Superrotation of the ionosphere and quiet time zonal ion drifts at low and middle latitudes observed by Republic of China Satellite-1 (ROCSAT-1)

Abstract

[1] Local-time variations of zonal drifts at different latitudes, longitudes, and seasons are investigated using ion drift measurements from the Republic of China Satellite-1 (ROCSAT-1). We select a quiet time period defined when Dst > −100 nT and K p ≤ 3. The ion drifts in the magnetic zonal direction are latitude (apex height) dependent and differ for different longitude sectors and seasons. Superrotation of the ionosphere is observed in the zonal drift measurements, particularly at the lower latitudes. The ionospheric superrotation generally decreases with increasing latitude and is attributed mainly to the F region dynamo where the features of the neutral wind and conductance affect the characteristics of the superrotation at different latitudes, longitudes, and seasons. We suggest that the latitudinal variation of the superrotation is mainly produced by the decrease in latitude of the neutral winds in the F region. A decrease of conductance with increasing latitude is also present, but evidence shows that neutral winds decrease faster with latitude than the conductance for high solar flux conditions. The longitudinal and seasonal variations of the superrotation are more influenced by changes in the F region conductance that is modified by vertical E × B ion drift motions and neutral wind-induced ion drift motions along magnetic field lines.

Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

“…These papers show data that have both similarities and differences to the results given in this paper. The zonal drifts derived from a limited amount of 2008 data in Pfaff et al (2010) show a similar pattern to other studies but with a more limited range of 25 m s −1 westward in daytime to 50 m s −1 eastward at night. The more extensive VEFI data set used in Fejer et al (2013) is binned so as to demonstrate seasonal variations of the zonal drift, but nevertheless shows great similarity to the data of Fig.…”

“…The nighttime zonal flow as measured would then probably be driven by neutral winds at off-equatorial latitudes whose electric fields would map along magnetic field lines up to the region of C/NOFS. During the solar maximum period of 1999-2003, Pacheco et al (2011 latitude variations of zonal drifts using measurements from the ROCSAT-1 spacecraft. They find that the eastward peak decreases in magnitude with increasing magnetic latitude, while the daytime westward flow is relatively stable suggesting that the decrease of superrotation with latitude is mainly produced by neutral winds that also decrease with latitude.…”

“…The local time variation of the east-west drifts has been examined by Maynard et al (1988), Coley and Heelis (1989), and Coley et al (1994) using DE 2 satellite measurements of the electric field during a high solar flux period. Near solar maximum Pacheco et al (2011) looked at magnetic latitude variations of zonal drifts using measurements from the ROCSAT-1 spacecraft. Recently, Pfaff et al (2010) have shown the first results for a limited period of 2008 of F region zonal and vertical drift from the Vector Electric Field Instrument (VEFI) instrument on board the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft.…”

“…Near solar maximum Pacheco et al (2011) looked at magnetic latitude variations of zonal drifts using measurements from the ROCSAT-1 spacecraft. Recently, Pfaff et al (2010) have shown the first results for a limited period of 2008 of F region zonal and vertical drift from the Vector Electric Field Instrument (VEFI) instrument on board the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft. Fejer et al (2013) also present VEFI results but for the more extended period of 2008-2011 observing longitudinal structure and wave-4 signature in the electric field.…”

Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations

“…The horizontal drift (e.g. Coley et al, 1994;Maynard et al, 1995;Fejer et al, 2005;Pacheco et al, 2011), on the other hand, has been given relatively less attention. Zonal drift of F region plasma is generally westward (eastward) during daytime (nighttime) (e.g.…”