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The K7RA Solar Update


Solar activity perked up this week, with average daily sunspot numbers rising from 65.6 in the previous seven days to 120.9 in the April 16-22 period.

Average daily solar flux increased from 132.5 to 150.4 over the same period.

The day with the most geomagnetic activity was April 16, when the mid-latitude A index was 28, planetary A index was 43, and the high latitude college A index in Alaska was 57. These are high numbers!

Predicted solar flux for the near term is 135 and 130 on April 24-25, 125 on April 26 through May 1, 130 on May 2-5, 135 and 140 on May 6-7, 145 on May 8-9, 140 on May 10, 135 on May 11-16 and then a jump to 150 on May 17-18 before declining to 125 on May 23.

Predicted planetary A index is 8 and 12 on April 24-25, 8 on April 26-27, 10 on April 28, 8 on April 29 through May 2, 5 on May 3-5, 8 on May 6-8, 5 on May 9-11, then 8, 15, 20, 12, 8 and 12 on May 12-17, and 5 on May 18-19.

From April 16-22 there was one new sunspot region appearing each day, except for April 21 when there were two.

If you check the solar flux prediction archive at (click on “Download This File”) you can see how dramatically the prediction for the next few days changed recently. The forecasters pulled back on their estimates for higher solar flux.

F.K. Janda, OK1HH, sent his weekly geomagnetic prediction, and he sees quiet to active conditions April 24, active to disturbed April 25, quiet on April 26, quiet to active April 27, quiet to unsettled April 28, disturbed April 29, active to disturbed April 30 through May 1, quiet to active May 2, mostly quiet May 3-6, active to disturbed May 7-8, quiet to active May 9, mostly quiet May 10, quiet on May 11, active to disturbed May 12, disturbed May 13-14, quiet to active May 15, quiet to active May 16-18, and mostly quiet May 19-20.

OK1HH says that increases in solar wind are mostly unpredictable, but he expects increases on April 24, May 3-5, May 15-18, and May 20.

On Sunday, April 19 Jeff Hartley, N8II, of Shepherdstown, West Virginia wrote: “The high solar wind essentially closed 15 meters and up for a couple of days late last week except for South America. It is back to near normal now. I easily worked HS0ZCW on 12 meter SSB today at 1517Z and a few loud southern Europeans. Ten meters never really opened to Europe, but EA8DAZ was S9+20 db.’

On April 23, Jon Jones, N0JK, of Kansas wrote: “10 meters was good to the South Pacific the afternoon of April 23. FW5JJ was quite loud to the Midwest USA around 2200z on 28.029 MHz. I worked him with 50 W while parked from my mobile. K index was 0.

“Last Saturday, April 18, there was strong early season sporadic E on 6 meters. I worked W7GJ in Montana and KE8FD in Utah at about 2145z on 50 MHz via Es. K7TNT in Wyoming had a pipeline to CE2AWW for 2 hours. No copy on CE2AWW in Kansas. I had to work Saturday night shift, but saw many people spotted FK8CP via Es link to TEP that evening.”

I believe his ten meter mobile antenna is one of those shortened CB whips on the roof of his car.

For more information concerning radio propagation, see the ARRL Technical Information Service at For an explanation of the numbers used in this bulletin, see An archive of past propagation bulletins is at More good information and tutorials on propagation are at

Archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are at and . Click on “Download this file” to download the archive and view in spreadsheet format.

Monthly propagation charts between four USA regions and twelve overseas locations are at

Instructions for starting or ending email distribution of ARRL bulletins are at

Sunspot numbers for April 16 through 22 were 85, 93, 114, 142, 125, 153, and 134, with a mean of 120.9. 10.7 cm flux was 150.2, 149.6, 147.6, 151.7, 149.6, 153.8, and 150.3, with a mean of 150.4. Estimated planetary A indices were 43, 25, 13, 9, 10, 22, and 11, with a mean of 19. Estimated mid-latitude A indices were 28, 20, 10, 9, 9, 18, and 9, with a mean of 14.7.




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