Emissão, propagação e amplificação da radiação quilométrica das auroras nas subcavidades aurorais

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

2001

RESUMO

The present work investigates the propagation and amplification of electromagnetic waves in a plasma localized in the vicinity of the geomagnetic poles, at heights not much greater than three times the Earth s radius. The phenomena studied is known as the Aurorai Kilometric Radiation (AKR), the strongest of the various types of emission that can occur as a consequence of the interaction of the solar wind and the terrestrial magnetosphere. Initially some of the main known characteristics of this emission are discussed, including a review of the literature on the observational features of the phenomena. The electron cyclotron maser mechanism is then discussed as a possible generator mechanism for the AKR. This mechanism is then utilized in order to study the propagation and amplification of the Aurorai Kilometric Radiation, the physical parameters necessary for this study being obtained from a physical model based in the work of Chiu &Schultz (1978), which approximately reproduces the plasma conditions in the source region. The model includes the gradients perpendicular to the ambient magnetic field, with small scale variations of the density, called auroral subcavities. The componente of the plasma dielectric tensor are calculated for one distribution which consists in a summation of a Maxwellian, which describes cold electrons, and a relativistic DGH distribution for the energetic loss-cone electrons, being used the locally homogeneous approximation. A ray-tracing study is done using the geometrical optics equations, and at each point along the wave trajectory the spectral emissivity is calculated. By means of the transfer equation, the wave amplification factor is obtained for as long as the wave propagates in the source region. It is verified that the inclusion of the emissivity of the medium in the ray tracing calculation enhances the amplification factor. However, the increase obtained is not sufficient to expiam the amplification leveis currently observed. On the other hand, it is concluded that the inclusion of small scale variations (in the direction perpendicular to the magnetic field) in the density and other plasma parameters in the source region, may be an important factor in the explanation of the observed amplification leveis.

ASSUNTO(S)

propagacao de ondas eletromagneticas em plasmas auroras radiacao propriedades dieletricas dos gases campos magneticos densidade otica geometrica tensores

ACESSO AO ARTIGO

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