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ARRL Propagation Bulletin ARLP030 (2004)

ARLP030 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 30  ARLP030
From Tad Cook, K7RA
Seattle, WA  July 23, 2004
To all radio amateurs 

ARLP030 Propagation de K7RA

Rising solar activity is in the news this week. Sunspot 652, a
really big one, is currently looking straight at Earth. We are also
experiencing effects from a coronal mass ejection from this spot.
Early Thursday, July 22 (actually Wednesday night in the Americas)
geomagnetic K indices were at 0 at all latitudes, even above the
Arctic Circle. The effects of the coronal mass ejection itself were
unimportant, but there was a strong solar wind behind it and the
interplanetary magnetic field pointed south, which makes Earth
vulnerable. By Thursday night K indices were at 5 and 6.

Average daily sunspot numbers this week over the week previous rose
more than 72 points. Average daily solar flux rose nearly 48 points.
When the daily sunspot number reached 176 on Monday, July 19, it was
the highest reading of this index since November 30, 2003. The solar
flux at 175.2 on July 20 was the highest flux value since November
24 of last year. Of course, this doesn't signal any sort of upward
trend in the solar cycle, but at this point there is still enough
variation to provide some excitement and interest.

The latest SEC prediction still shows the low point of the smoothed
sunspot cycle around December 2006 to January 2007. The January 2005
predicted smoothed sunspot number of 21 is two years prior to the
predicted cycle bottom, but December 2007 shows the smoothed sunspot
number rising back to 21. You can see this at the back of this
week's Preliminary Report and Forecast from Space Weather
Operations, on the web at, You will need Adobe
Reader to view it.

For July 23-26, Friday through Monday, the predicted planetary A
index is 25, 15, 10 and 10. Predicted solar flux for those same
dates is 170, 160, 160 and 150. For HF, we generally want sunspot
counts to be high for several days with stable geomagnetic
conditions. Often the two don't arrive together.

Carl Luetzelschwab, K9LA, wrote a great piece for the propagation
section of the ARRL Technical Information Service site titled
"Propagation Planning for DXpeditions." The information in this
article isn't just for folks planning expeditions to rare DXCC
countries, but has good information about HF propagation and
planning your ham radio activities. The link to his article is

Here is an interesting website: This is the Space Weather
Resources Page from the Rice Space Institute at Rice University in
Texas. This page has many interesting links for those interested in
space weather and its effects.

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service propagation web page at,

Sunspot numbers for July 15 through 21 were 146, 142, 165, 169, 176,
147 and 162 with a mean of 158.1. 10.7 cm flux was 145.7, 146.5,
149.2, 155.1, 170.2, 175.2 and 172.2, with a mean of 159.2.
Estimated planetary A indices were 9, 12, 24, 9, 9, 9 and 6, with a
mean of 11.1. Estimated mid-latitude A indices were 7, 8, 13, 6, 8,
6 and 5, with a mean of 7.6.


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