A spectral study of the mid-latitude sporadic E layer characteristic oscillations comparable to those of the tidal and the planetary waves

Abstract

In this paper different spectral analyses are employed to investigate the tidal and planetary wave peri-odicities imprinted in the following two main characteristics of the sporadicE(Es)layer: the top fre-quency (ftEs) and the lowest virtual height(h′Es). The study is based on ionograms recorded during the summertime of 2013, and precisely in June, July, August and September, by the Advanced Ionospheric Sounder by Istituto Nazionale di Geofisica e Vulcanologia (AIS-INGV) ionosondes installed at Rome (41.8°N, 12.5°E) and Gibilmanna (37.9°N, 14.0°E), Italy. It was confirmed that the diurnal and semidiurnal atmospheric tides play a fundamental role in the formation of the mid-latitude Eslayers, acting through their vertical wind-shear forcing of the long-living metallic ions in the lower thermosphere, and at the same time it was found that the planetary atmospheric waves might affect the Es layers acting through their horizontal wind-shear forcing with periods close to the normal Rossby modes, that is 2, 5, 10 and 16 days. The wavelet analysis shows also that the ftEs and h′Es tidal oscillations undergo a strong amplitude modulation with periods of several days and with important differences between the two parameters. This amplitude modulation, characterizing markedly the first thirty days of the ftEs spectrogram, suggests that Es layers areaffected indirectly by planetary waves through their nonlinear interaction with the atmospheric tides at lower altitudes. This study wants to be a continuation of the Haldoupis et al.(2004) work in order to verify their results for the foEs characteristic and on the other hand to extend the study also to the h′Es characteristic not yet shown so far. Anyhow, the study confirms that ionosonde data, especially those registered in summertime, represent a powerful tool for studying tidal and planetary waves properties and their climatology in the mesosphere–low-thermosphere region.