Dopplergram Catches a Solar Flare

Yesterday I took a day off from grabbing to try my new Dopplergram on the WWV 10 MHz signal.  As luck would have it an M-class Solar Flare occurred during the recording:

Figure 1.  Solar Flare of 18AUG12 as seen on Dopplergram

Figure 2.  Solar Flare of 18AUG12 as seen on 10 minute grabber

Figure 3.  GOES X-ray flux

An M-class flare commenced just before 1610z.  The increasing frequency means the path length was decreasing as the reflecting layer moved downward

This is the cleanest data I've recorded of a flare and justifies a calculation of Ionospheric motion from the observed Doppler shift.  I assumed a simple triangle relationship of the radio path (Earth's curvature ignored) and obtained distance parameters via the Internet and the take-off angle of the signal from W6EL's propagation program.  The calculations are as follows:

Figure 4.  Calculations of vertical velocity of Ionosphere in response to Solar Flare of 18AUG12

The estimated vertical velocity of the reflecting layer was ~ 250 km/hr for a 1 Hz shift or 750 km/hr (466 mph) for the maximum 3 Hz shift as seen in Figure 2.

If we assume the average speed was 104 m/s (corresponding to an average Doppler shift of 1.5 Hz) then the distance moved by the Ionosphere over a period of 45 seconds was  4.7 km which is small compared to the starting distance, h, of 217 km.  Thus h can be assumed constant.

Bottom line:  the Ionosphere moved vertically downward in response to the stimulus of the Solar Flare at an average speed of 500 km/hr (310 mph).

There is a nice discussion of the Doppler effect at Wikipedia and you can check my math since I've been retired for almost 20 years now and seldom use calculus any more.