The longitudinal variability of equatorial electrojet and vertical drift velocity in the African and American sectors

Abstract

Abstract. While the formation of equatorial electrojet (EEJ) and its temporal variation is believed to be fairly well understood, the longitudinal variability at all local times is still unknown. This paper presents a case and statistical study of the longitudinal variability of dayside EEJ for all local times using ground-based observations. We found EEJ is stronger in the west American sector and decreases from west to east longitudinal sectors. We also confirm the presence of significant longitudinal difference in the dusk sector pre-reversal drift, using the ion velocity meter (IVM) instrument onboard the C/NOFS satellite, with stronger pre-reversal drift in the west American sector compared to the African sector. Previous satellite observations have shown that the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This study's results raises the question if the vertical drift, which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector -why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?

Statistical analysis of the correlation between the equatorial electrojet and the occurrence of the equatorial ionisation anomaly over the East African sector

“…To obtain the EEJ ( H ), the H S values calculated at ETHI were subtracted from those of the corresponding days that were calculated at AAE. Most studies on the EEJ report the peak of the diurnal EEJ around 12:00 LT (Gouin, 1962;Venkatesh et al, 2015;Yizengaw et al, 2014;Subhadra Devi and Unnikrishnan, 2014). In line with this information, the daytime EEJ strength for each day in this study was represented by the mean of the EEJ during the period 10:00-13:00 LT, when the peak of the daytime EEJ is expected to occur.…”

“…The same magnetometers have been used in several studies to determine the EEJ over the East African sector (e.g. Yizengaw et al, 2014Yizengaw et al, , 2010Olwendo et al, 2015). In Fig.…”

“…1, the dotted line represents the magnetic equator, while the dashed line represents the southern crest of the EIA. More details about data sites used in this study are provided in (Yizengaw et al, 2014). For each day, values of H measured at a particular station during 23:00-23:59 LT were averaged to give the H B value for that day.…”

“…Their results showed experimental evidence of how EEJ strength, which is a proxy of E × B drift, mostly controls plasma transportation over low latitudes. Usually, low values of E × B drifts result in poor formation of the EIA (Yizengaw et al, 2014;Olwendo et al, 2015).…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Therefore, the difference in H between the two stations contains only the EEJ effect. Because of the simplicity, the technique is widely used for studies of the equatorial electrojet (e.g., Anderson 2011;Yizengaw et al 2014). The true advantage of this technique is not the separation of Sq but the separation of magnetospheric contributions.…”