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26 April, 2008
ARLP018
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, http://pluto.space.swri.edu/image/glossary/IMF.html.
Expect geomagnetic conditions to stabilize this weekend, but againbecome 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, http://tinyurl.com/697hho, 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,
http://www.swotrc.net/ProbabilityEs.pdf. Also check out his page on last Fall's 10 meter sporadic-E season at,
http://www.swotrc.net/10MeterPropNet.htm.
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, SunspotMin@gmail.com.
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, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL Technical Information Service Web page at,
http://www.arrl.org/tis/info/propagation.html.
For a detailed explanation of the numbers used in this bulletin see, http://www.arrl.org/tis/info/k9la-prop.html.
An archive of pastpropagation bulletins is at http://www.arrl.org/w1aw/prop/.
Monthlypropagation charts between four USA regions and twelve overseaslocations are at http://www.arrl.org/qst/propcharts/.
Instructions for starting or ending email distribution of this bulletin are at http://www.arrl.org/w1aw.html#email.
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 6.1.
Source: The
American Radio Relay League
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