To display the time variation of the auroral currents, we examine 45 minute windows of data and evaluate quantities indicating the location and intensity of the magnetic perturbations. The window is advanced in 15 minute steps providing the time series shown in the time history plots. The top two panels show the fraction of magnetic field samples that were above threshold (typically ~100 nT) in 2 degree magnetic latitude bins for the northern (top) and southern (second) hemisphere. In this analysis, latitude is evaluated from a point offset 3 degrees toward midnight to center the position on the average center of the auroral oval.

The average fit to the auroral electrojet location and its latitudinal extent is indicated by the three white traces in the top two panels. These traces show the latitude of the electrojet fit (center trace) together with the 20% and 80% levels (upper and lower traces) to the 45 minute window of data. Gaps in these traces correspond to intervals when no fits are possible.

Black cityscape traces show the poleward and equatorward range of magnetic latitudes used to evaluate the perturbation intensity statistics shown in the 3rd through 6th panels of the plot. If no range could be evaluated automatically, a default range from 70 to 90 degrees in the north (-70 to -90 in the south) is used. This range whether fit or default, reflects the total latitude range over which auroral perturbations were detected.

The intensity of auroral magnetic perturbations is also of interest and the 3rd through 5th panels show statistics of the magnetic perturbations. The data above detection threshold are first ranked by the eastward magnetic perturbation. The traces show averages over the 95-100% and 45-55% percentile ranges, for various binnings of the data. The "Net dB" panel is calculated from all of the data while the "Day" and "Night" panels are from dayside and nightside data, respectively. The "Day" and "Night" panels also show the percentile averages evaluated separately for positive and negative eastward perturbations. Because the sense of perturbations are reversed in the southern hemisphere relative to the north for the same sense of field aligned current, data from the southern hemisphere are reversed in sign before being included in these calculations.

The "Net dB" panel shows the difference between maximum positive and negative eastward perturbations. The 95-100% trace, upper curve, gives a useful single parameter measure of the maximum strength of the magnetic perturbations and the 45-55% trace indicates the average. Satellites traversing the latitude ranges of auroral perturbations, shown in the upper two panels, observed average cross track departures from the Earth's field given by half of the 45-55% curve and maximum perturbations of about half of the 95-100% curve. On quiet days the 45-55% and 95-100% levels are below 200 nT and 400 nT, respectively. For active days however, these levels can rise to over 500 nT and 2000 nT. Typical values are ~300 nT for the 45-55% level and 500 to 1000 nT for the 95-100% level.

The "Day" and "Night" panels show similar percentile band averages for negative and positive eastward perturbations. From top to bottom the curves give the positive 95-100%, positive 45-55%, negative 45-55% and negative 95-100% averages. The reason for separating positive and negative senses is that the different signs correspond to distinct senses of auroral current which is especially important on the nightside. At night, the negative perturbations are typically larger than the positive, indicative of activity related to a well known phenomenon called "substorms". Separating these signals by day and night has never been possible before (because the ground stations are too far equatorward to pick up the dayside signals) and promises to give important new insight into the behavior of the magnetosphere-ionosphere system.

The bottom panel shows the daytime and nighttime ratio between the Net dB evaluated separately from northern and southern hemisphere data. Values different from 1 reflect hemispheric differences which are most likely due to differences in ionospheric conductivity. Inter-hemispheric comparisons have never been made before because there simply aren't sufficient ground stations in the southern hemisphere to yield meaningful comparisons. Based on the first six months of Iridium data we expect to see a strong seasonal variation in these ratios which will provide definitive evidence for ionospheric conductivity control of the magnetosphere-ionosphere interaction which has been much debated but never demonstrated observationally.

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