author = "Abdu, Mangalathayil Ali and Batista, Inez Staciarini and 
                         Muralikrishna, Polinaya and Sobral, Jos{\'e} Humberto Andrade",
                title = "Long term trends in sporadic E layers and electric fields over 
                         Fortaleza, Brazil",
              journal = "Geophysical Research Letters",
                 year = "1996",
               volume = "23",
               number = "7",
                pages = "757--760",
                month = "Apr.",
             keywords = "AERONOMIA, Fortaleza (Estado), camada E espor{\'a}dica, campos 
                         el{\'e}tricos, ionosfera terrestre, sporadic E layer.",
             abstract = "Long term trends in the sporadic E-layer occurrences and 
                         associated electric fields over the equatorial station, Fortaleza 
                         are analysed using 16 years (1975-1990) of ionosonde data. The 
                         secular drift of the magnetic equator and hence that of the 
                         equatorial electrojet current (EEJ) to northward of Fortaleza has 
                         resulted in marked long term changes in the occurrence 
                         characteristics of the different types of Es layers: the q-type 
                         (arising from electrojet instability processes) and the 1, f, c 
                         and h types (resulting from wind/wind shear mechanisms). 
                         Systematic decrease in the occurrence rates of the q-type Es, 
                         accompanied with increases in the remaining types of Es, was 
                         registered from 1975 to 1990, during which period the magnetic 
                         equator drifted to north of Fortaleza by 400km. The long term 
                         trend manifests competing roles of the equatorial electric field 
                         and wind systems, in the generation of the different types of Es 
                         layers as a function of the distance from the electrocjet center. 
                         The F-layer dynamo electric field is seen to exercise strong 
                         control of Es layer formation near sunset. Solar cycle variations, 
                         represented by the F10.7cm flux, seems to be present in electrojet 
                         intensity and the lower thermospheric wind system.",
                 issn = "0094-8276",
                label = "9357",
           targetfile = "8378.pdf",
        urlaccessdate = "15 jan. 2021"