C. M. Wrasse

Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting

Equatorial 3.5-day ultra-fast Kelvin wave was observed in the MLT zonal wind measured by meteor radar at Cariri (7.4°S, 36.5°W, geomag. 8°S) and in the stratosphere-mesosphere temperature structures from the TIMED/SABER data. The ionospheric F-layer bottom-side virtual height hT’F and the critical frequency foF2 observed at Fortaleza (3.9°S, 38.4°W, geomag. 5°S) also showed similar oscillation structures, indicating an influence of the Kelvin wave in the F region height and modulation of E × B uplifting during the evening period. Consequently the ionospheric spread F onset time was also modulated in the same period, around 4 days.

Ionospheric TEC weather map over South America

Ionospheric weather maps using the total electron content (TEC) monitored by ground based GNSS receivers over South American continent, TECMAP, have been operationally produced by INPE´s Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial, EMBRACE) since 2013. In order to cover the whole continent, 4 GNSS receiver net-works, RBMC/IBGE, LISN, IGS and RAMSAC, in total ~140 sites, have been used. TECMAPs with a time resolution of 10 minutes are produced in 12 hour time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day to day variabilities of the equatorial ionization anomaly (EIA) have been observed. Spatial gradient of TEC from the anomaly trough (TECu  80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles (IPB), their seeding and development, could be monitored.These plasma density (spatial and temporal) variability causes not only the GNSS based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC Mapping becomes an important issue for Space Weather concern for high technology positioning system and telecommunication.

Atmospheric wind effects on the gravity wave propagation observed at 22.7° S-Brazil

Abstract An all-sky CCD imager for the airglow OH, O 2 and OI (557,7 nm) measurements was operated at Cachoeira Paulista (22.7°S, 45.0°W) from September 1998 to August 1999. Dominant gravity wave events were extracted and studied. It is found that the horizontal wavelengths are typically from 5 to 60 km and the period from 5 to 35 minutes with the horizontal phase speed of 1 to 80 m/s. A ray tracing technique was applied in order to find out the gravity wave sources and to investigate the propagation of these waves through the atmosphere. The CIRA-86 reference zonal wind and temperature models and the GSWM-02 tidal wind model were used as the background condition in the present analysis. The tidal wind strongly affects the gravity wave propagation and miss-leads the location of the wave source. The major part of the tropospheric sources of the gravity waves is located 400 km around the observation site, and these sources were related with the lightning activity that is associated with strong tropospheric convection.

Determinação dos parâmetros de ondas de gravidade através da análise espectral de imagens de aeroluminescência

The airglow layers are very useful to study and monitor the temperature and wave activity in the mesosphere region. All-sky cameras have been used to observe the nightglow emissions and to investigate the gravity waves characteristics and horizontal structures. The present paper describes the methodology used to estimate the gravity wave parameters such as the horizontal wavelength, phase speed, period and propagation direction, observed in the airglow images.

Atmospheric scattering effects on ground‐based measurements of thermospheric vertical wind, horizontal wind, and temperature

Ground-based Fabry-Perot interferometers (FPIs) routinely observe large vertical winds in the thermosphere, sometimes reaching over 100 m/s. These observations, which use the Doppler shift of the 630.0-nm airglow emission to estimate the wind, have long been at odds with theory. We present a summary of 5 years of data from the North American Thermosphere-Ionosphere Observing Network (NATION), showing that large apparent vertical winds are a persistent feature at midlatitudes during geomagnetic storms. We develop a radiative transfer model which demonstrates that these measurements can be explained as an artifact of the scattering of light in the troposphere. In addition to the example from midlatitudes, we apply the model to low latitudes, where we show that the post-sunset vertical winds routinely measured over Brazil are explained in part by atmospheric scattering. Measurements of the horizontal wind and temperature are also affected, with errors reaching 400 m/s and 200 K in the most extreme cases.

Mesosphere–Ionosphere Coupling Processes Observed in the F Layer Bottom-Side Oscillation

During the Spread FEx campaign, under the NASA Living with a star (ILWS) program which was carried out in the South American Magnetic Equatorial region from September to November 2005, we observed formation of the bottom-type spread F and simultaneous occurrence of mesospheric gravity wave events. The events were monitored by the ionosonde, coherent radar and airglow OI 630.0 nm and OH imager. It is found that the bottom-type scattering layer has a wave form generated most probably by local gravity waves. Reverse ray-tracing of the observed gravity waves indicate their possible sources in the troposphere or thermosphere. Forward ray-tracing indicates their penetration into the ionosphere. The present work summarizes the observational evidence and results of the data analysis and discusses the mesosphere–ionosphere coupling processes.

Lunar tides in total electron content over Brazil

Using data from Global Navigation Satellite Systems dual frequency receivers, the lunar tides were studied in the ionospheric Total Electron Content (TEC) over Brazil from 2011 to 2014. In order to calculate the amplitudes and phases of the lunar tides, quiet magnetic days within a 27-day (window) has been used to remove the solar rotation effects. Relative residuals TEC were calculated by performing a spectral analysis by removing the solar tide contributions. Lastly, a lunar month size window was used to calculate the amplitude and phase of the lunar components. Lunar diurnal tide amplitudes showed a semiannual variation with maximum in the equinox months for almost all latitudes, while, lunar semidiurnal amplitudes were larger in December and January and may be related to sudden stratospheric warming events. Both components did not display significant longitudinal variation what could be due to the short range of longitude (30 degrees). Lunar diurnal amplitudes were basically uniform over Brazil, while lunar semidiurnal amplitudes showed some peaks over the equatorial ionization anomaly crest and minimum values near the magnetic equator.