Sunspot numbers over the past two weeks began with a daily reading of 110 on April 23 and ended at 110 on May 6. In between, the sunspot number was just 13 on May 1, but the weekly averages were nearly the same, at 60.7 during the first week and 60.9 for the second.

Geomagnetic indices were high on May 6, at 23 for the planetary A index and 21 for the mid-latitude A index.

The reported mid-latitude A index on May 5 was an approximation, reported at 11, because the A index calculation is made up of eight 3-hour K index readings in 24 hours, but only two of the readings were available, both at the end of the UTC day. A similar but worse situation occurred with the high latitude college A index from Fairbanks, Alaska. No K index data from 1500 UTC May 4 through 1500 UTC May 5. You can see this at ftp://ftp.swpc.noaa.gov/pub/indices/DGD.txt in which any K index of -1 is either missing or not yet reported.

The latest prediction from NOAA/USAF shows improving conditions over the next week with solar flux at 150 on May 8-10, 155 on May 11, 150 on May 12-13, 145 on May 14-15, 130 on May 16, 125 on May 17-18, 120 on May 19, 115 on May 20-23, 110 on May 24-26, then up to 140 on June 8-9.

Predicted planetary A index is 5 on May 8-10, then 10 on May 11, 20 on May 12-13, 10 on May 14-15, then 8, 12, 20, 12 and 8 on May 16-20, 5 on May 21-25, 8 on May 26, 10 on May 27-28, 8 on May 29, and 5 on May 30 through June 7.

In last week’s bulletin we failed to report the update to our three month moving average of sunspot numbers. The latest three month average centered on March 2015 (including all sunspot numbers from February 1 through April 30) was 68.2. This follows the averages centered on August 2014 through February 2015 of 115.6, 108.4, 107, 104.7, 107.8, 98.2 and 78.1. The average peaked at 146.4 and 148.1 in February and March 2014.

A similar peak but on a different scale, using a 12-month smoothed reading of international sunspot numbers shows May 2014 as the peak. You can see this on page 15 at http://legacy-www.swpc.noaa.gov/weekly/pdf/prf2070.pdf. A similar table for 10.7 cm solar flux on the following page shows the peak at June 2014 in the same publication.

The weekly prediction for geomagnetic conditions from OK1HH shows quiet to active conditions for May 8-9, active to disturbed May 10, mostly quiet May 11, active to disturbed May 12, disturbed May 13-14, active to disturbed May 15, quiet to active May 16—18, quiet to unsettled May 19, quiet May 20-23, mostly quiet May 24, quiet to unsettled May 25, quiet May 26-27, mostly quiet May 28, quiet to unsettled May 29, quiet to active May 30, quiet to unsettled May 31, active to disturbed June 1, and mostly quiet June 2.

OK1HH believes that increases in solar wind are unpredictable, but expects solar wind to pick up on May 14-18, 20, 22, 30-31, and June 2-3.


On May 1, Bill Crowley, K1NIT, wrote: “Yesterday afternoon about 1800Z, I was crawling around on 15 meter CW when I came across T6T in Kabul, Afghanistan. This was the first time I had heard him with more than an S-2 signal, as he was usually buried in the noise. He passed out a report to an EA, and I gave him a call. To my surprise and delight, he came back with "NIT?" and we completed the contact. He was an honest 599, but with deep QSB that took him down to an S-5. Then I experienced the same situation with A45XR in Oman. And to make it even more amazing, both contacts were with my Force 12 C-4 Yagi pointed due west, because my rotor is on the fritz! Right after that, the band collapsed.”

Great report, Bill. And with his antenna pointed at 270 degrees, he worked stations that were toward 32.8 degrees (T6T) and 48.5 degrees (A45XR) short path.

Scott Bidstrup, TI3/W7RI, wrote, “As sunspot numbers decline, so have conditions on the HF bands here in the single-digit latitudes. Here in Costa Rica, the rainy season is just beginning, and with it, the atmospheric noise has been building, bringing a screeching halt to any significant activity on Top Band (160 meters), and severely limiting DX on 80 meters as it does every year at this time, and will through the northern summer. Jay, HP3AK, reports that he has not been hearing DX in the 80 meter window on his monster delta-loop array during morning gray line, for several days at a stretch. His newly-built rotatable ZL Special on 40, optimized for front-to-back, however, has been his DX lifeline, offering just enough noise immunity to enable DX on that band. His newly-installed Waller Flag antenna for noise rejection on 80 has been a big help, but it's no panacea for the raucous noise coming from the Intertropical Convergence Zone that challenges our low-band efforts here. I suspect the really high angle noise coming in from almost directly above is the reason why he's not seeing better results. It's been a big help with his power line noise, though.

