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http://hdl.handle.net/2122/94
2015-04-01T13:11:37ZOn the onset of ionospheric precursors 40 min before strong earthquakes
http://hdl.handle.net/2122/9429
Title: On the onset of ionospheric precursors 40 min before strong earthquakes
Authors: Masci, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Thomas, J. N.; NorthWest Research Associates, Redmond, Washington, USA.; Villani, Fabio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Secan, J. A.; NorthWest Research Associates, Redmond, Washington, USA.; Rivera, N.; DigiPen Institute of Technology, Redmond, Washington, USA.
Abstract: Heki (2011) and Heki and Enomoto (2013) claimed that anomalous, yet similar, increases of
ionospheric total electron content (TEC) started ~40 min prior to the 2011 Tohoku-Oki, as well as before
other Mw>8 earthquakes. The authors concluded that the reported TEC anomalies were likely related to the
pending earthquakes, suggesting also that TEC monitoring may be useful for future earthquake prediction.
Here we carefully examine the findings of Heki (2011) and Heki and Enomoto (2013) by performing new
analyses of the same TEC data. Our interpretation is that the 40 min onset of the ionospheric precursors is an
artifact induced by the definition of the reference line adopted in analyzing TEC variations. We also discuss
this repeatability in the tectonic and geodynamic context of the earthquakes. By performing a Superimposed
Epoch Analysis of TEC data, we show that, however, the TEC increase reported by Heki (2011) was not
particularly anomalous. We conclude that the TEC precursors reported by Heki (2011) and Heki and Enomoto
(2013) are not useful for developing short-term earthquake prediction capabilities.2015-02-11T23:00:00ZThe IONORT-ISP-WC system: inclusion of an electron collision frequency model for the D-layer
http://hdl.handle.net/2122/9417
Title: The IONORT-ISP-WC system: inclusion of an electron collision frequency model for the D-layer
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; 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: The IONORT-ISP system (IONOspheric Ray-Tracing – IRI-SIRMUP-PROFILES) was recently developed and tested by comparing the measured oblique ionograms over the radio link between Rome (41.89ºN, 12.48ºE), Italy, and Chania (35.51ºN, 24.02ºE), Greece, with the IONORT-ISP simulated oblique ionograms (Settimi et al., 2013). The present paper describes an upgrade of the system to include: a) electron-neutral collision have been included by using a collision frequency model that consists of a double exponential profile; b) the ISP three dimensional (3-D) model of electron density profile grid has been extended down to the altitude of the D-layer; c) the resolution in latitude and longitude of the ISP 3-D model of electron density profile grid has been increased from 2°x2° to 1°x1°. Based on these updates, a new software tool called IONORT-ISP-WC (WC means with collisions) was developed, and a database of 33 IONORT-ISP-WC synthesized oblique ionograms calculated for single (1-hop paths) and multiple (3-hop paths) ionospheric reflections. The IONORT-ISP-WC simulated oblique ionograms were compared with the IONORT-IRI-WC synthesized oblique ionograms, generated by applying IONORT in conjunction with the International Reference Ionosphere (IRI) 3-D electron density grid, and the observed oblique ionograms over the aforementioned radio link. The results obtained show that (1) during daytime, for the lower ionospheric layers, the traces of the synthesized ionograms are cut away at low frequencies because of HF absorption; (2) during night-time, for the higher ionospheric layers, the traces of the simulated ionograms at low frequencies are not cut off (very little HF absorption); (3) the IONORT-ISP-WC MUF values are more accurate than the IONORT-IRI-WC MUF values.
