Inacio M. Martin

Microwave properties of EPDM/PAni-DBSA blends

Conductive elastomer blends of ethylene-propylene-diene rubber, EPDM, and polyaniline, PAni, doped with dodecylbenzene sulfonic acid, DBSA, were prepared and evaluated as a radar absorbing material, RAM. Reflectivity measurements in the 8-12 GHz frequency range, using the NRL arch method, were done to evaluate the shielding effectivity. The results showed that the dopant and PAni concentrations and also the sample thickness affect these measurements. Good shielding values were obtained (-15 dB) with the 50/50, 40/60 and 20/80 (w/w %) EPDM/PAni blends.

Rainfalls during great Forbush decreases

SummaryThe changes of rainfall values during great Forbush decreases recorded by the low-latitudinal neutron monitor of Huancayo (47 events from 1956 through 1992) were examined. The data on precipitations were taken from the State of São Paulo and from the Amazonian region, Brazil. As a rule, the data from more than 50 meteorological stations were used for each events. The main result is the following: during strong decreases of cosmic-ray flux in the atmosphere (great Forbush decreases) the precipitation value is decreased. The effect of rainfall changes is seen more distinctly if wet seasons are considered.

Nuclear reactions in the uppermost Earth atmosphere as a source of the magnetospheric positron radiation belt

A physical mechanism for the formation of a natural positron belt in the Earths magnetosphere is considered. It is assumed that a natural source of energetic positrons as well as electrons can be created owing to the decay of charged pions π± → μ± → e±, which have their origin in nuclear collisions between energetic trapped inner zone protons and heavier atoms (He and O) in the upper atmosphere of the Earth. Simulations of these processes demonstrate that there is a predominant production of positive pions over negative pions, and consequently the decays result in a substantial excess of positrons over electrons at energies greater than tens of MeV. This positron excess is found to be energy-dependent and to decrease with increasing incident proton energy; this excess is essentially absent at proton energies corresponding to cosmic ray primaries of ≥8 GeV. Our numerical computations for the resulting e+/e− fluxes provide ratio values of ∼4 at multi-MeV energies and at L = 1.2 ± 0.1. The simulation results presented herein are compared to the existing and recent experimental evidence.

Dynamics of the low‐altitude energetic proton fluxes beneath the main terrestrial radiation belts

At the interface between the upper atmosphere and the radiation belt region there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and in the main radiation belt and then re-ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64–35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the 3-year period from February 21, 1984, to March 26, 1987, using data obtained with the High-Energy Particle experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of ∼1.2 cm−2 s−1 sr−1 was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically 2 orders of magnitude). These flux decreases were also long in duration (lasting up to 3 months). We also registered abrupt flux increases, such that magnitude of the proton flux enhancements could reach 3 orders of magnitude and with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.

Electron precipitation associated with geomagnetic activity: Balloon observation of X ray flux in South Atlantic anomaly

A stratospheric balloon experiment was conducted on December 20, 1994, with an X ray detector to measure fluxes of precipitation electrons in the South Atlantic anomaly (SAA) region of Brazil. For the first time in the SAA, this detector system of high sensitivity monitored three events of increases in X ray fluxes which axe associated with simultaneous decreases in geomagnetic H field component. The most prominent event with an X ray emission equivalent to ≈1/4 of the diffuse cosmic X ray flux permitted the determination of the spectrum in the energy range of 18.6 to 120 keV. The inferred electron spectrum showed a steep low-energy component below 150 keV (E0=16 keV). The electron flux estimates are lower compared to earlier balloon results obtained at the time of a severe magnetic storm. The inferred fluxes from our balloon experiment are consistent with the electron fluxes observed by the S3–2 satellite and are lower than the OGO 5 satellite measurements, both obtained in the SAA at L= 1.3. Further, the estimates are compatible with the P78-1 satellite fluxes present in the drift loss cone at L = 1.25. The presence of sufficient electron fluxes at L = 1.3 region in the SAA, and the similarity between the electron spectrum observed by the satellite experiments and that inferred in our balloon experiment, prompted us to investigate the possibility of the access of these electrons present at satellite altitudes into L = 1.13 regions during a mild storm. Interestingly, this prominent X ray flux event is associated with two succesive southward turnings of Bz component of the interplanetary magnetic field (IMF). Precipitation of essentially low-energy electrons below 150 keV occurred at the first northward reversal of IMF Bz and after the latter northward reversal higher energy electrons (> 150 keV) also precipitated. We suggest the diffusion of particles from higher L regions into flux tubes connected to the SAA region, due to electric field fluctuations associated with succession of substorms, in a process similar to the “enhanced radial diffusion” proposed by Lyons and Schulz [1989]. To compare or to relate the inferred fluxes from the balloon experiment with the satellite measurements and for a better understanding of the precipitation of electrons during magnetic disturbances, it is necessary to have additional experimental investigations in the SAA.

