Effect of GNSS Degradation During Geomagnetic Storm 9/19-20/23

[Jonathan]

A really cool effect was observed on the VLF system during the strong geomagnetic storming of 9/19 and 9/20. I believe that the scintillation of the GNSS signal during that period produced a lot of error in the timing solution of the GNSS receiver which resulted in a sawtooth characteristic in the absolute phase measurement in NAA, which that measurement is referenced to GNSS timing. This geomagnetic storming event caused visible aurora, characteristic of low latitudes (red emissions) across Pennsylvania. 

Here is the plot of the NAA diurnal on 9/19/23 showing the effect of the scintillation in the absolute phase measurement as well as two SIDs caused by solar flares:

And on 9/20/23, showing more SIDs and the sawtooth effect past the initial onset of the geomagnetic storm:

Not only that, the nighttime portion of the diurnal (00:00-10:00) show the D layer being affected by the CME, showing different absorption variation than the night before. There are some SIDs as well, so these plots are indicating quite a bit of activity and a really nice observation.

Jonathan

KC3EEY 

  

[Jonathan]

Come to think of it, does anyone have access to GNSS TEC plots from GNSS receivers in Pennsylvania or surrounding states on both days?

Jonathan

KC3EEY 

[John Ackermann]

In a rush right now so more later, but I've been monitoring four GNSS/GPSDO for the last few weeks trying to catch correlations with space weather events.  I'll post more details later today.

John

[John Ackermann N8UR]

The more detailed reply promised earlier:

After talking with Nathaniel and Phil E. earlier this summer we thought
an experiment to see whether GPSDOs are affected by geomagnetic activity
would be a good idea.

My hypothesis is that the low pass filter characteristic of the loop
disciplining the oscillator to the GPS timepulse will tend to filter out
transient effects. The narrower the filter (the longer the time
constant) the more the attenuation.

Since Sep. 5 I have been using four NanoVNAs with the TinyPFA firmware
to monitor the frequency of four devices against a passive maser:

(a) Bodnar Mini GPSDO
(b) u-blox NEO-M8T timepulse at 10 MHz
(c) a version of BG7TBL GPSDO with OCXO
(d) a Trimble Thunderbolt configured with a 250 second time constant

The raw NEO-M8T has essentially no filtering at all, the Bodnar a time
constant of a few seconds, the BG7TBL around 50-100 seconds, and the
Thunderbolt 250 seconds.

My hunch is that the impact of the TEC change isn't large relative to
the normal short-term noise of GPS, and with low pass nature of the
GPSDO control loop we are unlikely to see effects above the noise level
unless there's a really big event that happens very quickly.

In a quick look at the data around 9/19 and 9/20 I don't see any obvious
blips in any of the traces. However, that's by eyeball using simple
averaging to reduce the short-term noise. The averaging might well hide
the transients we're looking for.

I would like to recruit someone with better analytic skills than I to
help post-process this data to see if we can pull out any transients
that correlate to solar activity. Any volunteers? (Seriously.)

73,
John
----

On 9/25/23 06:55, Jonathan wrote:
> A really cool effect was observed on the VLF system during the strong
> geomagnetic storming of 9/19 and 9/20. I believe that the scintillation
> of the GNSS signal during that period produced a lot of error in the
> timing solution of the GNSS receiver which resulted in a sawtooth
> characteristic in the absolute phase measurement in NAA, which that
> measurement is referenced to GNSS timing. This geomagnetic storming
> event caused visible aurora, characteristic of low latitudes (red
> emissions) across Pennsylvania.
>
> Here is the plot of the NAA diurnal on 9/19/23 showing the effect of the
> scintillation in the absolute phase measurement as well as two SIDs
> caused by solar flares:
>

> And on 9/20/23, showing more SIDs and the sawtooth effect past the
> initial onset of the geomagnetic storm:
>

> Not only that, the nighttime portion of the diurnal (00:00-10:00) show
> the D layer being affected by the CME, showing different absorption
> variation than the night before. There are some SIDs as well, so these
> plots are indicating quite a bit of activity and a really nice observation.
>
> Jonathan
> KC3EEY
>

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[Jonathan]

Hi John,

The effect on GPSDOs, even with shorter low pass filter periods should be very minimal during these disruptions, right?. In most applications by HamSCI and related members, the use of GPS is almost always in GPSDOs generating frequency references and not really for timing, so these sorts of disruptions have minimal impact on the application of frequency references as long as they are using a GPSDO and not just a GPS receiver in the short term, and most of these disruptions are short term in nature. I would bet that other than the M8T, there would be a very minimal effect in the data on those days.

For timing, like absolute phase measurements of VLF transmitter signals and applications with similar timing precision such as sferic location, GPS-locked amateur radio transmissions at VLF, and VLF interferometry with multiple receivers, these sorts of disruptions create errors in timing, even on the short term, so the use of a GPSDO, not as a frequency reference, but a timing reference, would be useful to make the VLF system more robust during CME events. I know the Trimble Thunderbolt and Mini TT both have 1 PPS output, but I don't know if the others do. For an "embedded" GPSDO, the Mini TT is the best choice due to its small footprint.

Jonathan

KC3EEY

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[Graham c]

Jonathan,

You may already be well aware but on the off chance you are not, there are a number of Canadian locations along the north shores of lake Erie and Ontario as part of the Canadian Active Control System ( ACS ) https://webapp.csrs-scrs.nrcan-rncan.gc.ca/geod/data-donnees/cacs-scca.php  which provide data that is used for ionospheric purposes https://meteospatiale.gc.ca/data-donnee/ionosphere/index-en.php 

Historical TEC data can be either plotted ( jpg or png ) or as an HTML table from here: https://meteospatiale.gc.ca/data-donnee/ionosphere/tec-arch-en.php

I would guess from your work that you are already aware and I am just preaching to choir but there may be others on the list who are not aware and may find this data interesting.

cheers, Graham ve3gtc

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[Jonathan]

Graham,

Thanks for posting those links. I don't utilize TEC data because it doesn't relate to my study, but time series TEC data will show scintillation on GNSS signals which would be useful in this case. I've only ever had these anomalies where geomagnetic storming affected my local region of the ionosphere which includes when aurora was observed in my state. Once I find some scintillation data for that day, I'll try to do some correlation.

Thanks again.

Jonathan

KC3EEY

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