On November 4, 2021, on the Russian national holiday, National Unity Day, also known as the Day of the Icon of the Kazan Mother of God, a strong Aurora took place.

Aurora is a solar-ionospheric electromagnetic phenomenon accompanied by a strong magnetic storm. Aurora always occurs in the near-polar regions near the north and south poles, when solar wind ions invade the Earth's atmosphere (caused by solar flares or emissions from the solar corona). On November 4, a level 7 magnetic storm occurred (very energetically powerful).

Image source: website spaceweather.com, NASA.

On this holiday, many radio amateurs turned on their transmitters and pointed their 144 MHz antennas to the north. In this case, horizontal polarization is used; for multi-element antennas, signal levels can reach S9 (depending on the antenna and transmission conditions). The reception sound is a hiss in time with the Morse code transmission.

I don’t have a VHF antenna pointing north, so I watched the work of radio amateurs and received several “traces” of reflections from the electronic “shower” during the Aurora on a regular pin.

To do this, I connected an RTL-SDR receiver on RTL2832U+R820T chips to a computer running the Linux Runtu Lite 20.04 operating system.

It took some time to install the GQRX program - a digital SDR receiver and DSP processor for Linux OS.

sudo apt-get update
sudo apt install rtl-sdr librtlsdr-dev
sudo apt install gqrx-sdr

Then I connected the headphones to the green jack on the back of the PC
and checked that the sound is working:

To check the sound, I often use the Mozilla FireFox browser and the Radio Day radio station website: https://radioday.fm closed, alternative -https://www.radiorecord.ru/station/eurodance.
The sound card works, there is sound in the headphones.
I had to turn down the volume using alsamixer (или sudo alsamixer) and pulseaudio system level control.

GQRX program settings:

In the top menu:

File - I/O Devices:
Device:Realtek RTL2838UHIDIR SN00000001
Device string:rtl=0

• Decimation:16(can be set from 0 to 16 depending on the required spectrum band resolution)
  Device:Built-in audio
  Sample rate:48 kHz

On the right side:

Input controls:
LNB LO: 0
✓ Hardware AGC
LNA:18db
Antenna:RX
✓ Reset frequency controller digits

Receiver Options:
Frequency:144060 kHz
Filter Width:User (0.9 k)
Filter shape:Normal
Mode:USB
AGC:Medium
Squelch:-130 db

FFT Settings:

• FFT size:65536(you can set it smaller if you don’t need high spectrum and waterfall resolution)
  Rate:25 fps
  Time span:Auto
  Window:Hann
  Averaging:75%
• Panadapter:25%
  *Frequency zoom:5x
• Colormap:Gqrx

After setting, you need to save them:
File - Save settings - default.conf

Settings are stored in a file ~/.config/gqrx/default.conf

Output sound to headphones or speakers - by pressing the leftmost button with the triangle symbol
*"Start DSP Processing"

Adjusting frequency, zooming and panning in GQRX

*Selecting a reception mode: USB/LSB/CW/N-FM is produced on the " tabReceiver Options" on the right side of the window.

*Rough Frequency Tuning receiver - by clicking on the upper or lower part of the digits of the frequency display.

*Frequency fine tuning receiver - by rotating the mouse wheel when the mouse cursor is on the spectrum or waterfall

*Zoom(zooming in or out) of the spectrum and waterfall - move the mouse cursor to the frequency scale between the spectrum and waterfall. The cursor will change to 4 arrows from one point. Now let's spin mouse wheel.

*Moving the Spectrum similar to zooming, but you need to “grab and pull” the frequency scale to the side.

*Changing filter cutoff frequencies and passbands
First you need to find the signal visually. Then adjust the frequency setting to the signal and increase the scale of the spectrum (zoom in), then move the mouse cursor to the edge of the translucent lighter area in the spectrum window and drag it with the left mouse button - do this for the lower and upper cutoff frequencies of the filter. In this way, you can highlight a weak signal against a background of noise by narrowing the filter bandwidth.

• Digital noise filter DSP on the right side of the window there are buttons NR1 and NR2. They can be turned on for better speech intelligibility in SSB (I have not tested it for Aurora).

Recording audio in GQRX

At the bottom of the window, the "Mute", "UDP", "Rec" and "Play" buttons are always available. Pressing the "Rec" button starts recording audio, pressing "Rec" again stops recording.

The files are saved by the program to the user's home folder ~/. (with WAV extension).