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A measure of the variability of GCP data
(the variance across EGGS) collected on
September 11 2001 becomes unusually large early in the morning, and it
continues to be extreme until around 11:00 EDT, after which it becomes
compressed for most of the rest of the day.
This figure displays the accumulating departures of the variance from
its expectation, and the strength and persistence of the deviations are
evidence that the EGG network responded to the events of that day.
The changes in variance look like a typical random walk for a
few hours, and then begin an extraordinary departure that peaks at
11:00, about the time the full magnitude of the terrible
events has become clear.
The range of deviation of the variance on 9/11 is
unique in the GCP database.
The version in place has timing set to show the 24-hour period in 15 or 20
seconds. But the display will be constrained by the speed of your processor.
Use your browser's back and forward buttons to replay.
(Note: the animated clock is not exactly synchronized, but the x-axis
time labels are correct.)
Author: Greg Nelson, 19 Sept 2003
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