption and research prospects of a Complex Eikonal model for one-layer ionosphere
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ippolito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cesaroni, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: Thepresent paper conducts a scientific review on ionospheric absorption, extrapolating the research prospects of a complex eikonal
model for one-layer ionosphere. As regards the scientific review, here a quasi-longitudinal (QL) approximation for nondeviative
absorption is deduced which is more refined than the corresponding equation reported by Davies (1990). As regards the research
prospects, a complex eikonal model for one-layer ionosphere is analyzed in depth here, already discussed by Settimi et al. (2013). A
simple formula is deduced for a simplified problem. A flat, layered ionospheric medium is considered, without any horizontal
gradient. The authors prove that the QL nondeviative amplitude absorption according to the complex eikonal model is more
accurate than Rawer’s theory (1976) in the range of middle critical frequencies.2014-08-05T22:00:00ZUnusual nighttime impulsive foF2 enhancements at low latitudes: Phenomenology and possible explanations
http://hdl.handle.net/2122/9046
Title: Unusual nighttime impulsive foF2 enhancements at low latitudes: Phenomenology and possible explanations
Authors: Perna, L.; Dipartimento di Fisica, Universita` di Roma “La Sapienza”; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Fagundes, P. R.; Universidade do Vale do Paraı´ba, 12244-000 Sa˜o Jose´ dos Campos, Brazil; de Jesus, R.; Universidade do Vale do Paraı´ba, 12244-000 Sa˜o Jose´ dos Campos, Brazil; Cabrera, M. A.; Laboratorio de Ionosfera, Departamento de Fısica, FACET, Universidad Nacional de Tucumán, 4000 Tucumán, Argentina; Ezquer, R. G.; Laboratorio de Ionosfera, Departamento de Fısica, FACET, Universidad Nacional de Tucumán, 4000 Tucumán, Argentina
Abstract: This paper is focused on unusual nighttime impulsive electron density enhancements that are rarely observed at low latitudes on a
wide region of South America, under quiet and medium/high geomagnetic conditions. The phenomenon under investigation is very peculiar because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. The phenomenon was studied and analyzed using both the F2 layer critical frequency (foF2) and the virtual height of the base of the F region (h'F) values recorded at five ionospheric stations widely distributed in space, namely: Jicamarca (-12.0°, -76.8°, magnetic latitude -2.0°), Peru; Sao Luis (-2.6°, -44.2°, magnetic latitude +6.2°), Cachoeira Paulista (-22.4°, -44.6°, magnetic latitude -13.4°), and Sao Jose´ dos Campos (-23.2°, -45.9°, magnetic latitude -14.1°), Brazil; Tucumán (-26.9°, -65.4°, magnetic latitude -16.8°), Argentina. In a more
restricted region over Tucumán, the phenomenon was also investigated by the total electron content (TEC) maps computed by using measurements from 12 GPS receivers. A detailed analysis of isoheight ionosonde plots suggests that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could play a significant role in causing the phenomenon both for quiet and for medium/high geomagnetic activity; in the latter case however a recharging of the fountain effect, due to electric fields penetrating from the
magnetosphere, joins the TID propagation and plays an as much significant role in causing impulsive electron density enhancements.2014-07-31T22:00:00ZDescription of ionospheric disturbances observed by Vertical Ionospheric Sounding at 3 MHz
http://hdl.handle.net/2122/8978
Title: Description of ionospheric disturbances observed by Vertical Ionospheric Sounding at 3 MHz
Authors: Baskaradas, J. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: High Frequency radio waves reflected by the ionosphere can provide a
relevant amount of information within the composite received signal.
The ionosphere is indeed a frequency dispersive, bi-refractive, absorbing
medium, in which multipath propagation occurs due to disturbance on a
varied time-spatial scale. On the time-spatial level of Small Scale Disturbances
(SSD) the ionosphere dynamics, detectable by Vertical Ionospheric
Sounding (VIS), is mainly dependent on wrinkled layers acting as
multi-reflectors. The present paper discusses different aspects of the effects
of multipath fading suffered by the wave along the propagation path and
potentially associated with SSD. To achieve these objectives, a VIS campaign
at a fixed frequency of 3.0 MHz was conducted at the ionospheric
observatory in Rome (Latitude 41.8 N; Longitude 12.5 E), by collecting a
series of measurements of the power variations in received echo signals
recorded between two consecutive ionograms whose sounding repetition
rate was set to 15 min. The obtained results show that: 1) the fading suffered
by the wave follows either a Rayleigh trend or a Nakagami-Rice trend, or
a mix of them, the mixed case being the most frequent (about 65 % of the
analysed cases); 2) the predominant periodicities characterizing the power
variation are less than 25 s; such values are compatible with the small
scale ionospheric disturbances; 3) for all the 24 hours of the day the ionospheric
reflector is pretty stable and for time intervals of 10-30 s the periods
of stability occur with a percentage of occurrence ranging between 55%
and 95 %; for time intervals of 190- 210 s the periods of stability occur instead
with a percentage of occurrence ranging between 5% and 54 %.2013-12-31T23:00:00Z