author = "Cueva, R. Y. C. and Rodrigues, F. S. and Paula, Eurico Rodrigues 
                         de and Tsunoda, R. T. and Groves, K. M. and Raulin, J. P.",
          affiliation = "{Universidade Presbiteriana Mackenzie} and {University of Texas} 
                         and {Instituto Nacional de Pesquisas Espaciais (INPE)} and {SRI 
                         International} and {Boston College} and {Universidade 
                         Presbiteriana Mackenzie}",
                title = "Spread F echoes variability along solar flux and seasonality 
                         conditions over the 50- MHz radar on Christmas Island",
                 year = "2015",
         organization = "International Congress of the Brazilian Geophysical Society, 14.",
             abstract = "Perturbations in the amplitude (or phase) of radio signals are 
                         caused by irregularities in the ionospheric electron density. 
                         Ionospheric structures can disrupt the propagation of radio waves, 
                         and are commonly observed, for instance, by ionospheric vertical 
                         radio sounders (ionosondes). For historical reasons, the 
                         signatures of ionospheric irregularities in different types 
                         observations (optical, radio, in-stu) are referred to as 
                         equatorial spread F (ESF). Previous studies show that the 
                         occurrence rate can be greatly affected by solar and magnetic 
                         conditions. Observations during the period of 2003 to 2012 of 
                         nighttime echoes made from the 50-MHz radar on Christmas Island 
                         (2.0o N, 157.4o W) have revealed time and altitude pattern 
                         distribution along the descending phase of solar cycle 23 and the 
                         recent extended solar minimum phase. We present the study of 
                         spread F echoes as a function of solar flux conditions and 
                         seasonality in order to quantify their variability. Under higher 
                         solar flux conditions, echoes reach higher altitudes but decay 
                         earlier. Only during solar minimum conditions the echoes exist 
                         throughout the whole night, since the post\‐ reversal 
                         anti\‐ zonal background electric field is weaker. Thus, 
                         irregularities during solar maximum will be dominated by dynamics 
                         near the time of the PRE. Since the population of irregularities 
                         during solar minimum exists throughout the whole night, 
                         post\‐ reversal ionospheric conditions may play a role in 
                         the morphology of plasma irregularities, especially with the 
                         coincidentally weaker PRE during solar minimum. Peak time 
                         occurrence of echoes along the current period show a well defined 
                         pattern, meanwhile the peak altitude occurrence of echoes show a 
                         slight regular pattern.",
  conference-location = "Rio de Janeiro, RJ",
      conference-year = "3-6 Aug.",
        urlaccessdate = "24 nov. 2020"