Big Solar flare 2023-12-14 around 17:00 utc

[Graham c]

I walked into the lab just after noon local time ( 17:00 utc ) and noted an absolute lack of signals ( WWV, and WSPR/FST4W ) on 40m and 20m.

Checking the GOES X-RAY Flux web page https://www.swpc.noaa.gov/products/goes-x-ray-flux I noted the class X2.8 flare that occured around 17:00utc.  There were also a couple of smaller flares ( M5.7 and M2.3 ) earlier in the day as well 

This is what was displayed on my Spectrum Lab doppler gram display for WWV 15MHz

It will be interesting to compare to the plot from the Grape1-drf data.

cheers, Graham ve3gtc

[Jonathan]

Graham,

This flare was the biggest and longest duration I've ever captured on my system:

Notice the phase ambiguities at the onset and end of decay, as well as the inverse effect on amplitude with the SID occurring ~14:00.

The compressed spectrogram of sferics on that day shows similar effects:

Notice the D layer absorption of sferics starting at ~17:00 in the ~6-8 kHz band! The decay seen in NAA is similar to the decay in D layer absorption within that band. Since it's wintertime at the VLF receiver locally, sferics were pretty distant and can be used as a very useful ionospheric sounder! The period from ~3-3:30 looks to be a local power outage and the band at ~3 kHz is local interference caused by the mains connected loads.

Jonathan

KC3EEY

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[Jonathan]

Hi Steve,

I don’t use SuperSID, so I don’t know what the amplitude values mean, but what specifically don’t you understand? Some flares, depending on the region of the ionosphere they enhance ionization in and where on the great circle path they hit can cause a diminishing in signal at the receive site. This was seen at the first flare. Most cause an enhancement in propagation which is what was seen at the big flare. Your plot of NAA looks similar to mine, so the system is working correctly. 

Your loop in your attic and your VLF3 are picking up the same thing, but I’m glad you are going into the country to use your VLF3 for listening. If you live in a rural area, powerline hum and harmonics can often be filtered, but if you live in a suburban/urban area with dense power lines, it may not be able to be filtered well, often due to clipping somewhere in the receiving chain or at the soundcard, or both. With strong hum, powerline harmonics can often extend up to 30 kHz in the worst cases, showing up as regularly spaced lines in a spectrogram. 

I use vlfrx-tools. It's an open source, command line based tool set used to capture, analyze, record, and visualize the VLF spectrum. It also automatically detects whistlers and dawn chorus. It has an extensive documentation page, and there is a Raspberry Pi install guide to set up a whole set of functions, not just SID monitoring. It has the option to utilize a GPS PPS on the second channel of the soundcard for audio clock correction, sample realignment, and GPS timestamping. A network of VLF receivers can even be used as a lightning location network using vlfrx-tools software. There is a lightning location network that uses a similar VLF active antenna and Raspberry Pi called the ILDN and you can read about it here and see real time lightning maps of India. Currently, the SuperSID project does not accept data from vlfrx-tools as far as I know, so on your Pi 4, you'll have to run either one or the other. If you run SuperSID just for yourself, you can just use vlfrx-tools instead. 

The VLF receiver I used is a similar design to the VLF3, except it uses a single op amp on the frontend and a line driver IC and power converter as part of a VLF active antenna connected to a Pi 3 with a soundcard and GPS running vlfrx-tools. You can see captured whistler and dawn chorus events from my system here.

Jonathan

KC3EEY

On Sun, Dec 17, 2023 at 3:57 PM Stephen Martin <stephencl...@gmail.com> wrote:

Jonathan,

I'm new to VLF monitoring so I hope you will excuse my elementary questions. I am using a SuperSID receiver connected to a 96k sampling audio hat on a Raspberry Pi 4B running the SuperSID software. My antenna is roughly at 2 foot x 2 foot square with 50 turns of wire on it mounted against a south-facing gable wall in the attic. I keep the system running 24/7. I also have one of the NASA VLF-3 receivers; however, my location in a subdivision is so noisy with 60 cycle hum that I cannot use it. I have to head for the countryside to find a quiet location. If you have time, I'd appreciate your review of my data for the 14th. I've attached a plot as well as the data in a .csv file produced by the SuperSID software. I can see the impact of the big solar flare around 17:00 UTC on signals from NAA and NAU monitored here at my location in Evans, GA.  I don't understand why the amplitudes vary the way that they do, though.

Could you tell me about your installation? I am curious to know how you are able to capture and display the sferics. What software are you using?

Thanks in advance for your patience with this newbie.

Sincerely,

Stephen, KO4CVU

[Jonathan]

Stephen,

For converting wav files to vt format, use the vtwavex utility. First, ensure there is only a single channel in the wav file with sox and extract only that channel if necessary. Then, use vtwavex:

vtwavex source.wav > source.vt

vt means a timestamped stream and your wav files don't have that, it's best to ascertain the closest time as you could that the recording was started, say 2023-12-20 at 15:31 UT. Then, you would use:

vtwavex -T2023-12-20_15:31 source.wav > source.vt

Now, your converted file will have a somewhat accurate timestamp, and this is important for other signal analysis.

Jonathan

KC3EEY

On Wed, Dec 20, 2023 at 1:15 PM Stephen Martin <stephencl...@gmail.com> wrote:

Jonathan,

I think I'm beginning to understand the decay that I observed now.

That Install guide is REALLY helping me. I had been trying to use the vlfrx-tools software to analyze some .wav files that I had recorded with the VLF-3 receiver and a Tascam DR-5X digital stereo audio recorder (which does sample at 96K). But I was stumbling around with little success. The "Notes" file for vlfrx-tools was somewhat helpful but didn't really explain things in a way that I could understand and apply to what I was trying to accomplish. Thanks again for that link!

Stephen C. Martin, KO4CVU

[Dr. Rich Russel]

Nathan,

SARA members wrote the new Antennas for Radio Astronomy Section in the new ARRL Antenna Book (25th Ed)

We gave a plug for HAMsci on the first page! (p22.51)

Rich

SARA President

[Dr. Nathaniel A. Frissell Ph.D.]

Thank you, Rich!

 

Congratulations on the new chapter, and thank you for the plug!!

 

73 de Nathaniel W2NAF

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