This
graph was created over BHM or universal time. It is a histogram for
geomagnetic storms with Kp greater than 6. This graph clearly
shows a maximum between 18 UT (1800 BHM on the graph) and 3 UT (300 BHM
on the graph). It also shows a minimum around 9 UT. This variation
is most interesting because Kp is a planetary index, which means that the
local time should make no difference. It may be night time for some
of the magnetometers but it may be day time for others. We believe there
must be a physical mechanism at work here.
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