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ARRL Propagation Bulletin ARLP019 (2015)

ARLP019 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 19  ARLP019
From Tad Cook, K7RA
Seattle, WA  May 8, 2015
To all radio amateurs 

ARLP019 Propagation de K7RA

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

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 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 . 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

On May 1, Bill Crowley, K1NIT wrote: "Yesterday afternoon about
1800Z, I was crawling around on 15 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 is not
hearing any 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 from here. 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 20m has been worthwhile for
working eastern Europe and Russia, as always, 17m has been less so,
15 has been downright poor, while 12 and 10 have hardly been worth
the effort of even checking. Mostly just the occasional sporadic-E
opening into the southern US and occasionally western Europe, but
very little F2.

"6 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
U.S., along with the first Es openings of the year, some of which
extended that TEP into the central and northern U.S. 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, with the 304a 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 were being reported, while stations along the
southern tier states in the U.S. 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, on
three separate days at local noon here, 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, long path, on two successive days. Two days
later, it was my turn; Willem heard my 90 watts 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, though 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; it's just that the Anomaly traverses water and regions with
very few hams along most all of its length, so few hams are around
to notice the openings."

Scott also sent an article on fractal analysis of sunspot numbers:

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 50W 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 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 on the other end is one of the people
responsible for the monster antennas shown here, which may give a
hint regarding antenna gain at the other end:

Yekta Gursel, KJ6DRO sent this video about the solar flare on May 5:

On the same subject, Rick Radke, W9WS sent this:

Also note this article:

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."

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service web page 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
. 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 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.


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