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ARRL Propagation Bulletin ARLP025 (2005)

ARLP025 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 25  ARLP025
From Tad Cook, K7RA
Seattle, WA  June 17, 2005
To all radio amateurs 

ARLP025 Propagation de K7RA

If you look at the average of daily sunspot or solar flux numbers
for the past week, you'll see hardly a change from the previous
period. This does not mean there was no activity, or even 0
sunspots, but the average daily solar flux is exactly the same the
past week as the one previous, and the average daily sunspot number
was down by less than a point. Sunspot counts rose in the earlier
period, peaked at the end of that reporting week (which is Thursday
through Wednesday) and declined over the next seven days. Last
Friday, June 10, sunspots 775 and 776 were transiting the center of
the visible solar disk, which meant they were in the best position
for affecting Earth.

A Coronal Mass Ejection on June 9 caused a geomagnetic storm on June
12, when the arrival of the ejection and solar wind was met with a
south-pointing interplanetary magnetic field. When the field points
north, it helps protect the Earth from the effects of solar wind.
But when it points south, the Earth is vulnerable. On June 13 the
field again pointed north.

Currently we are experiencing effects from a coronal mass ejection
which swept over Earth around 0900z on June 16. This was a weak
disturbance, but it is followed by a moderate solar wind. The
expected planetary A index, a measure of geomagnetic stability world
wide, is expected around 25, 15, 10 and 8 for June 17-20. Solar flux
is expected to remain below 100 until the end of this month.

Currently there is a large sunspot detectable on the far side of the
sun. A large sunspot, number 779, which only emerged this week is
currently at the center of the visible solar disk, directly facing

Now let's look at ARRL Field Day, a very popular activity which
generates a great deal of interest and mail this time of year. The
dates are June 25-26, and recurring coronal holes and a high speed
solar wind are expected to result in active to minor storm levels
around June 24-27. It is difficult to predict with real accuracy
this far out, but according to the U.S. Air Force the expected
planetary A index for June 24-27 is 15, 20, 20 and 15. Solar flux
around that weekend is expected around 85-90. By the way, I found an
interesting article titled, "Air Force Space Weather Troops," which
is about a solar observatory the Air Force operates in Puerto Rico.
The article can be found on the web at,

Next week we'll revisit Field Day in the hours leading up to next
weekend. Meanwhile, this weekend in addition to other activities is
the All Asian DX CW Contest, SMIRK 6-meter Contest, and the Kid's
Day Operating Event. For Kid's Day info, check Next week is also the
summer solstice, the longest day of the year in the Northern
Hemisphere, June 21. This day gets really long the farther north one
moves in the Northern Hemisphere. For instance, on June 21 in Los
Angeles the sun will rise at 5:50 AM and set at 8:01 PM, a 14 hour
and 11 minute period. But in Seattle, the sun rises 29 minutes
earlier at 5:21 AM and sets a whole hour later than L.A. at 9:01 PM,
a 15 hour and 41 minute period from sunrise to sunset.

Another email arrived concerning 6 meter openings. Eric Hall, K9GY
was operating on Saturday, June 11 from grid square FM08rp at 3,500
feet elevation west of Shenandoah National Park in northeast
Virginia. He was mobile with a 6 meter whip on his car top, and
heard VP5/N4VHF in FL31 (Turks and Caicos Islands). Eric feels he
nearly worked him when the other station asked for a repeat from the
Yankee station. He worked stations in FN11, FN20, FN21, FN00, FN01,
FN30, FN31, FN32 and EM96.

If you want to locate those grid squares, check the Grid Square
Conversion site at It will
give you latitude/longitude coordinates for any grid square, and
also works with the more precise 6 character locator. Running it to
find my grid square from map coordinates, I discovered my 6
character locator is at CN87uq.

If you would like to comment or have a tip, email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
bulletins is found at,

Sunspot numbers for June 9 through 15 were 99, 103, 85, 85, 73, 44
and 64 with a mean of 79. 10.7 cm flux was 116.1, 114.3, 108, 103,
91.8, 93.8 and 94.5, with a mean of 103.1. Estimated planetary A
indices were 5, 5, 6, 35, 33, 10 and 21 with a mean of 16.4.
Estimated mid-latitude A indices were 3, 2, 6, 23, 17, 8 and 14,
with a mean of 10.4.


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