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ARRL Propagation Bulletin ARLP015 (2005)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 15, 2005
To all radio amateurs 

ARLP015 Propagation de K7RA

This week there was an insignificant rise in average daily sunspot
numbers and solar flux compared to the previous week. Average daily
sunspot numbers were up a little over one point to 40.6, and average
daily solar flux rose over four points to 86.9.

There was a rise in geomagnetic activity due to a solar wind stream
from a coronal hole. The planetary A index for April 12-14 was 30,
26 and 19. We have moved out of the solar wind, and the prediction
is for quieter conditions. The predicted planetary A index for April
15-18 is 12, 10, 8 and 5. Sunspot counts and daily solar flux
numbers are expected to stay about the same, perhaps declining
slightly after April 19.

I noticed on the web site for the Western Washington DX Club
( a number of links to presentations from past
club meetings, either on technical topics or DXpeditions. One of
interest to readers is a PDF of the K9LA talk on 160-meter
propagation at last summer's Northwest DX Convention. (It is on the
main page, and if you don't know how to open a PDF,
send me an email). This is a very interesting tutorial on several
aspects of 160-meter propagation, and examines the notion that this
band is better during the sunspot minimum.

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,

Sunspot numbers for April 7 through 13 were 49, 56, 43, 42, 17, 32
and 45 with a mean of 40.6. 10.7 cm flux was 87.8, 87.7, 88.4, 88.3,
87.5, 84.9 and 83.5, with a mean of 86.9. Estimated planetary A
indices were 8, 4, 4, 4, 10, 30 and 26 with a mean of 12.3.
Estimated mid-latitude A indices were 4, 2, 2, 2, 6, 23 and 18, with
a mean of 8.1.


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