IMAGE electrojet indicators IL, IU and IE

IMAGE electrojet indicators are simple estimates of the total eastward and westward currents crossing the magnetometer network. Their definition is quite similar to that of the standard AL, AU and AE indices. For each timestep, IL(t) = min({∆X(t)}), where {∆X(t)} stands for the variation of (geographic) north components of the magnetic field measured at the selected stations relative to quiet time baselines. In the same way, IU(t) = max({∆X(t)}), and IE = IU - IL.

In determining the variations due to ionospheric/magnetospheric disturbances it is important to set the quiet time baseline values of the fields at the recording stations. Here the quiet time baseline is determined automatically by considering all 3-hour intervals 00-03, 01-04, ... , 23-24 UT in the selected time interval. The X range (max(∆X)-min(∆X)) at all sites is calculated for these intervals. The interval with the smallest average range is used as the baseline period for all stations.

Click the button below to enter the IMAGE electrojet index page.

The plots are only for quick-look purposes. For a detailed scientific analysis, we ask you to contact Ari Viljanen (ari.viljanen (at) Comments can also be sent to Lasse Häkkinen (lasse.hakkinen (at)

Updated: 19.12.2018 - LH