Surface ozone study in Campinas, Sao Paulo, Brazil

Abstract The first results of the surface ozone study in Campinas, Sao Paulo state, Brazil, are presented. During the local winter (dry season) the photochemical ozone production is found to be a regular process with the afternoon ozone mixing ratio maximum ranging from 10 to 15 ppbv during totally cloudy days to 40–60 ppbv during clear sky weather. Several high-value ozone episodes with ozone mixing ratios from 80 to 140 ppbv have been registered. At the beginning of the wet season the ozone concentration in Campinas did not decrease significantly as in the Amazonia forest region, but diurnal variations became more complicated with sharp dropouts during the days with rainfall and other fast changes of meteorological conditions. The fast irregular pulsations of ozone concentration with periods from the first tens of seconds to tens of minutes have been registered. Possible explanations of the nature of pulsations are briefly discussed. Photochemical ozone production by urban plumes of Campinas or Sao Paulo is named as a first possible source of the elevated ozone concentration and a local biomass burning is suggested as an alternative or an additional source.

On positron radiation belt in the Earth's magnetosphere

The ratio of positron/electron fluxes originated in nuclear spallation reactions in the Earths magnetosphere is considered. It is supposed that positrons as well as electrons are produced in the decay of charged pions (p±® m± ®e±) born in nuclear collisions of trapped relativistic inner zone protons with the residual atmosphere. These positrons and electrons are captured in the magnetosphere and create positron and electron radiation belts of nuclear origin. The positron/electron trapped magnetospheric fluxes formed with this mechanism are simulated and the resulting computed e+/e- flux ratio » 4 appears in agreement with the recent observations. This ratio is significantly different from the ratio »1 obtained from the primary cosmic ray source through the same mechanism.

About the origin of high energy electrons in the inner radiation belt

Abstract A large flux of > 100 MeV electrons were registered in the inner radiation belt on low-altitude satellites. The origin of that flux is discussed. It appears that slow radial diffusion ( D o = 10 −13 1/s) gives a low probability for penetration of these electrons to small L from the boundary of magnetosphere because of synchrotron radiation energy losses. It is found that they can enter to the inner belt region without such losses after great magnetic storms when high speed radial diffusion sometimes takes place. Two great storms on 8–9 Feb.] 986 and 24 March 1991 are examples when one can directly observe a penetration of energetic electron fluxes into magnetosphere. The assumption about their Jovian origin is discussed.

The trapped He flux dynamics observed on the OHZORA satellite during 1984–1987

The results of observations of spatial distribution and dynamics of trapped He fluxes with the energy 3.2-9.2 MeV/nuc obtained by low altitude Japanese OHZORA satellite are reported. Transient trapped He fluxes associated with solar and magnetospheric activity were observed at low altitudes in the region of L=2.0-3.0. Possible sources of the fluxes including remnants of solar particle population trapped during substorms, acceleration of hot plasma from the outer magnetosphere, and pitch-angle scattering from the top of the magnetic field line are discussed.

Sources of inner radiation zone energetic helium ions: Cross-field transport versus in-situ nuclear reactions

Radial transport theory for inner radiation zone MeV He ions has been extended by combining radial diffusive transport, losses due to Coulomb friction and charge exchange reaction with local generation of 3He and 4He ions due to nuclear reactions taking place on the inner edge of the inner radiation zone. From interactions between high energy trapped protons and upper atmospheric constituents we have included a nuclear reaction yield helium flux source that was numerically derived from a nuclear reaction model originally developed at the Institute of Nuclear Researches of Moscow, Russia and implemented in the computer system at the University of Campinas, Brazil. Magnetospheric transport computations have been made covering the L-shell range L=1.0 to 1.6 and the resulting MeV He ion flux distributions show a strong influence of the local nuclear source mechanism on the inner zone energetic He ion content.