Noon‐time equatorial electrojet: Its spatial features as determined by the CHAMP satellite

Abstract

[1] New observations obtained by the satellite CHAMP reveal a detailed picture of the noon-time equatorial electrojet (EEJ). The low orbit of CHAMP and its high-precision magnetometers reveal the spatial structure of the EEJ with unprecedented accuracy. Data from more than two and a half years have been used to investigate average features and also the global characteristics of the EEJ. Rather than interpreting the magnetic signatures, we determined the horizontal current distribution by using a very general current model (series of line currents). This makes the results independent of satellite altitude and ambient field geometry. The procedure for determining the structure of the electrojet is fully automated, giving an objective response. Some of the spatial features of the noon-time EEJ are as follows: The electrojet current peaks right at the dip equator. There is no deviation from it either on a seasonal basis or with longitude. The width of the EEJ (%4°in latitude) at half the peak value of the current density profile is for a given longitude fairly constant, independent of the amplitude. Return currents north and south of the eastward current are a common feature of the EEJ. They peak at latitudes some 5°a way from the dip equator. The intensity of the EEJ varies strongly from day to day. The average peak current density exhibits a clear dependence on longitude. Peaks show up over South America and Indonesia. The average current density follows closely the monthly mean of the solar flux index, F10.7. The total EEJ eastward current is about three times as strong as the return current. The total current and the peak current density are related to each other by a power law. This suggests that the longitude dependence of the EEJ intensity can be explained by the varying cross-sectional area of the Cowling channel.

Variability of the ocean‐induced magnetic field predicted at sea surface and at satellite altitudes

“…The former data set was created to demonstrate that our data analysis approach does bring out field variations (of any origin, including ionospheric) with relatively short spatial scales, even if their magnitude is less than a few nT: as anticipated, one of the prominent features in Figure 9 is the Equatorial Electrojet (EEJ) which is observable only at daytime hours and is characterized by rather short spatial scales. Its position and width are in good agreement with previous, much more elaborate analyzes [e.g., Lühr et al, 2004]. The absence of EEJ in the top panel of Figure 9 is due to the fact that zonal electric currents dominating EEJ induce only vertical and meridional components of the magnetic field.…”

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

“…A number of review articles exist about the equatorial electrojet (see Table 1), and the interested reader is referred to those reviews for early development of the topic. Satellite measurements have revealed that the center of the equatorial electrojet exists right above the magnetic equator (Lühr et al 2004). The effective zonal ionospheric conductivity, the so-called Cowling conductivity, is locally enhanced along the magnetic equator, which gives rise to the strong zonal current of the equatorial electrojet.…”

“…The Sq-EEJ separation is generally done by some type of curve fitting to the middle-and low-latitude data, which does not reflect any physical process. Figure 16 is an example of the curve fitting (Lühr et al 2004). In the figure, the black line is the residual field after the subtraction of the main field model from the raw data, and the green line is a fit to the large-scale field.…”

Longitudinal and seasonal structure of the ionospheric equatorial electric field

“…[7] Lühr et al [2004] present a method of deriving equatorial electrojet current flow from CHAMP satellite magnetometer measurements. CHAMP's near-polar orbit with an inclination of 87 enabled it to record full latitudinal magnetic profiles of the daytime equatorial region for each orbit.…”