@Article{FagundesSaBaAbBiTa:1999:ObDaVa,
               author = "Fagundes, P. R. and Sahai, Yogeshwar and Batista, Inez Staciarini 
                         and Abdu, Mangalathyil Ali and Bittencourt, Jos{\'e} Augusto and 
                         Takahasho, Hisao",
                title = "Observation of day-to-day variability in precursor signatures to 
                         equatorial F-region plasma depletions",
              journal = "Annales Geophysicae",
                 year = "1999",
               volume = "17",
               number = "8",
                pages = "1053--1063",
                month = "Aug.",
             keywords = "AERONOMIA, composi{\c{c}}{\~a}o da atmosfera, 
                         aeroluminesc{\^e}ncia, equador magn{\'e}tico, regi{\~a}o F, 
                         irregularidades, bolhas de plasma, atmospheric composition, 
                         airglow, auroras, magnetic equator, F region, irregularities, 
                         plasma bubbles.",
             abstract = "In December 1995, a campaign was carried out to study the 
                         day-to-day variability in precursor signatures to large-scale 
                         ionospheric F-region plasma irregularities, using optical 
                         diagnostic techniques, near the magnetic equator in the Brazilian 
                         sector. Three instruments were operated simultaneously: (a) an 
                         all-sky (180 degrees field of view) imaging system for observing 
                         the OI 630 nm nightglow emission at Alcantara (2.5 degrees S, 44.4 
                         degrees W); (b) a digisonde (256-Lowell) at Sao Luis (2.6 degrees 
                         S, 44.2 degrees W); and (c) a multi-channel tilting filter-type 
                         zenith photometer for observing the OI 630 nm and mesospheric 
                         nightglow emissions at Fortaleza (3.9 degrees S, 38.4 degrees W). 
                         During the period December 14-18, 1995 (summer in the southern 
                         hemisphere) a good sequence of the OI 630 nm imaging observations 
                         on five consecutive nights were obtained, which are presented and 
                         discussed in this study. The observing period was geomagnetically 
                         quiet to moderate (Kp = 0+ to 5+; Dst = 18 nT to -37 nT). On four 
                         nights, out of the five observation nights, the OI 630 nm imaging 
                         pictures showed formations of transequatorial north-south aligned 
                         intensity depletions, which are the optical signatures of 
                         large-scale ionospheric F-region plasma bubbles. However, 
                         considerable day-to-day variability in the onset and development 
                         of the plasma depleted bands was observed. On one of the nights it 
                         appears that the rapid uplifting of the F-layer in the postsunset 
                         period, in conjunction with gravity wave activity at mesospheric 
                         heights, resulted in generation of very strong plasma bubble 
                         irregularities. One of the nights showed an unusual formation of 
                         north-south depleted band in the western sector of the imaging 
                         system field of view, but the structure did not show any ard 
                         movement, which is a normal characteristic of plasma bubbles. This 
                         type of irregularity structure, which probably can be observed 
                         only by wide-angle imaging system, needs more investigations for a 
                         better understanding of its behaviour.",
                 issn = "0992-7689",
                label = "9672",
             language = "en",
        urlaccessdate = "12 maio 2024"
}