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The K7RA Solar Update


There was an upward bump in recent solar activity, with average daily sunspot number for the April 7-13 period at 32 (compared to 19.1 for the previous seven days) and average daily solar flux rising 23 points to 106.1.

Note that what we are seeing now is the occasional uptick in solar activity as the Sun continues its decline to solar minimum, perhaps sometime around 2020.

Average daily planetary A index rose three points to 12.4, and average daily mid-latitude A index from 7.6 to 8.3.

For the near term, predicted solar flux is 110 on April 15-17, 105 on April 18-19, 95 on April 20—22, 100 on April 23, 95 on April 24-29, 90 on April 30 through May 3, then 95, 100, 105, and 110 on May 4-7, 112 on May 8-13, and 115 on May 14-17. Solar flux then drops below 100 on May 21 and beyond.

Predicted planetary A index is 12 on April 15, 8 on April 16-18, 12 on April 19, 8 on April 20, 5 on April 21-22, 12 on April 23, 10 on April 24-25, 8 on April 26, 5 on April 27-28, then 20, 15 and 8 on April 29 through May 1, 5 on May 2-3, then 12 and 8 on May 4-5, 5 on May 6-7, 8 on May 8-9, then 18, 30 and 10 on May 10-12, then 5 on May 13-16 and 8 on May 17-18.

Also on the subject of geomagnetism, we have two predictions from Prague. The first from the Institute of Geophysics of the Academy of Sciences of the Czech Republic. Tomas Beyer predicts for the short term:

Geomagnetic activity forecast for the period April 15-21, 2016

Quiet:  Apr 19-21
Unsettled: Apr 15-18
Active:  possible but unlikely Apr 17-18

Geomagnetic activity summary:

Maximum of geomagnetic activity has been recorded at Apr 12-13 when the local K-index reached K=5. The active conditions continued till morning Apr 14, then turned to unsettled.

Next week, we expect at most quiet to unsettled conditions only with possible active episode between Apr 17-18. Nevertheless, it may be only an isolated event. Then, we expect return of quiet to unsettled level.

From Petr Kolman, OK1MGW, of the Czech Propagation Interest Group, he predicts:

Geomagnetic activity forecast for the period April 15-May 11, 2016

Geomagnetic field will be:
Quiet on April 21-22, May 6-7
Mostly quiet on  April 17-18, 27-28, May 1-3, 8
Quiet to unsettled on  April 15-16, 19-20, 25-26, May 11
Quiet to active on April 23-24, 29-30, May 4-5, 9-10
Active to disturbed on May (9-10)

Amplifications of the solar wind from coronal holes are expected on April 18-20, 23-24, 28-30, May 4-5, 8-11

Remarks: Parenthesis means lower probability of activity enhancement.

Recently KL7JT asked a question which we forwarded to K9LA. Here is a link to the exchange, which includes links to the images referenced. Just click Download This File at each link.

Here is an update on the NASA STEREO mission:

And this link is to the STEREO tool itself:

Bill Liles, NQ6Z, wrote about a QSO Today podcast (Number 081) he heard:

"I am curious about one comment you made. You were asked about effect from solar or lunar eclipse and you answered ‘no.’

“I agree with that answer re lunar eclipse. I am wondering about the reason for the answer with respect to solar eclipse. During the time of the eclipse over a patch of the ionosphere, which granted is only a few minutes, the Sun's radiation is blocked so one should see recombination in the D layer and thus it will not be as absorptive as during normal daytime. Thus MF and low HF freqs should experience nighttime propagation characteristics.

“This effect, as far as I have found, was first observed in 1912. Appleton also used this effect in the 1929s to help answer the question of what causes the ionization by the Sun, particles or electromagnetic waves.

“Solar eclipse effects have been the subject of many scholarly reports and a few books using real data.

“Thus my curiosity as to why your answer was ‘no?’ Were you meaning on a more global scale? As it seems true on a local scale.

“BTW, ARRL and Scientific American did a study on this effect in the 1920s and one comment was that 75 meters behaved as if it was nighttime."

The answer?  I was wrong.  In response, Bill sent a pdf about effects on radio from a solar eclipse in 1999, which you can download here:

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

My own archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format at and .

Click on “Download this file” to download the archive, and ignore the security warning about file format. Pop-up blockers may suppress the download.

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 7 through 13 were 26, 27, 29, 26, 41, 34, and 41, with a mean of 32. 10.7 cm flux was 92.3, 98.3, 105.5, 110.6, 116.6, 111.3, and 108.2, with a mean of 106.1. Estimated planetary A indices were 17, 9, 3, 7, 6, 19, and 26, with a mean of 12.4. Estimated mid-latitude A indices were 10, 6, 3, 6, 5, 12, and 16, with a mean of 8.3.




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