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

Abstract

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° away 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.