Browsing by Author "Obrou, O. K."

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    Equatorial plasma bubbles and L-band scintillations in Africa during solar minimum
    (European Geosciences Union (EGU), 2012-04-16) Paznukhov, V. V.; Carrano, C. S.; Doherty, P. H.; Groves, K. M.; Caton, R. G.; Valladares, C. E.; Seemala, G. K.; Bridgwood, C. T.; Adeniyi, J.; Amaeshi, L. L. N.; Damtie, B.; D’Ujanga Mutonyi, F.; Ndeda, J. O. H.; Baki, P.; Obrou, O. K.; Okere, B.; Tsidu, G. M.
    We report on the longitudinal, local time and seasonal occurrence of equatorial plasma bubbles (EPBs) and L band (GPS) scintillations over equatorial Africa. The measurements were made in 2010, as a first step toward establishing the climatology of ionospheric irregularities over Africa. The scintillation intensity is obtained by measuring the standard deviation of normalized GPS signal power. The EPBs are detected using an automated technique, where spectral analysis is used to extract and identify EPB events from the GPS TEC measurements. Overall, the observed seasonal climatology of the EPBs as well as GPS scintillations in equatorial Africa is adequately explained by geometric arguments, i.e., by the alignment of the solar terminator and local geomagnetic field, or STBA hypothesis (Tsunoda, 1985, 2010a). While plasma bubbles and scintillations are primarily observed during equinoctial periods, there are longitudinal differences in their seasonal occurrence statistics. The Atlantic sector has the most intense, longest lasting, and highest scintillation occurrence rate in-season. There is also a pronounced increase in the EPB occurrence rate during the June solstice moving west to east. In Africa, the seasonal occurrence shifts towards boreal summer solstice, with fewer occurrences and shorter durations in equinox seasons. Our results also suggest that the occurrence of plasma bubbles and GPS scintillations over Africa are well correlated, with scintillation intensity depending on depletion depth. A question remains about the possible physical mechanisms responsible for the difference in the occurrence phenomenology of EPBs and GPS scintillations between different regions in equatorial Africa.
    Palabras clave:IonosphereEquatorial ionosphereSpace and satellite communication
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    Response of the equatorial ionosphere to the geomagnetic DP 2 current system
    (American Geophysical Union, 2016-07-12) Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Magoun, M.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O. K.; Bamba, Z.; Paula, E. R. de
    The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground‐based multiinstrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP 2 current system. The quasiperiodic DP 2 current system, which fluctuates coherently with fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high‐latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.
    Palabras clave:DP 2 currentEquatorial electrodynamicsAtmospheric electricity