Professional, Citizen Research Suggests Eclipse Affected HF Propagation:
The ARRL Letter
September 7, 2017
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More Professional and Citizen Research Suggests Eclipse Briefly Affected HF Propagation:
Both professional and citizen scientists conducted formal and informal
investigations into the effect of the August 21 solar eclipse on HF
radio propagation. Nathaniel Frissell, W2NAF, of HamSCI
http://www.hamsci.org, has said it will take some time to get a more
scientific analysis of data that was compiled during the Solar Eclipse
QSO Party. He and others are investigating whether the sudden absence
of sunlight during the eclipse -- and especially of solar ultra-violet
and x-rays -- would briefly change the properties of the upper
Professional ionospheric researcher Dr. Phil Erickson, W1PJE, head of
the Atmospheric Sciences Group at MIT's Haystack Observatory
http://www.haystack.mit.edu/atm/mho, said he can say categorically
that there was a definite, large, and measurable effect in the
ionosphere from the eclipse.
"We saw a 2X reduction in electron density during the eclipse for at
least 45 minutes to 1 hour," Erickson told ARRL. "This reduction had
direct impacts on HF propagation along the bottom side." Erickson said
many models and observations exist from previous eclipses that
demonstrate these effects. Erickson said MIT researchers used a
"megawatt-class Thomson scatter radar," which can directly measure the
plasma state of the ionosphere, including electron density, across a
huge area in the eastern US.
"Scientists in the worldwide space physics community will be using
these and many other eclipse observations to learn more about our
ionosphere, space weather, and its effects on navigation and
communication signals including Amateur Radio," Erickson said. He has
shared his data with the HamSCI team.
Bob Reif, W1XP, was in southeastern North Carolina where the eclipse
totality was about 97% with two radios running multiple bands of WSPR.
"Lots of data to look at," he said, "but what jumped out was that at
almost the exact time of maximum coverage of the sun at this location,
160 meters opened for about 30 minutes and then closed down again until
the normal gray line. So, the D layer responded to the shadow of the
Moon to some extent."
Gene Greneker, K4MOG, in Georgia told ARRL that his own eclipse
experiment "worked out rather well." He set up an RFSpace NetSDR
receiver at his location, locked to a 10 MHz GPS standard and tuned to
WWV on 15 MHz. "The NetSDR provides in-phase and quadrature components
of the WWV signal, which allows relative signal phase to be
reconstructed from recorded data," Greneker explained in a
more-detailed account. "Signal phase-vector rotation change was chosen
to indicate totality arrival, because phase is very sensitive to any
change in propagation path length, possibly caused by ionospheric
movement, up or down. Solar presence or absence can cause vertical
Greneker recording the phase of the 15-MHz WWV signal from 1800 UTC
until 1900 UTC on August 21. "Each time the path length changes by 1
wavelength, there is a 360° change in the phase of the signal," he
said. Greneker offset the path of totality to the south, running
parallel to the path between WWV in Fort Collins, Colorado, and his
location in Atlanta.
Greneker assumed that the reflection point off the ionosphere was south
of Kansas City, and, he said, the minimum dip in the phase record
occurred very close to totality at that location. "At 1809 hours UTC,
when the totality point was parallel to the midpoint of the propagation
path, the path length increased from zero wavelengths to 157
wavelengths, or 3,140 meters, during the intervening 9 minutes," he
reported. As totality moved southeast, solar radiation began to
increase and the path length decreases as the ionospheric reflecting
point moves downward.
Bob Skaggs, KB5RX, told ARRL he spent about 4 hours in the central part
of Mission Valley, Montana, listening to conversations on various
20-meter frequencies with a low antenna. "At maximum of the eclipse,
the propagation went almost to nothing for maybe about 15 or 20
minutes," he said. "As the eclipse receded, signals came back up."
Skaggs tried 17 meters for 5 minutes at 1800 UTC and heard "no signals
He also said the local animal population responded to the eclipse as if
evening were approaching.
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