There was a whopper of a geomagnetic storm on Mother’s Day, May 8, when the planetary A index reached 70. In Alaska, the college A index was 117. Aurora was visible in North America well south of the northern tier states.

Average daily sunspot number dropped 15.6 points to 59.1 over the past week, and average daily solar flux declined 3.1 points to 88.8.

Average daily planetary A index over the same period doubled from 11.3 to 22.6, and average daily mid-latitude A index rose 3.9 points to 14.6.

The latest prediction has planetary A index at 5 on May 13-14, then 8, 15, 12, 6, 5, 15 and 12 on May 15-21, 5 on May 22-23, 10 on May 24, 5 on May  25-27, then 10, 25 and 10 on May 28-30, 5 on May 31 through June 1, 12 on June 2-3, then 30, 32, 25, 15 and 8 on June 4-8, and 5 on June 9-10. Planetary A index then rises to 25 on June 25, but that is a long way off.

Predicted solar flux is 95 and 97 on May 13-14, 100 on May 15-16, then 95, 93, 90 and 85 on May 17-20, 82 on May 21-22, 85 on May 23-25, 90 on May 26-30, 88 on May 31 through June 2, 85 on June 3-6, 90 on June 7-9, 95 on June 10-11, then 90 and 85 on June 12-13, 82 on June 14-18, and 85 on June 19.

Petr Kolman, OK1MGW, of the Czech Propagation Interest Group says the geomagnetic field will be:

Quiet on May 16-17, 25-26
Mostly quiet on May 15, 22-24, 31, June 7-8
Quiet to unsettled on May 13-14, 18, 21, 27, 30
Quiet to active on May 19-20, 28-29, June 1-2, 3, 6
Active to disturbed on May (28), June 4-5

Increases in solar wind from coronal holes are expected on May 19-21, 28-29, June 1-6

Parenthesis means lower probability of activity enhancement.

We missed it last week, but here is the latest update on our 3-month moving average. According to our numbers, cycle 24 peaked with a sunspot number of 148.2 in the three months centered on March 2014.

Beginning with the 3 months centered on January, 2015, the 3-month moving average of daily sunspot numbers was 98.2, 78.1, 68.2, 72.4, 77.7, 76.3, 69.1, 67.5, 64.5, 64.6, 58.5, 55.4, 53.5, 49 and 45.3. The numbers reflect the steady decline of solar cycle 24.

According to http://1.usa.gov/1HOVlDP it looks like the next solar minima should be in 2019. These are international sunspot numbers, but the sunspot numbers we report in this bulletin are from the NOAA Space Environment Service Center, ftp://ftp.swpc.noaa.gov/pub/indices/DSD.txt .

David Moore sent this piece from Science Daily about solar wind:

https://www.sciencedaily.com/releases/2016/05/160511102655.htm

Now here is a surprising and counter-intuitive assertion. http://bit.ly/1rJxxki claims “When sunspots are minimal, the solar magnetic field is at a maximum.”

As mentioned in last week's bulletin, Carl, K9LA, offers the W6ELProp installation file, if you have trouble downloading it from www.qsl.net/w6elprop.

Note that the latest version of W6ELProp is Version 2.70, which was in the 2002 time frame. Thus it is likely that Shel, W6EL, never checked it out with newer operating systems like Vista and Windows 7, 8 and 10. Shel, W6EL, became a Silent Key in April 2015, and as far as Carl is aware the source code for W6ELProp was never released to anyone.

If anyone has successfully installed W6ELProp on a PC using Vista or Windows 7, 8 or 10, Carl would like to hear from you. Carl can be reached at k9la@arrl.net.

Actually, I have run it successfully on Windows 7 and 10, but Carl pointed out that the Maps feature doesn’t work.

The Solar Plotting Utility mentioned in past bulletin doesn’t run on Windows 7 or 10, but that is easily solved by running Windows XP as a virtual machine within the newer Windows versions.

In Windows 10 it is also possible to run older programs in Compatibility Mode.



For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of the numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation. More good information and tutorials on propagation are at http://k9la.us/.

Monthly propagation charts between four USA regions and twelve overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins.

Sunspot numbers for May 5 through May 11 were 55, 56, 51, 42, 68, 70, and 72, with a mean of 59.1. 10.7 cm flux was 87.1, 89.6, 88, 85.6, 88.5, 88.7, and 93.9, with a mean of 88.8. Estimated planetary A indices were 8, 15, 10, 70, 33, 16, and 6, with a mean of 22.6. Estimated mid-latitude A indices were 7, 12, 9, 32, 21, 15, and 6, with a mean of 14.6.