[time-nuts] Re: BOAT ionospheric effects

[Andrew Kalman]

Oooh, that brings back memories -- I built/assembled some of electronics of
the VLF stations in the ERL building (long gone) as part of my student job
at Stanford working for Tony Fraser-Smith, and I had Umran for a class as
part of my EE curriculum -- convinced me that E&M was not my area of
strength :-)

--Andrew




On Sat, Oct 22, 2022 at 3:58 AM Phil Erickson via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi all,
>
>   John Ackermann mentioned this thread.  I'm an ionospheric observational
> physics person.
>
>   The disturbance from a gamma ray flare is primarily on VLF propagation
> (10s of kHz) because it penetrates so low in the atmosphere and enhances
> the "sub-D region" between 40 and 80 km or so.  D region is highly
> absorptive due to strong ion-neutral collisions in events where it gets
> enhanced.
>
>   VLF ionospheric propagation effects from gamma ray bursts weren't really
> confirmed until this 1988 Nature paper by Fishman and Inan on a strong 1983
> burst:
>
> Fishman, G. J., and U. S. Inan. "Observation of an ionospheric disturbance
> caused by a gamma-ray burst." Nature 331, no. 6155 (1988): 418-420.
> https://www.nature.com/articles/331418a0.pdf?origin=ppub
>
>   There are a number of publications since that one.  Because VLF paths are
> inherently transcontinental and interhemispheric in the earth-Ionosphere
> waveguide (ground to bottom of the D region), this was seen only on a very
> long path reception.  Check out Figure 2 - I think that's one of the
> reasons why it took so long to conclusively identify it - as they say:
>
> "Figure 2 shows a portion of the record from the three stations between
> 21:40 UT and 23:00 UT on 1 August 1983. A clear indication of a disturbance
> beginning at 22:14:10±10UT is seen in the radio station GBR signal. Weaker,
> barely detectable decreases in amplitude are seen simultaneously in the two
> other signals. Without the GBR signal, these other two signals alone would
> have been considered uneventful as similar weak fluctu- ations are seen in
> their records near the time of the burst. The disturbance in the GBR signal
> differs in its rise-and-fall time from any other disturbances seen within
> 60 h of the burst."
>
>   So identifying the spike using multiple simultaneous receptions was
> needed to disambiguate it from something like whistlers (lightning), flares
> (SIDs), etc.  The SpaceWeather article that Bob KB8TQ mentioned shows a
> similar type of detection of the recent super-GRB.
>
>   Back to the topic though: the ionization deposit would be very wide
> spread (not localized) and would however I think contribute not very much
> to the total electron content (TEC), which is of course the critical thing
> for dual frequency GNSS measurements at L band.  The way I could see
> something occurring is if irregularities were created in the region of
> enhanced ionization, but they wouldn't last too long.
>
>   Consider also that the ionosphere's natural electron density variability
> is 1 to a few % on any day of the year, and you can see this clearly in
> differential TEC from things like traveling ionospheric disturbance (TID)
> waves and the like (many many studies).  Those don't significantly impact
> timing solutions due to the dual frequency nature of the GNSS system which
> subtracts out ionospheric delay, so I can't imagine this event would change
> those either.
>
>   Of course, I could be wrong - please correct!
>
> 73
> Phil W1PJE
> MIT Haystack Observatory
> Westford, MA
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