The main purpose of this study is to investigate the vertical coupling between the mesosphere and lower thermosphere (MLT) region and the ionosphere through ultra-fast Kelvin (UFK) waves in the equatorial atmosphere. The effect of UFK waves on the ionospheric parameters was estimated using an ionospheric model which calculates electrostatic potential in the E-region and solves coupled electrodynamics of the equatorial ionosphere in the E- and F-regions. The UFK wave was observed in the South American equatorial region during February–March 2005. The MLT wind data obtained by meteor radar at São João do Cariri (7.5° S, 37.5° W) and ionospheric F-layer bottom height (<I>h</I>'F) observed by ionosonde at Fortaleza (3.9° S; 38.4° W) were used in order to calculate the wave characteristics and amplitude of oscillation. The simulation results showed that the combined electrodynamical effect of tides and UFK waves in the MLT region could explain the oscillations observed in the ionospheric parameters

Abstract. From nocturnal variations of the airglow O 2 (0-1) and OH Meinel (6-2) band emission intensity and the rotational temperature, gravity waves and the damping effect in the MLT region were investigated. The data set was obtained from photometer measurements at Rikubetsu (43.5 • N, 143.8 • E), Japan, from March 2004 to August 2005. The ratio of the amplitude of oscillation and their phase difference between the two emissions were calculated when simultaneous periodic variations were observed. The ratio showed a linear correlation with the phase difference. The vertical wavelength and damping rate were estimated by using a model calculation carried out by previous works. The results show that the wave damping is significant when the vertical wavelength is shorter than 30-40 km. Krassovsky's parameter η, which represents a ratio between the emission intensity and temperature oscillations, was also calculated. The results show that the η also depends on the damping effect.

Abstract. The main purpose of this study is to investigate the four-peak structure observed in the low-latitude equatorial ionosphere by the FORMOSAT/COSMIC satellites. Longitudinal distributions of NmF2 (the density of the F layer peak) and hmF2 (ionospheric F2-layer peak height) averages, obtained around September equinox periods from 2007 to 2015, were submitted to a bi-spectral Fourier analysis in order to obtain the amplitudes and phases of the main waves. The four-peak structure in the equatorial and low-latitude ionosphere was present in both low and high solar activity periods. This kind of structure possibly has tropospheric origins related to the tidal waves propagating from below that modulate the E-region dynamo, mainly the eastward nonmigrating diurnal tide with wavenumber 3 (DE3, "E" for eastward). This wave when combined with the migrating diurnal tide (DW1, "W" for westward) presents a wavenumber-4 (wave-4) structure under a synoptic view. Electron densities observed during 2008 and 2013 September equinoxes revealed that the wave-4 structures became more prominent around or above the F-region altitude peak ( ∼ 300-350 km). The four-peak structure remains up to higher ionosphere altitudes (∼ 800 km). Spectral analysis showed DE3 and SPW4 (stationary planetary wave with wavenumber 4) signatures at these altitudes. We found that a combination of DE3 and SPW4 with migrating tides is able to reproduce the wave-4 pattern in most of the ionospheric parameters. For the first time a study using wave variations in ionospheric observations for different altitude intervals and solar cycle was done. The conclusion is that the wave-4 structure observed at high altitudes in ionosphere is related to effects of the E-region dynamo combined with transport effects in the F region.

No abstract

ABSTRACT. In this work, the Krassovsky's η parameter, was used to investigate the amplitudes and phases of periodic variations of O 2 (0-1) and OH(6-2) airglow emissions. The data set was obtained from photometer measurements at Rikubetsu (43.5 • N, 143. Palavras-chave: parâmetro η de Krassovsky, aeroluminescência, ondas de gravidade.