Plasma bubble zonal velocity variations with solar activity in the Brazilian region

Abstract. A statistical study of the zonal drift velocities of the ionospheric plasma bubbles using experimental airglow data acquired at the low-latitude station Cachoeira Paulista (Geogr. 22.5° S, 45° W, dip angle 28° S) during the period of October to March, between 1980 and 1994, is presented here. This study is based on 109 nights of zonal plasma bubble velocity estimations as determined from bubbles signatures on the OI 630nm scanning photometer airglow data. The zonal velocity magnitudes of the plasma bubbles are investigated with respect to solar activity and local time. It is verified that these velocities tend to increase with the solar EUV flux, using the solar 10.7-cm radio flux as a proxy (F10.7). These velocities are seen to be larger during the solar maximum activity period than in the solar minimum period. As to the local time variation, they are seen to peak before midnight, in the 20:30-22:30 LT time frame, depending on the season. The all-data plot based on the 109 nights of airglow experiments shows that the plasma bubble mean zonal drift velocities tend to decrease with local time, but they peak at 22:25 LT, where the velocity magnitude reaches 127.4ms^-1. The zonal drift variations with local time and solar flux are shown in Figs. 1 and 2, respectively.