Abstract
Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.
Highlights
The vertical E × B drift driven by the zonal electric field and horizontal northward magnetic field significantly affects the structure and dynamics of the equatorial F-region ionosphere
Considering the results reported by Stolle et al (2008), the evening counter electrojet (CEJ) modifies the plasma density distribution around and inside the equatorial ionization anomaly (EIA) crests around sunset, since the evening CEJ that makes the pre-sunset integrated EEJ ground strength (IEEJ) negative already starts in the afternoon
The pre-reversal enhancement (PRE) strengths and equatorial spread-F (ESF) onsets are found to be suppressed when the presunset IEEJ is negative owing to the evening CEJ
Summary
The vertical E × B drift driven by the zonal electric field and horizontal northward magnetic field significantly affects the structure and dynamics of the equatorial F-region ionosphere. The vertical E × B drift is generally upward during the daytime and downward during the nighttime. The eastward electric field is mainly generated by the E-region dynamo. The dynamo electric field simultaneously drives a zonal current in the E-region. Such a current is intensified in the vicinity of the magnetic equator with the range of a few degrees and is called the equatorial electrojet (EEJ) (Chapman, 1951). EEJ causes large variations, typically several tens nT, in the geomagnetic field, and it has been extensively studied by analysing the ground-based magnetometer data (e.g., Doumouya et al, 1998)
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