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The K7RA Solar Update


This week we had a couple of brief sunspot appearances -- 991 and 992 -- but they were both from Solar 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).

Expect geomagnetic conditions to stabilize this weekend, but to again become active on May 2. Sunspot numbers for April 17-23 were 0, 0, 13, 12, 0, 13 and 13 with a mean of 7.3. The 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.

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 bulletin 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. Also check out his page on last fall's 10 meter sporadic-E season.

There was a tremendous response this week from readers wanting a copy of Ken Tapping's observations on the current sunspot minimum; more than 300 requests were received over the weekend. You can still get one e-mailed to you by sending a blank e-mail to Any e-mail sent to this address will get the same document.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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