author = "Abdu, Mangalathayil Ali and Souza, Jonas Rodrigues de and Kherani, 
                         Esfhan Alam and Batista, Inez Staciarini and MacDougall, J. W. and 
                         Sobral, Jos{\'e} Humberto Andrade",
          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 {University of Western Ontario} and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)}",
                title = "Wave structure and polarization electric field development in the 
                         bottomside F layer leading to postsunset equatorial spread F",
              journal = "Journal of Geophysical Research A: Space Physics",
                 year = "2015",
               volume = "120",
               number = "8",
                pages = "6930--6910",
                month = "Aug.",
             keywords = "electric field, equatorial spread F, gravity waves, large-scale 
                         wave structure, PRE vertical drift, prereversal vertical drift.",
             abstract = "In this paper we present the results of a study on the 
                         characteristics of large-scale wave structure in the equatorial 
                         ionospheric F region that serve as precursor to postsunset 
                         development of the spread F/plasma bubble irregularities. The 
                         study is based on analysis of Digisonde data from three equatorial 
                         sites in Brazil (Fortaleza, Sao Luis, and Cachimbo) for a period 
                         of about 2 months at a medium solar activity phase. 
                         Small-amplitude oscillations in the F layer heights, extracted at 
                         a number of plasma frequencies, present characteristics as them 
                         being generated from upward propagating gravity waves. They 
                         represent wave structures in polarization electric field having 
                         zonal scale of a few hundred kilometers. Their amplitudes in the 
                         afternoon hours undergo amplification toward evening, leading to 
                         postsunset development of equatorial spread F/plasma bubble 
                         irregularities, on a statistical basis. On the days of their 
                         larger amplitudes they appear to occur in phase coherence on all 
                         days, and correspondingly, the evening prereversal vertical drift 
                         velocities are larger than on days of the smaller amplitudes of 
                         the wave structure that appear at random phase on the different 
                         days. The sustenance of these precursor wave structures is 
                         supported by the relatively large ratio (approaching unity) of the 
                         F region-to-total field line-integrated Pedersen conductivities as 
                         calculated using the Sheffield University Plasmasphere-Ionosphere 
                         Model simulation of the low-latitude ionosphere. The significant 
                         amplification in the wave structure toward sunset and the {"}phase 
                         coherent{"} nature of their occurrences on different days are 
                         explained tentatively on the basis of the spatial resonance 
                  doi = "10.1002/2015JA021235",
                  url = "http://dx.doi.org/10.1002/2015JA021235",
                 issn = "2169-9402",
             language = "en",
           targetfile = "Abdu et al_2015Wave structures-1.pdf",
        urlaccessdate = "26 jan. 2021"