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ARRL Propagation Bulletin ARLP018 (2008)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  April 25, 2008
To all radio amateurs 

ARLP018 Propagation de K7RA

This week we had a couple of brief sunspot appearances, 991 and 992,
but they were both from old Cycle 23, and their emergence was
fleeting.  On Wednesday, April 23 the planetary A index rose to 32
due to a solar wind and south-pointing Interplanetary Magnetic Field
(IMF).  An explanation of IMF and the significance of it pointing
south are at,

Expect geomagnetic conditions to stabilize this weekend, but again
become active on May 2.

Walt Knodle, W7VS of Bend, Oregon pointed out politely that the line
"The only previous Cycle 24 activity was close to the solar equator"
from last week's Propagation Forecast Bulletin ARLP017 was
incorrect.  He sent a magnetogram link,,
showing that in early January spot 981 was in fact high-latitude.

The Spring/Summer E-layer propagation season is beginning, and Art
Jackson, KA5DWI, has an interesting analysis that looks quite
useful.  You can get it from,  Also check out his page on
last Fall's 10 meter sporadic-E season at,

There was a tremendous response this week from readers wanting a
copy of Ken Tapping's observations on the current sunspot minimum,
with over 300 requests over the weekend.  You can still get one
emailed to you by sending a blank email to,
Any email sent to this address will get the same document.

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service Web page at,  For a detailed
explanation of the numbers used in this bulletin see,  An archive of past
propagation bulletins is at  Monthly
propagation charts between four USA regions and twelve overseas
locations are at

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for April 17 through 23 were 0, 0, 13, 12, 0, 13,
and 13 with a mean of 7.3.  10.7 cm flux was 69.2, 70.2, 71, 70.8,
70.9, 71.3, and 70.7 with a mean of 70.6.  Estimated planetary A
indices were 8, 6, 5, 4, 4, 5 and 32 with a mean of 9.1.  Estimated
mid-latitude A indices were 7, 5, 6, 1, 3, 4 and 17, with a mean of


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