“With the declining solar activity, the higher bands have lately been dismal here to say the least. While 20 meters has been worthwhile for working eastern Europe and Russia, as always, 17 meters has been less so. Fifteen meters has been downright poor, while 12 and 10 have hardly been worth the effort of even checking. There is just the occasional sporadic E opening into the southern US and western Europe, but very little F2.

“Six meters has also been in the doldrums with the solar activity way down, though a brief rise in the 304 angstrom UV index for a couple of weeks, combined with some coronal hole passages, brought about a few spectacular TEP openings into South America from the southern US, along with the first Es openings of the year. Some of these extended that TEP into the central and northern US states on a couple of days.

“Unfortunately, it didn't last all that long, and now we're back in the doldrums as I write this. The 304a is too low to support much 6 meter F2 propagation of any type, including the afternoon TEP that we had been seeing. As so often happens, the afternoon TEP has been going right over our heads here in Costa Rica, and few contacts with Central America are being reported, while stations along the southern tier states in the US were having a field day. One really good Es opening into the northern Caribbean enabled me to pick up HI8 for a new one, however.

“There was one truly spectacular exception to all this dismal news: during the heyday of that TEP activity, between April 21 and 24, an apparent chordal duct opened up to the east of us along the length of the Equatorial Anomaly, allowing Mike, TI5XP, and Phil, TI5/N5BEK, to both work Willem, DU7/PA0HIP, on long path, on two successive days. Two days later, it was my turn; Willem heard my 90 W into a vertical reasonably well, giving me a 419 report, but I was not able to complete the exchange, as a very high noise level on my end precluded me from copying him. Even so, his CW signal was clearly visible on my waterfall, even with my S5 noise level. The QSOs with Mike and Phil were with their antennas beaming 110 degrees and Willem reporting he was beaming towards the Sahara. This recurring activity leads me to suspect that chordal ducting along the Equatorial Anomaly is probably much more common than is generally assumed. Since the Anomaly traverses water, as well as land masses with very few hams, most of these openings go unnoticed.”

Scott also sent an article on fractal analysis of sunspot numbers: http://www.sciencedaily.com/releases/2015/04/150429113204.htm

Scott commented: “Here's an article that shows just how unexpectedly useful theoretical mathematics can turn out to be. A fractal analysis of sunspot numbers has revealed that there must be at least two mechanisms that generate the solar magnetic field that drives them, rather than the single mechanism that had always been assumed. The article is a bit "mathy" but the payload about the sunspot numbers is at the end.”

Carl, K9LA, forwarded a copy of a note he sent to N0JK about his 10 meter QSO with 9A9A reported in the last bulletin:

“VOACAP says the monthly median F2 region MUF at 1800 UTC between you and 9A would be around 23.8 MHz. That says the probability of a 28.4 MHz opening is around 9 percent. In other words, 10 meters would be expected to be available on a couple days of the month (30 times .09 = 2.7 days).

“The predicted signal strength for your 50 W is low, but my assumptions for your antenna gain and the 9A antenna gain are probably pessimistic (especially on his end).

“So, it very well could be that you just experienced the day-to-day variation of the F2 region - and it was good enough on a few days.”

Also, I noted that 9A9A is one of the people responsible for the monster antennas shown here, which may give a hint regarding antenna gain his end: http://www.qrz.com/db/9a1a


Yekta Gursel, KJ6DRO, sent this video about the solar flare on May 5: http://www.space.com/29326-biggest-sun-solar-flare-2015-video.html

On the same subject, Rick Radke, W9WS sent this: http://mashable.com/2015/05/06/sun-unleashes-huge-solar-flare/

Also note this article: http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2015/05/06/sun-ejects-intense-x-class-flare-signaling-increase-in-solar-activity/

On May 7 at 2338 UTC the Australian Space Forecast Centre issued a geomagnetic disturbance warning. “A solar prominence (disappearing solar filament) erupted from the geoeffective zone of the solar disk during 15 UT on 6 May. A weak partial halo CME was associated with this event. A minor geomagnetic storm is possible if the CME impacts Earth on 10 May.”


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/.

Archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are at http://www.filedropper.com/filemanager/public.php?service=files&t=326dd41340bab1066cf91d13df36b8fd and http://www.filedropper.com/filemanager/public.php?service=files&t=be2a0a69fb6392907dc3d9a017dcace1. 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 http://arrl.org/propagation.

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

Sunspot numbers for April 30 through May 6 were 27, 13, 25, 67, 85, 99, and 110, with a mean of 60.9. 10.7 cm flux was 101.8, 99.9, 105.7, 111.1, 125, 127.8, and 136.2, with a mean of 115.4. Estimated planetary A indices were 5, 6, 9, 8, 6, 5, and 23, with a mean of 8.9. Estimated mid-latitude A indices were 4, 6, 9, 7, 7, 11, and 21, with a mean of 9.3.