Geomagnetic Storm Distorted on NVIS Signal

On July 15, 2000 there was a severe G5 category geomagnetic storm that began at about 1500 UTC. The Kp index reached 9. HF signals were were greatly attenuated and later that evening stations to the north were working auroral scatter on VHF. I had noticed for years in the past that HF signals would become very distorted in the 3-15 MHz range during geomagnetic storms. During this particular event I noticed that NVIS (Near Vertical Incidence Scattered) signals had the most distortion. Because of the straight up and straight back down reflection off of the ionosphere the great circle distance can be very short of course.

I recorded W5FRS at 2242 UTC on this day on the 30m band. According to QRZ.com he is located in Irving, TX which is only about 35 miles from me. As you listen to the recording you will notice that instead of a pure CW note, he has a tremendous distortion to his signal that varies with time. This is the same type of distortion caused by aurora scattered signals on VHF but at this time of the day the aurora was still very far north of my location. Other signals had distortion as well but the further they were from me, the less the distortion.

W5FRS


Spectrogram of the Signal


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