author = "Onohara, Amelia Naomi and Batista, Inez Staciarini and Batista, 
                         Paulo Prado",
          affiliation = "{Ag{\^e}ncia Espacial Brasileira (AEB)} and {Instituto Nacional 
                         de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "Wavenumber-4 structures observed in the low-latitude ionosphere 
                         during low and high solar activity periods using FORMOSAT/COSMIC 
              journal = "Annales Geophysicae",
                 year = "2018",
               volume = "36",
               number = "2",
                pages = "459--471",
                month = "Mar.",
             keywords = "Ionosphere (equatorial ionosphere).",
             abstract = "The main purpose of this study is to investigate the four-peak 
                         structure observed in the low-latitude equatorial ionosphere by 
                         the FORMOSAT/COSMIC satellites. Longitudinal distributions of NmF2 
                         (the density of the F layer peak) and hmF2 (ionospheric F2-layer 
                         peak height) averages, obtained around September equinox periods 
                         from 2007 to 2015, were submitted to a bi-spectral Fourier 
                         analysis in order to obtain the amplitudes and phases of the main 
                         waves. The four-peak structure in the equatorial and low-latitude 
                         ionosphere was present in both low and high solar activity 
                         periods. This kind of structure possibly has tropospheric origins 
                         related to the tidal waves propagating from below that modulate 
                         the E-region dynamo, mainly the eastward nonmigrating diurnal tide 
                         with wavenumber 3 (DE3, E for eastward). This wave when combined 
                         with the migrating diurnal tide (DW1, W for westward) presents a 
                         wavenumber4 (wave-4) structure under a synoptic view. Electron 
                         densities observed during 2008 and 2013 September equinoxes 
                         revealed that the wave-4 structures became more prominent around 
                         or above the F-region altitude peak ( \∼ 300350 km). The 
                         four-peak structure remains up to higher ionosphere altitudes 
                         (\∼ 800 km). Spectral analysis showed DE3 and SPW4 
                         (stationary planetary wave with wavenumber 4) signatures at these 
                         altitudes. We found that a combination of DE3 and SPW4 with 
                         migrating tides is able to reproduce the wave-4 pattern in most of 
                         the ionospheric parameters. For the first time a study using wave 
                         variations in ionospheric observations for different altitude 
                         intervals and solar cycle was done. The conclusion is that the 
                         wave-4 structure observed at high altitudes in ionosphere is 
                         related to effects of the E-region dynamo combined with transport 
                         effects in the F region.",
                  doi = "10.5194/angeo-36-459-2018",
                  url = "http://dx.doi.org/10.5194/angeo-36-459-2018",
                 issn = "0992-7689",
             language = "en",
           targetfile = "onohrara_wavenumber.pdf",
        urlaccessdate = "11 maio 2021"