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ARRL Propagation Bulletin ARLP009 (2005)

ARLP009 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 9  ARLP009
From Tad Cook, K7RA
Seattle, WA  March 4, 2005
To all radio amateurs 

ARLP009 Propagation de K7RA

This week saw a quiet sun, which will be a frequent observation over
the next few years. The average daily sunspot number was down nearly
31 points to 14.9, and average daily solar flux was off 21 points to
76.3. Planetary geomagnetic activity was down just slightly, and mid
latitude activity was just about the same as the previous week.

Unsettled to active geomagnetic conditions were expected over last
weekend (February 26-27) due to a strong solar wind, but the only
day with even slightly unsettled conditions was Monday, the last day
of February, and any activity was brief. All week the Interplanetary
Magnetic Field (IMF) pointed north, which shielded the earth from
any solar wind. The sun was blank most of the week, with only small
sunspot 739 transiting across the visible solar disk.

Check for a review of
the IMF and how it can affect geomagnetic stability. Also check a
site I haven't seen before,
This was submitted by Jon Jones, N0JK.

Over the next week expect a rising sunspot count and solar flux,
with flux values peaking above 100 around March 11-14. March 6-9
could see some unsettled to active geomagnetic conditions based on
activity during the previous solar rotation.

This weekend is the ARRL International DX SSB Contest. Don't expect
great conditions like when the sunspot cycle was higher, but at
least we are moving toward the spring equinox and the geomagnetic
conditions should be quiet.

Last week's bulletin stimulated a couple of questions about
resources for understanding sporadic-E propagation. Go to the URL
for the ARRL TIS propagation page mentioned a couple of paragraphs
down, and check out the two-part "Sporadic-E - A Mystery Solved?"
articles in PDF files. You will need an ARRL membership to log in to
the web site to read this. There are other articles on other
propagation topics on the same page that are available for anyone to

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 February 24 through March 2 were 17, 15, 27, 12,
11, 11 and 11 with a mean of 14.9. 10.7 cm flux was 80.3, 78.2,
76.6, 75.8, 75, 73.7 and 74.6, with a mean of 76.3. Estimated
planetary A indices were 5, 9, 9, 8, 12, 11 and 12 with a mean of
9.4. Estimated mid-latitude A indices were 4, 9, 9, 6, 8, 10 and 8,
with a mean of 6.6.


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