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

P M Terra,J R Souza,H Takahashi,M A Abdu,J H A Sobral

doi:10.5194/angeo-22-3123-2004

Abstract

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.

Highlights

The low-latitude ionosphere bears the remarkable phenomena of plasma depletions, or bubbles, which consist of extended regions of depleted F-region plasma
The zonal drifts of the plasma bubbles result from the vertical polarization electric fields that are generated through complex interactions among the tidal winds, the geomagnetic field and the ionospheric plasma in the F-region
This work concerns the results of a statistical study of the zonal drift velocities of the plasma bubbles using scanning (±75◦ around zenith in the East-West direction) photometer airglow data acquired at the low-latitude station Cachoeira Paulista (22.5◦ S, 45◦ W, dip 28◦ S), based on 109 nights of experiments during the period of October to March, between 1980 and 1994

Summary

Introduction

The low-latitude ionosphere bears the remarkable phenomena of plasma depletions, or bubbles, which consist of extended regions of depleted F-region plasma. The zonal drifts of the plasma bubbles result from the vertical polarization electric fields that are generated through complex interactions among the tidal winds, the geomagnetic field and the ionospheric plasma in the F-region. Studies of the plasma bubble zonal drift velocities’ behavior have been carried out using several techniques, such as the OI 630 nm monitoring in low-latitude and equatorial localities using allsky imager and photometer systems (Sobral et al, 1985; Sobral and Abdu, 1990, 1991; Fejer et al, 1985; Basu et al, 1996; Valladares et al, 1996; Taylor et al, 1997; de Paula et al, 2002; Martinis et al, 2003; Pimenta et al, 2003)

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Conclusion