Observações de bolhas de plasma ionosféricas na região equatorial brasileira.

Abstract

Observations of OI 630.0 nm (OI6300) nightglow emission was carried out over a period of almost eleven years, spanning September 2000 to December 2010 over São João do Cariri (7.4oS; 36.5oW), Brazil using an all-sky imager (ASI) in order to observe equatorial plasma bubble (EPB) in the bottomside of ionospheric F region. In total, there were 1107 nights of observation, and out of these, about 648, representing 58.5%, showed the occurrence of EPBs. Certain characteristics such as onset, disappearance and other visible characteristics of plasma bubbles, such as bifurcation, multiple and single structure were observed in the monochromatic OI6300 airglow images. The large size of the database made it possible to analyze these characteristics during almost an entire solar cycle period. It showed from the analysis that from September to April (spring-summer) had the highest occurrence rate of 69.3% and the least occurrence rate of 30.6% was from May to August (winter). The characteristics, except for single, mentioned above have similar seasonal patterns. However, for the months of May, June and July we observed no bifurcations. Single plasma bubbles were the least observed in the analysis and their occurrence is rather random (show no seasonal pattern) with the highest number of 3, occurring in May and 1 in January, March and December for the 11 years of study. Many of the bubbles that occurred during the winter period started late in the evening as opposed to the spring and summer periods which started earlier in the evening. However, the occurrence rate is greater around period of high solar activity (2000-2005) (about 57.3%) compared to period of low solar activity (2006-2010) (42.7%) even though the seasonal variation is similar for those periods. Analysis of the start time produced oscillations of 3-4 days, 5-6 days and greater than 7 days periods, which show clear day-to-day variability in the start time. These periods may have resulted from the effects of planetary waves in the ionosphere, modulating the pre-reversal enhancement. The pre-reversal, which is a necessary condition for Rayleigh-Taylor instability, which is the main mechanism of generation of the equatorial plasma bubble.