Observations of equatorial F region plasma bubbles using simultaneous OI 777.4 nm and OI 630.0 nm imaging:: New results

Simultaneous observations of the OI 630.0 nm and OI 777.4 nm nightglow emissions using all-sky imaging systems and ionospheric radio sounding using a Canadian Advanced Digital Ionosonde (CADI) digisonde have been recently carried out at Sao Jose dos Campos (23.21degreesS, 45.86degreesW), Brazil. The all-sky imaging systems use novel CCD devices, with high quantum efficiency and which provide an exceptional capacity for quantitative measurement of faint- and low-contrast emissions. On October 23-24, 2000 (high solar activity), the presence of large-scale F region plasma irregularities (plasma bubbles) was observed using both techniques (i.e., optical and radio). The high-resolution images, recorded using the OI 777.4 nm nightglow emission, show a new striated or ray-like pattern, which has not been detected before. These OI 777.4 nm optical observations show for the first time, in great detail, the field-aligned ionospheric plasma bubble structures, in contrast with the OI 630.0 nm images, which show a diffuse image of the bubbles. The optical signatures of the OI 777.4 nm emission are more closely related to the actual ionospheric bubble structure, owing to its prompt emission and dependence only on the electron density, with no F layer height dependence. On the other hand, the OI 630.0 rim emission comes from the bottomside of the F layer with a strong F layer height dependence and shows blurred images due to its 110-s lifetime. An additional advantage of using the OI 777.4 nm emission for ionospheric irregularity studies is that the plasma bubbles can be observed earlier on the OI 777.4 nm images than on the OI 630.0 nm images (by similar to 15 min).