author = "Sahai, Yogeshwar and Bittencourt, Jose Agusto and Sobral, Jose 
                         Humberto Andrade and Fagundes, Paulo Roberto and Takahashi, 
                title = "Observations of ionospheric plasma depletions using OI 630.0 nm 
                         nightglow imaging",
              journal = "Revista de la Academia de Ciencias de Bolivia",
                 year = "1996",
               volume = "14",
               number = "1",
                pages = "15--28",
                         LUMINESCENCIA, IMAGEAMENTO OTICO, EMISSAO OI 630.0 NM.",
             abstract = "Ionospheric plasma irregularities associated with nighttime 
                         equatorial spread-F phenomena have been the subject of intensive 
                         experimental and theoretical investigations during recent years. 
                         Large scale plasma depletions, referred to as transequatorial 
                         bubbles or plumes, continue to attract considerable attention. The 
                         studies of ionosphere plasma irregularities assume great 
                         importance, because the irregularities degrade the radio wave 
                         signals passing through the region and, therefore, have 
                         considerable influence on the ionospheric/trans-ionospheric radio 
                         wave communications. The F-region nightglow emissions arising from 
                         ionospheric recombination processes can be used to remotely 
                         observe the dynamics of transequatorial ionospheric plasma bubbles 
                         and smaller scale plasma irregularities. In a collaborative 
                         project between the Center for Space Physics, Boston University, 
                         USA- and the National Institute for Space Research (INPE), Brazil, 
                         an all-sky imaging system was put in operation at Cachoeira 
                         Paulista (22.7 degree S, 45.0 degree W, dip latitude 15.8 degree 
                         S), in March 1987. This wide angle imaging technique provides an 
                         unique capability of permiting observations over regions covering 
                         several million square kilometers from a single observing station. 
                         Also, regular measurements of several nightglow emissions and 
                         ionospheric sounding are carried out at Cachoeira Paulista and 
                         Fortaleza (3.9 degree S, 38.4 degree W, dip latitude 3.7 degree 
                         S). A VHF electronic polarimeter was in operation at Cachoeira 
                         Paulista. This clustering of observational facilities in the 
                         Brazilian sector provided coincident and complementary 
                         observations of various upper atmospheric parameters. In this 
                         paper we present and discuss some features of the 01630.0 nm 
                         emission all-sky imaging observations carried out during the 
                         period 1987-1989. The transequatorial ionospheric plasma bubbles 
                         manifest in all-sky optical imaging observations as nearly 
                         north-south aligned intensity-depleted regions. The observed 
                         seasonal variation of the airglow depletions shows a maximum 
                         during the summer months and virtually no airglow depletions 
                         during the winter months. The case studies presented show 
                         different forms of generation and development phases of airglow 
                         depletions during the course of a night. The all-sky images also 
                         permitted the determination of the altitude-latitude extent of the 
                         plasma depleted regions and some results are presented. It has 
                         been observed that the attitudes reached by the plasma depleted 
                         flux tubes over the magnetic equator in the Brazilian sector-often 
                         exceed 2500 km.",
                label = "8766",
           targetfile = "7406.pdf",
        urlaccessdate = "24 jan. 2021"