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ARRL Propagation Bulletin ARLP021 (2017)

ARLP021 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 21  ARLP021
From Tad Cook, K7RA
Seattle, WA  May 26, 2017
To all radio amateurs 

ARLP021 Propagation de K7RA

At 2344 UTC on May 23, the Australian Space Forecast Centre issued a
geomagnetic disturbance warning for May 26 and 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:
Average daily sunspot number for the reporting week (May 18 to 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
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 to 28, 75 on May 29 to June 1,
72 on June 2 and 3, 70 on June 4 to 8, 72 on June 9 to 11, 74 on
June 12 to 18, 76 on June 19 to 23, 74 on June 24 and 25 (Field Day
weekend), 72 on June 26 to 30, then 70 on July 1 to 5 and 72 on July
6 to 8.
Predicted planetary A index is 12 on May 26, 20 on May 27, 10 and 8
on May 28 and 29, 5 on May 30 to June 9, 10 and 12 on June 10 and
11, 5 on June 12 and 13, then 8, 10 and 20 on June 14 to 16, 12 on
June 17 and 18, 8 on June 19, 5 on June 20 to July 6 and 8 on July 7
and 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 and 25) looks good. On June 23 to 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 .
Early Thursday I was attempting to discern the polarity of sunspots
at 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, 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
"Geomagnetic activity forecast for the period May 26 to June 21,
Geomagnetic field will be: 
Quiet on June 10, 
Mostly quiet on May 31, June 11, 
Quiet to unsettled May 26 and 27, 30, June 3, 6 to 8, 14, 19 
Quiet to active on May 28 and 29, June 4 and 5, 15, 20 
Active to disturbed on June (1 and 2, 9,) 12 and 13, 16 and 18 
Amplifications of the solar wind from coronal holes are expected on
May (30,) June (5 and 6,) 12 to 14, 16 to 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
actually 5:00 PM Friday, here on the West Coast.
See 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:
Here is the homepage for Etienne Pariat, one of the researchers:
On Thursday evening, West Coast time I noticed on
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.
For more information concerning radio propagation, see the ARRL
Technical Information Service at For an explanation of
numbers used in this bulletin, see
An archive of past propagation bulletins is at More good
information and tutorials on propagation are at
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 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.


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