Meteor radar observations at São João do Cariri (7.4°S; 36.5°W), Cachoeira Paulista (22.7°S; 45°W) and Santa Maria (29.7°S; 53.7°W) have permitted estimates to be made of winds in the mesosphere and lower thermosphere (MLT) over the Brazilian sector simultaneously. Using horizontal winds the semidiurnal lunar tide is determined from January 2005 to December 2008 for these three sites. The lunar tide is observed to reach amplitudes as large as 8m/s. In general, the amplitude increases with height and the phase decreases with height, corresponding to an upwardly-propagating tide. The estimated vertical wavelengths are variable for some month, like December at Cachoeira Paulista for northward wind, April and June at Santa Maria for eastward wind, which indicates possible mode coupling and reflection. Characteristics similar to those seen in the Northern Hemisphere have been observed in June and October at São João do Cariri, in December at Cachoeira Paulista, in March at Santa Maria and in August at all observation sites, which suggest the presence of antisymmetric modes. Different behavior has been observed in the amplitudes, phases and vertical wavelengths at each station, indicating latitudinal variation even from the low to the equatorial region.

The possible existence of a positron radiation belt in the inner magnetosphere of the Earth, its space location, flux, energy distribution and the ratio of e+/e− fluxes is considered. The source of the positrons/electrons is assumed to be the decay of charged pions (π - μ - e decay chain) produced, in the nuclear interactions between protons and the neutral constituents of the atmosphere. The production of excess positron fluxes over electron ones through this process is examined for two different proton populations and their atmospheric interactions in the altitude range of 80 to 1000 km. Monte Carlo simulations of intranuclear cascade process through SHIELD code was utilized to simulate these interactions. Considering the trapped proton fluxes in the inner magnetosphere as a source, the simulations for interactions in rarified atmosphere shows excess of positrons over electrons with ratios above 2 for proton energies below 2.5 GeV. Although, protons above this energy do not produce excess of positrons compared to electrons in atmospheric interactions, we assumed the primary cosmic rays with the energy greater than 8–10 GeV also as a source for these interactions, and utilizing the east-west asymmetry in the arrival directions of these primary cosmic rays combined with the exponential nature of the atmosphere density we also obtained an excess of positrons over electrons escaping from the atmosphere to the altitudes of satellite orbits. A comparison is attempted with the recent data of AMS experiment on board the space shuttle.

Meteor radar observations at São João do Cariri (7.4°S, 36.5°W), Cachoeira Paulista (23°S, 45°W) and Santa Maria (29.7°S, 53.7°W) have permitted estimates to be made of winds and temperature in the mesosphere and lower thermosphere (MLT). Using horizontal winds the lunar semidiurnal tide was determined from January 2005 to December 2008 for these three sites. In January 2006 an unusual enhancement was observed in the lunar tide amplitude at these stations, for meridional and zonal components. During this period, sudden stratospheric warming (SSW) events were observed in the northern hemisphere. Meridional and zonal winds observed in Brazil showed evidence of SSW effects in the MLT region. Moreover, the mesospheric temperatures at Cachoeira Paulista and Santa Maria presented cooling and a semimonthly oscillation, which followed the new–full–new moon phases. These results suggest that the enhancement of the lunar tide could be a response for the SSW in the MLT.

The Transient Luminous Events (TLEs) are light emissions that occur in middle and upper atmosphere and are associated with thunderstorms with high electrical activity. Usually these events are associated with electric fields produced in the occurrence of lightning. On March 04th, 2006 sprites and halos were observed above a storm over Paraguay from the Southern Space Observatory - SSO/CRS/INPE-MCT, (29.4°S, 53.8°W, 480 m a.s.l.), São Martinho da Serra, RS, Brazil, during a field campaign. The formation of the mesoscale convective system that gave rise to the TLEs was favored by a combination of factors. The confluence of the north and south low level jets, the north carrying hot air and humidity from the Amazon, and the south carrying cold air from the frontal system to the region of formation of the storm, associated with high upward vertical velocity were fundamental to the development of MCS over Paraguay. 94 sprites were observed in this campaign, the majority occurred during the apex of the MCS, when the system had its larger area of clouds Cumulunimbus. This work shows the weather conditions that favored the formation of the MCS generating TLEs, and relate the TLEs observation with the development stages of the MCS.

