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ARRL Propagation Bulletin ARLP029 (2005)

ARLP029 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 29  ARLP029
From Tad Cook, K7RA
Seattle, WA  July 15, 2005
To all radio amateurs 

ARLP029 Propagation de K7RA

The big patch of sunspots that energized activity less than two
weeks ago has drifted around the edge of the Sun.  You can see the
effects in the falling daily sunspot numbers and solar flux.
Average daily sunspot number dropped a little over 63 points to
91.3.  At the same time, geomagnetic disturbance increased, so ideal
conditions with high sunspot activity and quiet geomagnetic
conditions are reversing.

On July 10 a coronal mass ejection from a day earlier hit Earth, and
caused a geomagnetic storm.  The same day it hit, the planetary A
index jumped to 47, and another coronal mass ejection began a
journey from the sun.  As a result, the planetary A index went back
up, this time to 48 on July 12.  All this as sunspot numbers and
solar flux dropped.

Solar activity is currently increasing, but only from some sunspots
that are drifting from view.  They may deliver an indirect hit to
Earth in the next couple of days.  The interplanetary magnetic
field, or IMF, is pointing south, which means our Earth is
vulnerable.  Currently the planetary A index for Friday through
Monday, July 15-18 is predicted to be 25, 25, 20 and 12.

Sunspot numbers and solar flux should reach a short term minimum
around July 16-19, and another maximum around August 2-5.  This is
based on the recent peak in activity, and the fact that the sun
rotates relative to earth about once every 27-28 days.

This time of year West Coast stations often see good propagation in
the evening to the west and southwest, to Hawaii, and down toward
Australia, where the season is now winter.  20 meters can be open
all night, with 15 and 17 meters showing good propagation through
the evening.  The East Coast of North America will see good 20 meter
propagation into the evening toward Europe, with the band often
staying open four or five hours later than it will about a month
from now.

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 July 7 through 13 were 149, 111, 126, 78, 68, 52
and 55 with a mean of 91.3. 10.7 cm flux was 124.9, 110.4, 106.6,
101.8, 93.3, 95.3 and 91.7, with a mean of 103.4. Estimated
planetary A indices were 8, 5, 19, 47, 23, 48 and 30 with a mean of
25.7.  Estimated mid-latitude A indices were 6, 5, 13, 28, 14, 17
and 20, with a mean of 14.7.


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