Description: SPECIAL ISSUE: International Reference Ionosphere (IRI) and Global Navigation Satellite Systems (GNSS)2015-04-14T22:00:00ZCorrection’s method of the electron density model in ionosphere by ray tracing techniques
http://hdl.handle.net/2122/9340
Title: Correction’s method of the electron density model in ionosphere by ray tracing techniques
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Università Sapienza, Dipartimento di Fisica, p.le Aldo Moro 2, I-00185 Rome, Italy; Baskaradas, J. A.; School of Electrical & Electronics Engineering, Shanmugha Arts, Science, Technology & Research Academy (SASTRA) University, Tirumalaisamudram, Thanjavur, 613 401 Tamilnadu, India
Abstract: When applying the ray tracing in ionospheric propagation, the electron density modelling is the main input of the algorithm, since phase refractive index strongly depends on it. Also the magnetic field and frequency collision modelling have their importance, the former as responsible for the azimuth angle deviation of the vertical plane containing the radio wave, the latter for the evaluation of the absorption of the wave. Anyway, the electron density distribution is strongly dominant when one wants to evaluate the group delay time characterizing the ionospheric propagation. From the group delay time, azimuth and elevation angles it is possible to determine the point of arrival of the radio wave when it reaches the Earth surface. Moreover, the procedure to establish the target (T) position is one of the essential steps in the Over The Horizon Radar (OTHR) techniques which require the correct knowledge of the electron density distribution. The group delay time generally gives rough information of the ground range, which depends on the exact path of the radio wave in the ionosphere. This paper focuses on the lead role that is played by the variation of the electron density grid into the ray tracing algorithm, which is correlated to the change of the electron content along the ionospheric ray path, for obtaining a ray tracing as much reliable as possible. In many cases of practical interest, the group delay time depends on the geometric length and the electron content of the ray path. The issue is faced theoretically, and a simple analytical relation, between the variation of the electron content along the path and the difference in time between the group delays, calculated and measured, both in the ionosphere and in the vacuum, is obtained and discussed. An example of how an oblique radio link can be improved by varying the electron density grid is also shown and discussed.2015-03-14T23:00:00ZAutomatic interpretation of oblique ionograms
http://hdl.handle.net/2122/9339
Title: Automatic interpretation of oblique ionograms
Authors: Ippolito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Francis, M.; IPS Radio & Space Services, Bureau of Meteorology, Level 15, Tower C, 300 Elizabeth Street, Sydney, Australia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cesaroni, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: We present an algorithm for the identification of trace characteristics of oblique ionograms allowing determination of the Maximum Usable Frequency (MUF) for communication between the transmitter and receiver. The algorithm automatically detects and rejects poor quality ionograms. We performed an exploratory test of the algorithm using data from a campaign of oblique soundings between Rome, Italy (41.90 N, 12.48 E) and Chania, Greece (35.51 N, 24.01 E) and also between Kalkarindji, Australia (17.43 S, 130.81 E) and Culgoora, Australia (30.30 S, 149.55 E). The success of these tests demonstrates the applicability of the method to ionograms recorded by different ionosondes in various helio and geophysical conditions.2015-03-14T23:00:00ZIs there a one-to-one correspondence between ionospheric anomalies and large earthquakes along Longmenshan faults?
http://hdl.handle.net/2122/9336
Title: Is there a one-to-one correspondence between ionospheric anomalies and large earthquakes along Longmenshan faults?
Authors: He, L. M.; Shenyang University, China; Wu, L. X.; Normal Beijing Univ., China; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Liu, S. J.; Shenyang University, China; Yang, Y.; Shenyang University, China
Abstract: On 12 May 2008, a destructive M8.0 earthquake
struck Wenchuan County (31.0 N, 103.4E) in the Longmenshan fault zone of southwestern China. Five years later, on 20 April 2013, another terrible M7.0 earthquake struck
Lushan County (30.3 N, 103.0 E) in the same fault area, only 87 km away from the epicenter of the Wenchuan earthquake.
In this paper, an integrated wavelet analysis methodology is proposed to detect and diagnose ionospheric total electron
content (TEC) anomalies related to seismic activities.
Analytic wavelet transform is used to detect ionospheric perturbations, and then cross-wavelet analysis is used to diagnose
ionospheric anomalies by gaining further insights into the dynamic relationship between the anomaly variability of
ionospheric TEC and geomagnetic indices for the same set of observations. The results show that a significant ionospheric
disturbance occurred on 9 May 2008 above the forthcoming epicenter, 3 days prior to the Wenchuan earthquake. However,we did not observe an ionospheric anomaly over the
epicenter of the Ya’an earthquake during the 1 month period before the shock. Finally, we discuss the possible interpretations of the different seismo-ionospheric effects for the two similar earthquakes.2013-12-31T23:00:00ZOn the possible use of radio occultation middle latitude electron density profiles to retrieve thermospheric parameters
http://hdl.handle.net/2122/9210
Title: On the possible use of radio occultation middle latitude electron density profiles to retrieve thermospheric parameters
Authors: Mikhailov, A.; Izmiran, Russia; Beleaki, A.; NOA, Greece; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Tsagouri, I.; NOA, Greece
