Ionospheric zonal velocities at conjugate points over Brazil during the COPEX campaign: Experimental observations and theoretical validations

Abstract

[1] We analyze in detail the zonal velocities of large-scale ionospheric plasma depletions over two conjugate stations inferred from OI 630 nm airglow all-sky images obtained during the Conjugate Point Equatorial Experiment (COPEX) campaign carried out in Brazil between October and November 2002. The conjugate stations were Boa Vista (BV) (geogr. 2.8N, 60.7W, dip angle 22.0°N) and Campo Grande (CG) (geogr. 20.5S, 54.7W, dip angle 22.32°S). Over Campo Grande, the zonal velocities were measured also by a system of spaced GPS scintillation receivers. The airglow zonal velocities at the conjugate sites were seen to agree very closely, except for a slightly increased velocity over CG which we attribute to the presence of the geomagnetic anomaly. The results show a high degree of alignment of the bubbles along the geomagnetic field lines during the bubble development phase and as the bubbles travel eastward, thereby suggesting that the neutral zonal wind effect in the zonal plasma motion is an integrated effect along the flux tube. The zonal velocities obtained from the GPS technique were always larger than those calculated by the airglow technique, which permitted observation of zonal plasma velocity shear between the altitudes of the airglow emitting layer and of the GPS scintillation. Theoretical ambient plasma zonal velocities calculated using the formulations by and Eccles (1998) are compared with the experimental results. Our results also reveal some degree of dependence of the zonal velocities on the solar flux (F10.7) and magnetic (Kp) indices during the COPEX period.

Low Latitude Ionospheric Electrodynamics

“…Measurements in the Brazilian equatorial region during the COPEX campaign showed larger nighttime eastward drifts observed with the GPS technique than inferred from airglow observations (Sobral et al 2009). Simultaneous observations with these two techniques also provided information on the early night shear in the zonal plasma drift between the heights of the airglow and the GPS scintillation layers.…”

“…Ground-based optical and spaced GPS observations have extensively been used to measure nighttime zonal drifts of equatorial plasma depletions over Brazil (e.g., Sobral et al 1999Sobral et al , 2009Terra et al 2004). Measurements in the Brazilian equatorial region during the COPEX campaign showed larger nighttime eastward drifts observed with the GPS technique than inferred from airglow observations (Sobral et al 2009).…”

Zonal velocity of the equatorial plasma bubbles over Kolhapur, India

“…This aspect is also noted by few other investigators. Sobral et al (2009) reported that a tendency of the zonal velocities of EPBs to increase almost linearly with increasing solar flux units. The thermospheric zonal wind is responsible for the motion of EPBs.…”

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

“…(2013), and the authors observed a slower rate of increase in F10.7 in comparison to the increase in the EUV flux for high solar flux values, which might explain the nonlinearity feature depicted here in the plot of V zonal versus the F10.7 index. The solar flux effects on irregularity zonal velocities have also been studied by Sobral et al (2009) based on the formulations presented by Haerendel et al (1992) and Eccles (1998). They discussed the fact that around solar maximum years the magnitude of the thermospheric zonal wind velocities tends to be larger owing to an enhanced solar thermal tide.…”