Characterization of gravity wave events detected in the low ionosphere at the Brazilian Antarctic Station

Abstract

Here we present the characteristics of three distinct types of Gravity Wave (GW) events as detected in the low ionosphere using very low frequencies (VLF) radio measurements performed at the EACF, Brazilian Antarctic Station Comandante Ferraz (62° 5′ 6″ S, 58° 24′ 12″ W), on King George Island. GWs in the low ionosphere produce oscillations in the electron density, which can be detected as amplitude and phase fluctuations of the VLF signals. The properties of the GW events are obtained using Morlet's Wavelet analysis, which gives the period of the waves, and their occurrence time. The period and duration of the GW events obtained using the VLF technique presented good agreement with ones previously obtained from airglow observations from a co-located all-sky imager. The VLF detection of the mesospheric front showed the same morphology seen with the imager with four crests identified, and the wave activity presented similar period range (∼4–16 min) as observed by airglow (∼6 min) with a period peak of 14 min equal to the spectral analysis of the concurrent OH temperature data. The activity associated with the band event presented similar period of ∼10 min (imager observed 13 min), same duration of 4 h as well as peak intensity just before 05:00 UT. The ripple detection showed the same period of 8 min as the airglow observations and similar duration of around 25 min. By considering two distinct VLF paths it was also possible to analyze the direction and velocity of propagation for the mesospheric front event, which gives 96.0 (±4.8) ms⁻¹ in the East direction in agreement with the velocity of ∼92 ms⁻¹ in the Northeast direction obtained from the airglow observations.