author = "Bonelli, E. and Cueva, R. Y. L. C. and Paula, Eurico Rodrigues 
          affiliation = "{Universidade Federal do Rio Grande do Norte} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "GPS scintillation at two low magnetic latitude stations in Brazil 
                         during the 2008-2009 prolonged solar minimum",
            booktitle = "Proceedings...",
                 year = "2009",
         organization = "Iaga, 2009.",
             keywords = "ionospheric scintillation, ionospheric irregularities, gps 
             abstract = "GPS scintillations are caused by irregularities in the ionospheric 
                         plasma density. At low magnetic latitudes, irregularities occur 
                         mostly just after sunset, due to an increase in the eastward 
                         electric field, the pre-reversal enhancement electric field, a 
                         phenomenon due to the ionospheric dynamo. This intense eastward 
                         electric field drives the plasma up fast and usually causes the 
                         formation of plasma density irregularities. These plasma 
                         irregularities cause ionospheric scintillations, which are 
                         fluctuations in radio signals received from artificial satellites 
                         or natural sources like stars and galaxies. Scintillations are 
                         intense during periods of maximum solar activity. Now, however, 
                         they are very weak, especially in GPS signals, since the Sun has 
                         stationed around a minimum of activity. It is believed that plasma 
                         bubbles originate at the magnetic equator and then propagate 
                         through higher latitudes by moving up and diffusing along magnetic 
                         field lines. For this reason, only very low latitudes show 
                         scintillations, now. We have chosen two low latitude stations, 
                         almost aligned with the same magnetic meridian, S{\~a}o Luis (dip 
                         -4.5, at 300 km) and Natal (dip -28, at 300 km) both with a -20 
                         declination. Scintillations were recorded at both stations at the 
                         rate of 50 samples per second per satellite, for the period of 
                         September/2008 through March/2009. To compare the scintillations 
                         at both stations the S4 index is averaged first hourly, for all 
                         satellites, and then for the whole night for all satellites. A 
                         surprising result is that it is not clear from the data that the 
                         irregularities are being produced at the lower latitude station 
                         and then moving to the higher latitude station. Some results show 
                         an increase of scintillations in Natal, which does not occur in 
                         S{\~a}o Luis. These results are discussed in terms of production 
                         of irregularities at Natal, at S{\~a}o Luis, and at other sites, 
                         estwards, and then moving west to these stations.",
  conference-location = "Sopron, Hungary",
      conference-year = "23-30 Aug.",
             language = "en",
        urlaccessdate = "24 jan. 2021"