Sporadic E layer at mid-latitudes: average properties and influence of atmospheric tides

Abstract

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.

On the influence of solar activity on the mid-latitude sporadic E layer

“…The data set considered in this study is constituted by hourly values of foEs and fbEs recorded at the ionospheric station of Rome (41.8°N, 12.5°E), Italy, from January 1976 to December 2009, and validated according to the URSI (International Union of Radio Science) standard (Piggott & Rawer 1972). Data were downloaded from the electronic Space Weather upper atmosphere (eSWua) database (http://www.…”

“…We focused our attention on the mean around 12:00 LT, because it is known that mid-latitude Es layers present a maximum of electron density right around this local time hour (i.e. Bossolasco & Elena 1963;Pignalberi et al 2014). Table 2 shows the occurrence percentage of the various types of Es traces, l(ow), c(usp) and h(igh), recorded between 10:00 LT and 14:00 LT, for the whole data set from January 1976 to December 2009.…”

“…The latter, thanks to a combined action of the ion-neutral collisional coupling and the geomagnetic Lorentz force, trigger the long-lived metallic ions produced by the continuous meteoric shower activity to move vertically into the convergence node of the neutral horizontal wind vertical profile, thus forming dense and narrow ionization layers. More specifically, it has been found that the appearance and intensity of mid-latitude Es layers is influenced by vertical wind shears related to tidal waves, gravity waves and planetary waves, that compel the metallic and molecular ions into thin layers at altitudes from 95 to 120 km (Chimonas 1971;MacDougall 1974;Wilkinson et al 1992;Szuszczewicz et al 1995;Tsunoda et al 1998;Haldoupis & Pancheva 2002;Haldoupis et al 2004;Pignalberi et al 2014Pignalberi et al , 2015.…”

20 March 2015 solar eclipse influence on sporadic E layer

“…Hence, from a single ionogram it would not be possible to derive the dynamics of the ionospheric layers. On the contrary, the HTI analysis proposed by Haldoupis et al (2006), and recently used by Pignalberi et al (2014) and Oikonomou et al (2014), to investigate how tidal waves influence the Es dynamics, considers a specific frequency range and, by using a series of ionograms, allows the study of the aforementioned dynamics. The output of the HTI analysis is a plot of the intensity of the energy received by the ionosonde, after being reflected by the ionosphere, versus the 24 h of the day, for a definite frequency range, and for the same height range of the ionogram.…”

Mid Latitude Sporadic E-layer Variability during Ascending Phase of Solar Cycle 24

“…Observations revealed that the diurnal and semidiurnal tides are the main agents that control the formation and altitude descent of sporadic E layers. Pignalberi et al also used height-time-intensity (HTI) which describe the daily variability of the sporadic E (Es) layer, the top frequency (ftEs) and the lowest virtual height (h'Es) [18,19]. The height-time-Intensity (HTI) study, along with a fast Fourier transform analysis, showed that a semidiurnal periodicity characterizes the Es layer 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.…”