Carlo Scotto

Estimating the vertical electron density profile from an ionogram: on the passage from true to virtual heights via the target function method

[1] The paper describes a new simple method of calculation by which an artificial ionogram trace is obtained from a given vertical electron density profile. The method is discussed in terms of the target function method used by Autoscala to output a reliable estimation of the real vertical electron density profile associated to the recorded ionogram. This new approach solves the issue of the pole in the calculation of virtual height, and consequently eliminates all the divergence phenomena that sometimes characterized the artificial ionogram traces computed by Autoscala. In contrast to the POLAN procedure, the technique introduced in this paper to pass from true to virtual heights is not based on any arithmetical operation related to changes of integration variables. Since the target function method on which Autoscala is based requires that the passage from a vertical electron density profile to an artificial ionogram be repeated a very large number of times, this new calculation procedure is advantageous in terms of speeding up the associated processing time.

A method to test HF ray tracing algorithm in the ionosphere by means of the virtual time delay

As well known a 3D ray tracing algorithm furnishes the rays coordinates, the three components of the wave vector and the group time delay of the wave along the path. This last quantity can be compared with the measured group delay to check the performance of the algorithm. Simulating a perfect reflector at an altitude equal to the virtual height of reflection the virtual delay is assumed as a real group delay. For a monotonic electronic density profile we find a very small relative difference between the calculated and the simulated delay both for analytic and discrete 3D electronic density models.

Scientific Review on the Ionospheric Absorption and Research Prospects of a Complex Eikonal Model for One-Layer Ionosphere

The present 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.

Variability of foF2 over Rome and Gibilmanna during three solar cycles (1976‐2000)

[1]xa0Hourly validated values of the F2-layer critical frequency (foF2) recorded at Rome, Italy (geographic coordinates 41.8°N, 12.5°E; geomagnetic coordinates 42.0°N, 93.8°E), and Gibilmanna, Italy (geographic coordinates 37.6°N, 14.0°E; geomagnetic coordinates 38.1°N, 93.6°E), along with the hourly quiet time reference values of foF2 (foF2QTRV) were considered around periods of minimum and maximum solar activity over the years 1976–2000. The foF2 data set was specifically organized in order to obtain an overall trend both for low and high solar activity, and different dispersion indices were used. The results obtained show that (1) at Rome, the foF2 variability is always greater during periods of high solar activity (HSA) in the hourly ranges 00:00–02:00 UT and 20:00–23:00 UT during winter months, and in the hourly ranges 00:00–10:00 UT and 04:00–16:00 UT during equinoctial and summer months respectively; (2) on the whole, around midday, for low solar activity (LSA), the foF2 variability is smaller at the equinoxes than at the solstices; for HSA, it is greater at equinoxes than at solstices; (3) for LSA, at Gibilmanna the foF2 variability is in general larger than at Rome, especially in summer, and it is characterized by a number of relative minimums and maximums greater than those observed at Rome; (4) at Rome, for both LSA and HSA, the passage of solar terminator at sunset significantly affects ionospheric variability in January, April, August, and November, at Gibilmanna in August, September, and November; (5) several variability peaks before sunrise and after sunset are observed in both stations; (6) on a monthly basis, for both LSA and HSA, a semiannual variation of foF2 variability is observed at both Rome and Gibilmanna; and (7) evidence of ionospheric variability at the typical heights of the F region, connected to upward propagating gravity waves triggered by solar terminator, is observed at Rome during some days characterized by HSA in the equinoctial months.

The effect of collisions in ionogram inversion

Abstract The results of this paper demonstrate that the effect of collisions on the group refraction index is small, when the ordinary ray is considered. If, however, in order to improve the performance of a system for automatic interpretation of ionograms, the information contained in ordinary and extraordinary traces is combined, the effect of collisions between the electrons and neutral molecules should be taken into account for the extraordinary ray. The magnitude of these differences is generally very small and must be compared with the resolution in the virtual vertical height of the ionosonde, resolution which is typically of the order of few kilometers.

A procedure for the reliability improvement of the oblique ionograms automatic scaling algorithm

A procedure made by the combined use of the Oblique Ionogram Automatic Scaling Algorithm (OIASA) and Autoscala program is presented. Using Martyns equivalent path theorem, 384 oblique soundings from a high-quality data set have been converted into vertical ionograms and analyzed by Autoscala program. The ionograms pertain to the radio link between Curtin W.A. (CUR) and Alice Springs N.T. (MTE), Australia, geographical coordinates (17.60°S; 123.82°E) and (23.52°S; 133.68°E), respectively. The critical frequency foF2 values extracted from the converted vertical ionograms by Autoscala were then compared with the foF2 values derived from the maximum usable frequencies (MUFs) provided by OIASA. A quality factor Q for the MUF values autoscaled by OIASA has been identified. Q represents the difference between the foF2 value scaled by Autoscala from the converted vertical ionogram and the foF2 value obtained applying the secant law to the MUF provided by OIASA. Using the receiver operating characteristic curve, an appropriate threshold level Qt was chosen for Q to improve the performance of OIASA.

A procedure for the automatic scaling of oblique ionograms

In this work we present a method 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. An exploratory test of the algorithm has been performed using data from a campaign of oblique soundings between the ionosondes of Rome, Italy (41.90 N, 12.48 E) and Chania, Greece (35.51 N, 24.01 E) and also between the ones of 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-geophysical conditions.

A regional adaptive and assimilative three-dimensional ionospheric model

A regional adaptive and assimilative three-dimensional (3D) ionospheric model is proposed. It is able to ingest real-time data from different ionosondes, providing the ionospheric bottomside plasma frequency ƒ p over the Italian area. The model is constructed on the basis of empirical values for a set of ionospheric parameters P i[base] over the considered region, some of which are assigned a variation ΔP i . The values for the ionospheric parameters actually observed at a given time at a given site will thus be P i = P i[base] +ΔP i . These P i values are used as input of an electron density N(h) profiler. The latter is derived from the Advanced Ionospheric Profiler (AIP), which is software used by Autoscala as part of the process of automatic inversion of ionogram traces. The 3D model ingests ionosonde data by minimizing the root-mean-square deviation between the observed and modeled values of ƒ p (h) profiles obtained from the associated N(h) values at the points where observations are available. The ΔP i values are obtained through such a minimization procedure. The 3D model is tested using data collected at the ionospheric stations of Rome (41.8 N, 12.5 E) and Gibilmanna (37.9 N, 14.0 E), and then comparing the results against data from the ionospheric station of San Vito dei Normanni (40.6 N, 18.0 E). The software developed is able to produce maps of the critical frequencies ƒ o F 2 and ƒ o F 1 , and of ƒ p at a fixed altitude, with transverse and longitudinal cross-sections of the bottomside ionosphere in a color scale. ƒ p (h) and associated simulated ordinary ionogram traces can easily be produced for any geographic location within the Italian region. ƒ p values within the volume in question can be also provided.

Thunderstorm-related variations in the sporadic E layer around Rome

Superposed epoch analysis (SEA) was used to study possibly statistically significant variations of the critical frequency (foEs) and virtual height (h’Es) of the sporadic E layer (Es) related to thunderstorm activity generated in the troposphere. The reference time for the SEA was the time of lightning strokes measured by the World Wide Lightning Location Network at the ionosonde station of Rome (41.9