Equatorial electrojet from Ørsted scalar magnetic field observations

Abstract

[1] Previous studies of the longitudinal variation of the local noon electrojet have yielded doubtful results either because of the poor data quality or because the local times of equatorial crossings occurred in the early morning or late afternoon. The recent launch of the Ørsted satellite in a near-circular orbit with slow drift in local time of equatorial crossing has provided the opportunity for researchers to study the electrojet more accurately. Most studies remove the main field using a spherical harmonic model and then search the daytime equatorial passes for the distinctive electrojet trough in total intensity. The present study examines the electrojet for two consecutive 6-month periods and consequently two local time ranges. Pure signal processing is used to remove the main field directly. The residuals are binned separately for night and day passes on a 1°by 1°grid to enhance the signal to noise ratio and are bin centered by a least squares fitted linear model to compensate for the variations in satellite altitude. Thereafter, for each period the compensated night and day binned values are subtracted from each other to produce a difference set. Global plots of the subsequently spatially filtered difference sets reveal an almost constant electrojet 1/e half width of 3°, as seen at satellite altitude apart from a region in the western Pacific. There are four maxima in the electrojet amplitude at 0°-30°E, 90°-120°E, 180°-220°E, and 260°-290°E in each local time range.

Regular daily variations in satellite magnetic total intensity data

“…In particular, it can be seen that the equatorial electrojet forms in the morning hours after sunrise, and, exists from the pre-noon hours until sunset. See Ivers et al (2003) and Lühr et al (2004).…”

Asymmetries in the equatorial electrojet around N-E Brazil sector

“…One has to examine why the analyses of satellite data by different scientists do not agree with each other and why the conclusions Luhr et al (2004) are not in conformity with the ground magnetic field measurements. Ivers et al (2003) have discussed in detail the reasons for the equatorial electrojet profiles being different from the ground and satellite measurements. They suggested that the combination of long-track and spatial filtering of the satellite data modified the characteristics of the raw electrojet signature.…”

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;.…”