ARRL Propagation Bulletin ARLP033 (2007)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 10, 2007
To all radio amateurs 

ARLP033 Propagation de K7RA

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

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 and the current one
at . 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

''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

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service at For a detailed
explanation of the numbers used in this bulletin, see  An archive of past
propagation bulletins is at .  Monthly
propagation charts between four USA regions and twelve overseas
locations are at

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