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  • Artigo
    V.L.F. propagation across the geomagnetic anomaly during S.I.D.s
    Kaufmann P.; Schaal R.E.; Lopes W.; Arakaki L. (1967)
    A number of S.I.D.s (sudden ionospheric disturbances) has been selected and analysed, in order to find some compatibility with the general form of the theory of waveguide mode propagation in an Earth-ionosphere spherical waveguide having an upper boundary characterized by a conductivity parameter derived from an exponential model. The v.l.f. (very low frequency) transmissions were received at a site located near the center of the South Atlantic Geomagnetic Anomaly, all of them crossing the region of the equatorial electrojet-and the results show that the general formulation may be used if the daytime upper boundary is less than 65 km. On the other hand the peculiar physical conditions found in the upper atmosphere along such paths possibly have an important influence on its shape and on the considered waveguide configuration, and they must be considered for getting a better understanding of the S.I.D. effects. Further experiments are suggested, emphazising the need of a more accurate knowledge of the dependence of the ionospheric parameter L on frequency. © 1967.
  • Artigo
    Experimental results from measurements performed during the 12 November 1966 total solar eclipse with a 4.28-cm radio polarimeter
    Kaufmann P.; Matsuura O.T.; Dos Santos P.M. (1967)
    Radio observations of the Sun with a 4.28-cm radio polarimeter were performed during the 12 November 1966 total solar eclipse at a site located near the city of Bagé, in the extreme south of Brazil. The solar activity during that period is discussed, giving additional data for the eclipse measurements themselves. The difference between radio and optical contacts indicated that there is a significant radio emission at a height near 0.12 solar radii over the photosphere, and the basic residual flux due to the contribution of the ring during the totality was found to be 12.2% of the total flux. An important "radio spot" was present near the center of the solar disk, contributing almost alone to the observed basic left-handed circularly polarized component of solar radiation. During totality no important residual polarization was found and if it still existed it is neglectable. © 1967.
  • Artigo
    Some results obtained with v.l.f. atmospherics measurements at São Paulo, Brazil
    Kaufmann P.; Lopes W.; Schaal R.E. (1967)
    Analysis of 10 months of v.l.f. atmospherics noise level fluctuations during 1963 has been done. The measurements have been performed with rather simple equipment and some interesting results were obtained concerning daily variations as a function of solar zenithal angles, and a number of effects peculiar to sunrise and sunset are discussed. Emphasis is placed on an understandable confusion which arises when attempting to study v.l.f. propagation through the ionosphere from atmospherics activity, since a certain number of randomly occurring features are difficult to determine. © 1967.
  • Artigo
    The effect of a total solar eclipse on long path VLF transmission
    Kaufmann P.; Schaal R.E. (1968)
    The effects of the total solar eclipse of 12 November 1966 on VLF transmissions at 26·1 kHz transmitted from NPM, Hawaii, and received at São Paulo, are presented. The eclipse occurred during the sunrise transition period, making the data interpretation rather difficult. There was a clearly-marked change of phase, corresponding to a maximum delay of 12·3 sec. © 1968.