Abstract: This paper investigates possible use of middle latitude daytime COSMIC and CHAMP ionospheric radio occultation (IRO)
electron density profiles (EDPs) to retrieve thermospheric parameters, based on the Mikhailov et al. (2012) method. The aim of
this investigation is to assess the applicability of this type of observations for the routine implementation of the method. According
to the results extracted from the analysis presented here, about half of COSMIC IRO EDP observed under solar minimum
(2007–2008) conditions gave neutral gas density with an inaccuracy close to the declared absolute inaccuracy ±(10–15)% of
CHAMP observations, with the results being better than the empirical models JB-2008 and MSISE-00 provide. For the other half
of IRO EDP, either the solution provided by the method had to be rejected due to insufficient accuracy or no solution could be
obtained. For these cases, the parameters foF2 and hmF2 extracted from the corresponding IRO profiles have been found to be
inconsistent with the classic mid-latitude daytime F2-layer formalism that the method relies on, and they are incompatible with
the general trend provided by the IRI model. For solar maximum conditions (2002) the method was tested with IRO EDP from
CHAMP and it is indicated that its performance is quite stable in the sense that a solution could be obtained for all the cases
analyzed here. However available CHAMP EDP are confined by ~ 400 km in altitude and this might be the reason for the
20% bias of the retrieved densities toward larger values in respect to the observed densities. IRO observations up to 600 km under
solar maximum are required to confirm the exact performance of the method.2014-02-27T23:00:00ZComment on “The winter anomaly in the middlelatitude F region during the solar minimum period observed by the Constellation Observing System for Meteorology, Ionosphere, and Climate” by W. K. Lee, H. Kil, Y.-S. Kwak, Q. Wu, S. Cho, and J. U. Park
http://hdl.handle.net/2122/9195
Title: Comment on “The winter anomaly in the middlelatitude F region during the solar minimum period observed by the Constellation Observing System for Meteorology, Ionosphere, and Climate” by W. K. Lee, H. Kil, Y.-S. Kwak, Q. Wu, S. Cho, and J. U. Park
Authors: Mikhailov, A.; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: Seasonal or winter anomaly in the F2 layer has been known since the beginning of regular ionospheric
observations [e.g., Berkner and Wells, 1938, and references therein], and one may be sure that such a
fundamental feature of this phenomenon as its height extent has been analyzed. However, Lee et al. [2011]
using radio occultation Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)
Ne(h) observations have decided to reconsider this problem starting from the very beginning without any
analyses of previous investigations and comparisons to earlier obtained results as if ionospheric F2 layer
physics has started with them. Besides, the authors have done some incorrect statements which contradict
the present theory of the ionospheric F2 layer.
They claim that
“The topside plasma density is greater in the summer hemisphere than in the winter hemisphere;
… the electron density below the F peak at middle latitudes is also greater during summer than
during winter;
Therefore, the seasonal anomalous behavior is a phenomenon only near the F-peak height in the
Northern Hemisphere;
The question is why the seasonal behavior of the ionosphere near the F-peak height is different from the
behavior below and above the F peak.
….there was no explanation for the different seasonal behaviors of electron density in the lower F region
and at F-peak height”.
This is the main contents and results of the paper. Let us consider what was known about winter anomaly
before the paper by Lee et al. [2011].2014-09-03T22:00:00ZA method for foF2 short-term (1–24 h) forecast using both historical and real-time foF2 observations over European stations: EUROMAP model
http://hdl.handle.net/2122/9179
Title: A method for foF2 short-term (1–24 h) forecast using both historical and real-time foF2 observations over European stations: EUROMAP model
Authors: Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Mikhailov, A.
Abstract: A method for foF2 short-term forecast over Europe has been developed and implemented in
the EUROMAP model. The input-driving parameters are 3 h ap indices (converted to ap(τ)), effective
ionospheric T index, and real-time foF2 observations. The method includes local (for each station)
regression storm models to describe strong negative disturbances under ap(τ)>30 and training models to
describe foF2 variations under ap(τ) ≤ 30. The derived model was tested in two regimes: descriptive when
observed 3 h ap indices were used and real forecast when predicted daily Ap were used instead of 3 h ap
indices—. In the case of strong negative disturbances the EUROMAP model demonstrates on average the
improvement over the lnternational Reference Ionosphere STORM-time correction model (IRI(STORM))
model: 40% in winter, 24% in summer, and 39% in equinox. The average improvement over climatology is
41% in winter, 59% in summer, and 55% in equinox. In the majority of cases this difference is statistically
significant. In the case of strong positive disturbances, higher-latitude stations also manifest a significant
difference between the twomodels but this difference is insignificant at lower latitude stations. The substitution
of 3 h ap input indices for the predicted daily Ap ones decreases the foF2 prediction accuracy in the case of
negative disturbances but practically has no effect with positive disturbances. In both cases the proposed
method manifests better accuracy than the IRI(STORM) model provides. The obtained results show a real
opportunity to provide foF2 forecast with the (1–24 h) lead time on the basis of predicted Ap indices2014-04-09T22:00:00ZSporadic 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.2014-10-22T22:00:00Z