@Article{CandidoBaBeAbSoTa:2011:SpOcOv,
               author = "Candido, Cl{\'a}udia Maria Nicoli and Batista, Inez Starciarini 
                         and Becker-Guedes, F{\'a}bio and Abdu, Mangalahyil Ali and 
                         Sobral, Jos{\'e} Humberto de Andrade and Takashi, Hisao",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Instituto Nacional de Pesquisas Espaciais 
                         (INPE)}",
                title = "Spread F occurrence over a southern anomaly crest location in 
                         Brazil during June solstice of solar minimum activity",
              journal = "Journal of Applied Geophysics",
                 year = "2011",
               volume = "116",
                pages = "AO6316.",
                month = "Jun 24",
             keywords = "VERTICAL PLASMA DRIFTS, AMERICAN SECTOR, LOW LATITUDES, 
                         EQUATORIAL, REGION, IRREGULARITIES, DISTURBANCES, DEPLETIONS, 
                         SATELLITE, BUBBLES.",
             abstract = "We present a study of Spread F occurrence over a location under 
                         the southern crest of the equatorial ionization anomaly (Cachoeira 
                         Paulista 22.7 degrees S, 45.0 degrees W, mag. Lat.: 16 degrees S, 
                         dip angle: -32.3 degrees, Brazil) during the last solar cycle, 
                         which presented an extended solar minimum activity. After 
                         analyzing hundreds of ionograms obtained with a digital ionosonde 
                         DGS 256, between 2001 and 2010, we verified high Spread F 
                         occurrence around midnight-postmidnight during June solstice 
                         (Southern Hemisphere winter) with a peak occurrence between 2006 
                         and 2009, when the solar flux has reached very low values (<70 
                         SFU). At the Brazilian sector the occurrence of Spread F is known 
                         to be associated with equatorial plasma bubbles (EPBs) and is 
                         observed mainly between September and March. On the other hand, 
                         EPBs are rarely observed over Cachoeira Paulista (hereafter 
                         referred as CP) during June solstice because of the weak 
                         magnitudes of the equatorial electric field prereversal 
                         enhancement, an essential condition to the development of the 
                         large-scale irregularities at the equatorial region. Despite the 
                         rarity of EPBs, we observed several strong Spread F events 
                         occurring under low plasma densities conditions which can extend 
                         for several hours. We have found evidences that the Spread F 
                         events over CP during June solstices of low solar activity can be 
                         caused by ionospheric disturbances that are unrelated to 
                         equatorial processes. Finally we present a statistical analysis of 
                         the events and we suggest that traveling ionospheric disturbances 
                         could be one of the main sources of these nonequatorial Spread F 
                         events.",
                  doi = "10.1029/2010JA016374",
                  url = "http://dx.doi.org/10.1029/2010JA016374",
                 issn = "0926-9851",
             language = "en",
        urlaccessdate = "01 maio 2024"
}