Using the variance in meteor radar winds as a measure of gravity wave activity, we investigate the temporal variations in gravity waves at three locations in Brazil: São João do Cariri (7.3° S, 36.4° W), Cachoeira Paulista (22.7° S, 45.0° W) and Santa Maria (29.7° S, 53.7° W). The technique used is that of Hocking (2005) which makes it possible to separate the zonal and meridional components of the fluctuating wind velocity. We find that the seasonal variation of the fluctuating wind is similar to that of the amplitude of the diurnal tide, showing a predominantly semi-annual variation, stronger at Cachoeira Paulista and Santa Maria than at the quasi-equatorial station, Cariri. Both with respect to the seasonal trend and shorter term variations, strong coupling between gravity wave activity and tides is indicated by a remarkably close correlation between the fluctuating velocity and the vertical shear in the tidal winds. It is not clear as to whether this is caused by gravity wave forcing of the tides or whether it results from in situ generation of gravity waves by tidal wind shear.

Meteor radar wind measurement at Cariri (7.4°S, 36.5°W) and Ionosonde measurements at Fortaleza(3.9°S, 38.4°W) have been carried out in 2005. 3 to 5 days period oscillations in the mesospheric zonal wind and ionospheric F-layer bottom height (h’F) and the maximum frequency (foF2) were observed during a period from March 01 to 11, 2005. Atmospheric temperatures observed by the SABER/TIMED satellite also showed a similar periodic oscillations. From the characteristics of the downward phase propagation, longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5–day Ultra Fast Kelvin (UFK) wave. The observed amplitude of oscillation of the F-layer height caused by the UFK waves, 20–30 km, are significant, and worthwhile to investigate in terms of the day to day variability of the Spread F occurrence.

A secondary proton radiation belt can be observed in the equatorial region between the upper atmosphere and the interior edge of the main radiation belt. It is thought that the protons appear there in a result of ionization of energetic neutral hydrogen atoms coming from the internal area of the traditional radiation belt where they were born in charge exchange collisions of the trapped protons with the cold hydrogen of the gecorona. The process of formation of this secondary belt is numerically simulated in this paper assuming this charge exchange-reionization mechanism. Standard models of the trapped radiation, of the atmosphere and geocorona were used to simulate the source and the exospheric media. Experimental data were used for charge transfer cross sections. Result of simulation agrees very good with the experimental observation.

The possible existence of noticeable fluxes of antiparticles in the Earth magnetosphere is predicted on theoretical considerations here. We present the computational results of 50 MeV to several GeV antiproton fluxes produced from the CR particle interactions with the matter in the interstellar space and the residual atmosphere at altitudes of ∼1000 km over the Earth’s surface. The estimates shows the magnetospheric antiproton fluxes are greater by two orders of magnitude compared to the interstellar fluxes measured at energies >1 GeV.

The possible existence of noticeable fluxes of antiparticles in the Earth magnetosphere has been predicted on theoretical considerations in this article. The antiprotons expected at several hundred kilometers of altitudes, we do not believe are of direct extraterrestrial origin, but are the natural products of nuclear reactions of the high‐energy primary cosmic rays (CR) with the constituents of the terrestrial atmosphere. Extraterrestrial, galactic antiprotons are themselves of secondary in origin, i.e. they are born in nuclear reactions of the same CR particles passing through 5–7 g/cm 2 of interstellar matter encountered during their lifetime in the Galaxy. We expect that the fluxes of magnetospheric antiprotons to be higher compared to the interstellar fluxes because the fluxes get accumulated due to confinement by the magnetic field of the Earth. We present the results of the computations of the antiproton fluxes at 50 MeV to several GeV energies due to the CR particle interactions with the matter in the interstellar space, and also with the residual atmosphere at altitudes of ∼1000 km over the Earth's surface. The estimates show that the magnetospheric antiproton fluxes are two orders of magnitude greater compared to the interstellar fluxes measured at energies < 1 GeV.