A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations

Abstract

Detailed analysis of the scalar magnetic field data from Ørsted satellite for quiet days from April 1999 to March 2000 has been undertaken to study the equatorial electrojet (EEJ) phenomenon. An objective technique has been adopted for the identification of the EEJ from the satellite data and estimation of the standard parameters associated with it. EEJ strength computed using the satellite data and simultaneous ground magnetic observatory data, for the Indian and American sectors, correlate very well authenticating the method used. Estimated zonal variation in the EEJ parameters such as peak current intensity (J0), and total current (I+) are broadly consistent with the earlier observations. We, however, observe that the width of the EEJ varies considerably with longitude, a feature not seen in the Pogo data. The study shows that the EEJ axis (center of EEJ) closely follows the dip equator at altitude of 106 km, but there is a small departure that undergoes diurnal variation, with a minimum at noon. The globally averaged EEJ amplitude follows the expected diurnal pattern. Principal component analysis technique reveals that first four components can explain around two thirds of the electrojet variability. The first component, which contributes a little over 30% to the observed variance, could be identified with the global variation of the EEJ emanating from the day‐to‐day variability of the migrating tides. The second and fourth components, which account for around 15 and 10% of the variance, respectively, are driven by forcing that depends on whether the location of the EEJ in that sector is in the Northern or Southern Hemisphere. The third component provides maximum contributions wherever the geomagnetic and dip equators are sufficiently close, accounting for 12.5% of the variance. The remaining components could be associated with contribution of nonmigratory tides or other unknown mechanisms. Thus the present study suggests that besides conductivity, atmospheric tidal modes play important role in defining the zonal variability of the EEJ current system.

Asymmetries in the equatorial electrojet around N-E Brazil sector

“…As stated earlier, the EEJ centre in Brazil was located at 21±16 km south of the dip equator (Rigoti et al, 1999). Jadhav et al (2002) described analyses of scalar magnetic field data from the low orbiting Ørsted satellite from April 1999-March 2000 and concluded that the EEJ axis (centre of EEJ) closely followed the dip equator at an altitude of 106 km but there were small departures with the local time, with the minimum at noon. They also found that in the longitude regions near 39 • E, 285 • E and 315 • E the angular deviation of EEJ axis from the dip equator was systematically larger than 0.5 • .…”

“…Surprisingly they concluded that the electrojet current peaks right at the dip equator irrespective of season or longitude. They did not refer to earlier work of Jadhav et al (2002) on the same topic. 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.…”

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;.…”

Global characteristics of the lunar tidal modulation of the equatorial electrojet derived from CHAMP observations

“…Magnetic field satellite missions like Ørsted and CHAMP can help in this respect and map out the EEJ distribution world wide (e.g. Jadhav et al, 2002;Lühr et al, 2004). Only after considering a sufficient amount of satellite data the true longitudinal variation of the EEJ has been determined for the first time by Alken and Maus (2007).…”