The field of the equatorial electrojet from CHAMP data

Abstract

Abstract. We apply a simple linear transform, the alongtrack second derivative, to four years of scalar and vectorial data from the CHAMP satellite. This transform, reminiscent of techniques used in the interpretation of aeromagnetic surveys, is applied either to the geocentric spherical components of the field or to its intensity. After averaging in time and space, we first produce a map of the crustal field, then maps of the equatorial electrojet field at all local times and all universal times. The seasonal variation of the electrojet, its evolution with the solar cycle, and the effect of geomagnetic activity are discussed. The variation of the electrojet with longitude, an intriguing feature revealed by satellite data, is described in some detail, and it is shown that this longitude dependance is stable in time. The existence of a counterelectrojet in the morning, everywhere except over the Pacific Ocean, is established. The signatures of closure electric currents and of interhemispheric currents are also evidenced.

The role of the vertical <I><B>E</B></I>×<I><B>B</B></I> drift for the formation of the longitudinal plasma density structure in the low-latitude F region

“…Oh (oh@spweather.com) 2007; Scherliess et al, 2008). The observations of similar periodic structures in the daytime equatorial electrojet (England et al, 2006a;Mouël et al, 2006) and equatorial vertical ion velocity on the topside (Hartman and Heelis, 2007;Kil et al, 2007) supported the association of the longitudinal density structure with the daytime vertical drift of equatorial plasma. The diurnal non-migrating eastward-propagating tide with zonal wave number-3 (DE3 tide) was suggested as the driver of the longitudinal variation of the vertical E×B drift (England et al, 2006a, b;Immel et al, 2006) and Hagan et al (2007) and showed the capability to produce the observed wave-4 density structure by the effect of the DE3 tide.…”

The influence of nonmigrating tides on the longitudinal variation of the equatorial electrojet

“…Longitudinal profiles derived from Ørsted observations have been presented by Jadhav et al [2002] and Ivers et al [2003]. Likewise, CHAMP data have been used by Lühr et al [2004] and Le Mouël et al [2006]. There are some common features in all these curves, e.g., intensity peaks over South America and Indonesia, but otherwise they differ considerably.…”

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

“…Early satellite observations showed diverse results (Cain and Sweeney 1973;Onwumechili and Agu 1981;Langel et al 1993;Kim and King 1999;Jadhav et al 2002;Ivers et al 2003;Lühr et al 2004). More recent studies have established that the longitudinal variation of the daytime equatorial electrojet intensity is often dominated by the so-called "wave-4" pattern with four peaks and four troughs between 0°and 360°longitudes (Le Mouël et al 2006;England et al 2006;Alken and Maus 2007;. Figure 56b (from Lühr and Manoj 2013) displays the longitudinal dependence of the equatorial electrojet intensity.…”

“…Since the difference between the black and gray lines does not depend much on the main field model, the derived EEJ field is robust to the selection of the main field model. For this reason, the Sq-EEJ separation is a common practice for EEJ studies based on satellite data analysis (e.g., Le Mouël et al 2006;England et al 2006;Manoj et al 2006;Alken and Maus 2007;Tomás et al 2008;Alken et al 2015). …”