(I sent this out to the group yesterday, but it seems to have not made it.)
I’ve been downloading and processing GPS data from Auckland, NZ, for evaluating the new SWPC WAM-IPE model, and today’s discussion moved me to look for eruption signals in those data. The attached plots are relative TEC measurements from two GPS satellites, PRNs 10 and 23, which were passing close to overhead at Auckland around the time of the eruption. The top panel in each is the relative vertical Total Election Content (TEC) for a four hour period including the eruption, the middle panel is the output of a high-pass filter on the data in the top panel with a cutoff at 1/512 Hz (including structures in the upper panel with time spans of 512 seconds or shorter), and the bottom two panels show the elevation-azimuth from Auckland to the satellite (left) and the location of the 275-km penetration point of the raypath from Auckland to the satellite.
The heavy red line in the top panel is the time of the main eruption, and the green and black lines are the estimated arrival time of a signal from the eruption for propagation velocities of 600 m/s (green) and 300 m/s (black). These velocities are the approx. velocities in the ionosphere and at ground level, respectively.
I think there is a clear signal of the eruption in the data from both satellites. I haven’t decided what to think about the arrival of more small-scale structure after the ground-speed arrival time, but it’s interesting.
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