Abstract
Abstract. The goal of this work is to investigate the gravity wave (GW) characteristics in the low ionosphere using very low frequency (VLF) radio signals. The spatial modulations produced by the GWs affect the conditions of the electron density at reflection height of the VLF signals, which produce fluctuations of the electrical conductivity in the D region that can be detected as variations in the amplitude and phase of VLF narrowband signals. The analysis considered the VLF signal transmitted from the US Cutler, Maine (NAA) station that was received at Comandante Ferraz Brazilian Antarctic Station (EACF, 62.1∘ S, 58.4∘ W), with its great circle path crossing the Drake Passage longitudinally. The wave periods of the GWs detected in the low ionosphere are obtained using the wavelet analysis applied to the VLF amplitude. Here the VLF technique was used as a new aspect for monitoring GW activity. It was validated comparing the wave period and duration properties of one GW event observed simultaneously with a co-located airglow all-sky imager both operating at EACF. The statistical analysis of the seasonal variation of the wave periods detected using VLF technique for 2007 showed that the GW events occurred all observed days, with the waves with a period between 5 and 10 min dominating during night hours from May to September, while during daytime hours the waves with a period between 0 and 5 min are predominant the whole year and dominate all days from November to April. These results show that VLF technique is a powerful tool to obtain the wave period and duration of GW events in the low ionosphere, with the advantage of being independent of sky conditions, and it can be used during the whole day and year-round.
Highlights
The upper part of the middle atmosphere, the upper mesosphere and lower thermosphere (MLT), is dominated by the effects of the atmospheric waves with periods from a few seconds to hours, which originate at tropospheric and stratospheric layers or even from in situ generation
In this work we presented an investigation of the gravity wave (GW) characteristics in the low ionosphere, where they produce density fluctuations that were detected as amplitude variations of very low frequency (VLF) signals
The analysis used the VLF signal transmitted from the US Cutler, Maine (NAA) station that was received at Comandante Ferraz Brazilian Antarctic Station (EACF), with a great circle path crossing the Drake Passage longitudinally
Summary
The upper part of the middle atmosphere, the upper mesosphere and lower thermosphere (MLT), is dominated by the effects of the atmospheric waves (acoustic–gravity waves, gravity waves, tides and planetary waves) with periods from a few seconds to hours, which originate at tropospheric and stratospheric layers or even from in situ generation. The ionospheric absorption modulations observed with different riometer beams permit one to infer the gravity wave parameters such as the phase velocity, period, and direction of propagation, as demonstrated by Jarvis et al (2003) and MoffatGriffin et al (2008) They validated this technique comparing mesospheric GW signatures observed by using both a colocated imaging riometer and airglow imager. The purpose of this paper is to present the characterization of the GW events detected in the lower ionosphere from the analysis of the VLF NB amplitude of signals detected at Comandante Ferraz Brazilian Antarctic Station (EACF) The wave parameters such as the period and the time duration of the GW activity will be obtained from the spectral analysis of the VLF amplitude fluctuations. The methodology using the VLF technique is validated comparing the derived parameters of one GW event detected simultaneously with a co-located airglow all-sky imager
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