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ARRL Propagation Bulletin ARLP005 (2005)

ARLP005 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 5  ARLP005
From Tad Cook, K7RA
Seattle, WA  February 4, 2005
To all radio amateurs 

ARLP005 Propagation de K7RA

Average daily sunspot numbers were down this week by nearly 17
points (our reporting week runs from Thursday through the following
Wednesday for the timing of this bulletin). Over the same days the
average daily solar flux was also down nearly 17 points. The daily
geomagnetic indices showed much greater stability, with all of the K
and A indices down when compared with the previous seven days.

Look for quiet geomagnetic conditions over the next few days, with
the February 4-6 (Friday through Sunday) planetary A index around 8,
5 and 5. The A index is expected to rise again after this weekend
probably due to the return of sunspot 720, which caused so much
recent activity. It returns into view on its 27.5 day rotation, and
the planetary A index prediction for February 7-9 is 15, 25 and 15.

Sunspot numbers and solar flux should also rise, with solar flux
values rising above 100 after February 5, staying relatively high
(for this point in the declining sunspot cycle) at 130 or above
around February 7 and continuing for about a week.

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

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

Sunspot numbers for January 27 through February 2 were 43, 43, 30,
38, 49, 27 and 28 with a mean of 36.9. 10.7 cm flux was 86.9, 84.9,
86.4, 85.5, 86.2, 83.7 and 81.8, with a mean of 85.1. Estimated
planetary A indices were 3, 6, 20, 16, 19, 6 and 8 with a mean of
11.1. Estimated mid-latitude A indices were 2, 5, 16, 10, 15, 4 and
7, with a mean of 8.4.


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