Last night, it was reported that there was a coronal mass ejection (CME) that resulted in an aurora being seen as far south as Atlanta, GA. The aurora, more commonly known as the Northern Lights, are usually only visible as far south as the northern tier of the United States.
I knew something was up as soon as I turned on my rig last night. Nearly every signal had some auroral flutter on it. Auroral flutter is caused by radio waves bouncing off the ever-changing aurora or passing through it. When severe, auroral flutter can make a signal nearly unreadable.
Auroral flutter is usually limited to signals that pass over the North Pole. I first became aware of this phenomenon when I worked several stations in Northern Russia. Last night, though, even U.S. stations had this characteristic flutter. I was a little flummoxed by this. I’d never heard this on domestic QSOs.
I got to talking about this with Steve, N4LQ. He said that he was at first a little taken aback by the auroral flutter, because he had been fooling around with the receiver section of the HW-16 he was using and didn’t know if the odd sound he was hearing was the result of his experiments or band conditions. I assured him that it wasn’t the receiver. :)
Auroral flutter can be heard via back scatter (reflection from it) as well as forward scatter (transmission through it). If two stations are in the skip zone on a frequency above the MUF for their path, their signals will pass through the ionosphere without reflecting. It is possible they would only be able to hear each other via reflection off the ionized region of the auroral zone, which would have that characteristic flutter (which is variable doppler modulation due to the varying properties of the aurora). Below 10MHz most of us don’t have beams so our antennas usually radiate pretty much in all directions. During these periods of increased K index, effective MUF is also lowered which could also explain how this is often heard. HF is interesting as a hobby– a much more challenging medium than VHF for communications. I would hate to have to design a comm link depending on it!!
Similar conditions observed here in MA on 30M last night: very deep and rapid flutter on signals from 1s, 2s, 3s and 4s, which aren’t usually heard at night. There were media reports of auroras and meteor showers last night. Also, little European DX heard, making me wonder if auroras might’ve been reflecting their signals as well.
I have worked / attempted to work Project Deep Freeze stations with the frustration of auroral flutter via Antarctica. We were experimentally attempting to pass SSTV images back and forth in hopes of being able to send pictures of new born babies to the sailors “on the ice”, or family pictures of special events. It was most interesting how some pictures would pass when listening to the signals said NO! Likewise, when the signals sounded good, the images might be terrible.