Spatio‐temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC‐C satellite magnetic measurements

Abstract

[1] The equatorial electrojet (EEJ) is an eastward electric current on the day-side, flowing in a narrow band along the dip equator in the ionospheric E region. Recent magnetic observations from the CHAMP, Ørsted, and SAC-C satellites, comprising more than 95,000 dip equator crossings from 1999 to 2006, have provided an unprecedented longitudinal coverage of the EEJ magnetic signature. We have used these data to construct an empirical model of the EEJ current climatological mean and day to day variability as a function of longitude, local time, season, and solar flux. Our model has been successfully verified against vertical drift data from the JULIA radar at Jicamarca. We have also used the EEJ observations to estimate the self-correlation of the EEJ, confirming short longitudinal correlation lengths of 15°and finding a temporal correlation length of 2.4 h. Our model's predictions of the eastward electric field and its standard deviation may provide useful input to various kinds of ionospheric simulations. Coefficients and software are available online at http://models.geomag.us/EEJ.html and http://www.earthref.org.Citation: Alken, P., and S. Maus (2007), Spatio-temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC-C satellite magnetic measurements,

Longitudinal and seasonal structure of the ionospheric equatorial electric field

“…DE3 "wave-4" structure has been found in many ionospheric data sets, including the EEF, equatorial electrojet current, and vertical ion drift velocities England et al, 2006;Alken and Maus, 2007;Lühr et al, 2008;Fejer et al, 2008;Alken and Maus, 2010b]. The wave-4 structure typically contains maxima over both Africa and South America.…”

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

“…The intensity of the equatorial electrojet also shows a solar cycle variation (e.g., Alken and Maus 2007;Bhattacharyya and Okpala 2015). Yamazaki et al (2010) demonstrated that the sensitivity of the equatorial electrojet to F 10.7 is approximately the same with the sensitivity of the global Sq current intensity to F 10.7 .…”

“…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). …”

Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview

“…Although the EEJ is known since many years from magnetic observations from ground (e.g., Onwumechili 1967;Forbes 1981), only satellite observations from Ørsted and CHAMP provided a global picture of the EEJ and its LT dependence (Ivers et al 2003;Lühr et al 2004). Alken and Maus (2007) derived a climatological model of the EEJ sheet current density based on Ørsted, SAC-C and CHAMP observations, describing its variability with longitude, season, local time, and solar flux. Comparing EEJ estimates based on CHAMP data with ground based magnetic data, Manoj et al (2006) revealed a longitudinal correlation length of the day-to-day variability of the EEJ of ±15 • , which has been attributed to similar characteristic lengths of the ionospheric conductivity.…”