Ionospheric plasma bubble climatology over Brazil based on 22 years (1977-1998) of 630 nm airglow observations

The frequency of occurrence of the large-scale ionospheric plasma depletions, or plasma bubbles, over Cachoeira Paulista-CP (45degreesW, 33degreesS, 28degreesS dip), with solar activity, season, and geomagnetic activity, during the period of 1977-1998, is studied here based on 934 days of scanning photometers and imagers data of the atomic oxygen 630 nm nocturnal airglow. The bubble occurrence for the entire period of study shows maximum rate of 86% in January and 11% in May. The seasonal pattern of the bubble occurrence shows up as broad a maximum and a minimum centered around summer and winter months, respectively. While during the high-solar activity the maximum extends from September to April, for the low-activity period it extends from October to March. The average sunspot number for the solar maximum (minimum) for the data of this work is 129.9 (33.1). Significant increase of bubble occurrence (by similar to80%) from low to high solar activity levels is found to occur in the present analysis only during the equinoctial months of March-April and September-October. The post-sunset plasma bubble occurrence over Cachoeira Paulista is found to decrease with increase of K-p that precedes the sunset by > 4 h, suggesting the role of disturbance dynamo electric field to inhibit its development. Increase of K-p during sunset hours can increase the bubble occurrence as a possible effect of prompt penetration electric field. These results are presented and discussed in this paper. (C) 2002 Elsevier Science Ltd. All rights reserved.