At 2344 UTC on May 23, the Australian Space Forecast Centre issued a geomagnetic disturbance warning for May 26-27. On May 26, they predict a minor to major storm warning and on May 27 a minor storm. These are due to a “partial halo coronal mass ejection.”

Dr. Skov has a new space weather video: https://www.youtube.com/watch?v=mlTZTcplsQU


Average daily sunspot number for the reporting week (May 18-24) increased from 3.4 to 31.7. The previous week had five days of zero sunspots. There were no zero sunspot days this week, so the average daily sunspot number is much higher.

Over the same two weeks, average daily solar flux rose from 70.5 to 74.1.

Average daily planetary A index rose from 8.3 to 11 and average mid-latitude A index rose from 9.4 to 11.7.

Predicted solar flux is 78 on May 26-28, 75 on May 29 to June 1, 72 on June 2-3, 70 on June 4-8, 72 on June 9-11, 74 on June 12-18, 76 on June 19-23, 74 on June 24-25 (Field Day weekend), 72 on June 26-30, then 70 on July 1-5 and 72 on July 6-8.

Predicted planetary A index is 12 on May 26, 20 on May 27, 10 and 8 on May 28-29, 5 on May 30 to June 9, 10 and 12 on June 10-11, 5 on June 12-13, then 8, 10 and 20 on June 14-16, 12 on June 17-18, 8 on June 19, 5 on June 20 to July 6 and 8 on July 7-8.

ARRL Field Day is only four weeks away! We get 45-day predictions for solar flux and planetary A index, and the prediction for Field Day weekend (June 24-25) looks good. On June 23-25 (including the previous Friday) predicted planetary A index is 5 (good) and solar flux is 76 on Friday and 74 on Saturday and Sunday (not bad).

The 45-day forecast is updated daily, usually after 2100 UTC at ftp://ftp.swpc.noaa.gov/pub/forecasts/45DF/ .

Early Thursday, I was attempting to discern the polarity of sunspots at http://bit.ly/2qpMUxb and noticed that sunspot groups 12659 and 12660 showed opposite polarity (one had black on the leading edge while the other had black on the trailing edge). Thinking that one of these may be from Solar Cycle 24, while the other may be from Cycle 25, I sent a message to Carl Luetzelschwab, K9LA, for a sanity check.

Carl pointed out they are both from Cycle 24, and the opposite polarity is due to one being in the northern hemisphere and the other in the southern hemisphere. I had forgotten about sunspot groups in opposite hemispheres should have opposite polarity.

Carl also wrote, "If either was from Cycle 25, it would be at a higher latitude (above 20 degrees or so). And it would be of opposite polarity as regions in the same hemisphere."

F.K. Janda, OK1HH of the Czech Propagation Interest Group sent this:

Geomagnetic activity forecast for the period May 26-June 21, 2017

Geomagnetic field will be:
Quiet on June 10,
Mostly quiet on May 31, June 11,
Quiet to unsettled May 26-27, 30, June 3, 6-8, 14, 19
Quiet to active on May 28-29, June 4-5, 15, 20
Active to disturbed on June (1-2, 9,) 12-13, 16-18

Amplifications of the solar wind from coronal holes are expected on May (30,) June (5-6,) 12-14, 16-18

Remark:
- Parenthesis means lower probability of activity enhancement and/or lower reliability of prediction.”


This weekend is the CW portion of the CQ World-Wide WPX contest, from 0000 UTC Saturday, May 27 to 2359 UTC Sunday, May 28. You may operate no more than 36 of the 48 hours. Note 0000 UTC Saturday is 5:00 PM Friday, here on the West Coast. See http://www.cqwpx.com/rules.htm for rules.


Thanks to several readers (including most recently, Russ Ward, W4NI) who tipped us about using 3D numerical models to predict eruptive solar events: http://bit.ly/2qpykFS.

Here is the homepage for Etienne Pariat, one of the researchers: http://bit.ly/2r2211C

On Thursday evening, West Coast time I noticed on DXmaps.com sporadic-E openings on 10 meters all over the Western USA, and more extensively, 6 meters, from the Midwest to the West and West Coast.

Interesting research on variations in sunspot counts in flaring and non-flaring active regions. Note that all the references to ARs in this article refer to Active Regions. https://arxiv.org/pdf/1705.09065.pdf


For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of 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 18 through 24, 2017 were 24, 24, 22, 35, 55, 47, and 15, with a mean of 31.7. 10.7 cm flux was 72.2, 72.3, 72.4, 73.5, 74.4, 76, and 77.9, with a mean of 74.1. Estimated planetary A indices were 11, 11, 24, 9, 10, 8, and 4, with a mean of 11. Estimated mid-latitude A indices were 15, 13, 23, 10, 9, 8, and 4, with a mean of 11.7.