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11 August, 2007
Average daily sunspot numbers were up a little, rising over five points
to 12.4. After a short period of no sunspots, we are back to seeing a
spot or two every day. Expect these conditions to continue, possibly falling
back to zero spots again around August 16-20.
Today (August 10) expect some unsettled to active geomagnetic conditions
due to a solar wind stream. Planetary A index predicted for August 10-16
is 25, 15, 5, 5, 5, 5 and 10. Geophysical Institute Prague predicts unsettled
to active conditions August 10, quiet to unsettled August 11, quiet August
12-14, quiet to unsettled August 15, and unsettled August 16.
New predictions for smoothed sunspot numbers in coming months seem to
appear almost monthly from the Space Environment Center. Now the estimate
for smoothed sunspot number in December 2007 has risen from 21 to 24.
You can see the prediction from last month at
http://www.sec.noaa.gov/weekly/pdf/prf1661.pdf
and the current one at http://www.sec.noaa.gov/weekly/pdf/
prf1666.pdf . Look on page nine of both issues.
Bob Wertz, NF7E was operating in Alaska last month, and wrote asking
about some strange conditions he observed on the air.
''Recently while on a mini DXpedition on Ushagat Island, located off
the coast of Homer, Alaska, we encountered some strange lulls in operating.
''We landed on the island on July 12, and after about 3 hours, we were
on the air and doing great. Then on the following few days, we almost
lost all communications with the world. At first we thought it was rig
problems, then antenna problems, but then realized it must be poor propagation.
''Can you give me some input about conditions those days?''
Yes, we can. Looking at data from the magnetometer at University of Alaska,
we see that the A index (called the College A index) on July 11-16 was
32, 10, 2, 39, 19 and 7. The cause was solar wind, and the disturbance
tends to concentrate toward the poles, so the absorption in Alaska from
this activity can lead you to believe your radio is dead.
Folks operating at high latitudes have had a respite from this activity
because during a lull in the solar cycle, the chance of geomagnetic storms
is much less. But old Alaska hands will
tell you of times in years past when geomagnetic storms seemed to last
for months, and HF was mostly unusable. That is the downside of higher
solar activity. We like sunspots, because of the accompanying increase
in reflection and refraction in the ionosphere. But along with that comes
greater chance of geomagnetic storms.
If you would like to make a comment or have a tip for our readers, email
the author at, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL Technical
Information Service at
http://www.arrl.org/tis/info/propagation.html.
For a detailed explanation of the numbers used in this bulletin, see
http://www.arrl.org/tis/info/k9la-prop.html.
An archive of past propagation bulletins is at http://www.arrl.org/w1aw/prop/
.
Monthly propagation charts between four USA regions and twelve overseas
locations are at http://www.arrl.org/qst/propcharts/.
Sunspot numbers for August 2 through 8 were 0, 11, 11, 11, 16, 13 and
25 with a mean of 12.4. 10.7 cm flux was 69.4, 70.4, 69.4, 68.9, 70, 69,
and 69, with a mean of 69.4. Estimated planetary A indices were 5, 4,
2, 2, 12, 23 and 6 with a mean of 7.7. Estimated mid-latitude A indices
were 5, 4, 0, 2, 8, 23 and 5, with a mean of 6.7.
Source: The
American Radio Relay League
•
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• All propagation
reports can be found at:
http://www.southgatearc.org/propagation
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