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ARRL Propagation Bulletin ARLP028 (2012)

ARLP028 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7RA
Seattle, WA  July 13, 2012
To all radio amateurs 

ARLP028 Propagation de K7RA

Solar activity rose moderately this week.  Average daily sunspot
numbers were up nearly 3 points to 120.9, and average daily solar
flux rose over 28 points to 166.8.  There was quite a bit of
geomagnetic activity, the most happening on July 9, when the
mid-latitude A index reached 29, planetary A index was 30, and
Alaska's college A index was 60.  That day I stopped in to visit
K7SS on my way back from a trip to Oregon, and a check of the bands
showed HF conditions were quite difficult.
Sunspot group 1520 was directly facing Earth on July 12 at 1653 UTC
when it spewed out an X.14 class solar flare.  We've seen flares off
to one side or another that had limited effect, but this one was
aimed straight at us.  There was an immediate SID (Sudden
Ionospheric Disturbance) event, and the resulting CME should reach
Earth some time around 1020 UTC Saturday, July 14.  This could be
bad news for operators in the IARU HF World Championship and other
operating events this weekend.  The accuracy of the 1020 UTC impact
estimate is plus or minus 7 hours.  The 24-hour contest begins at
1200 UTC Saturday.  See
for details.
The latest prediction shows planetary A index at 8, 18 and 15 on
July 13-15, then 5 on July 16-26, then 20 on July 27-29, 10 on July
30-31, 15 on August 1-2, 10 on August 3-4, 8 on August 5, and 5 on
August 6-22.
Predicted solar flux is 165 on July 13-15, then 160, 145, 130, and
120, on July 16-19, 105 on July 20-21, then 115, 120, 130, 140, 145
and 150 on July 22-27, and 165 on July 28 through August 2, 160 on
August 3-4, then 165, 155, and 150 on August 5-7, and 145 on August
If you check
and compare the July 11 and July 12 predictions, you can see a big
difference between the forecast in this bulletin (July 12) and the
one presented in this week's ARRL Letter, based on the July 11
Over the past week, four new sunspot groups appeared.  On July 7,
group 1520 was new and on July 8, older group 1517 (visible since
July 1) disappeared.  On July 9 group 1513 (visible since June 26)
was gone and 1521 was new.  On July 10, group 1515 (visible since
June 27) disappeared, and on July 11 group 1518 (around since July
4) was gone.  On June 12, two new groups, 1522 and 1523 appeared.
Petr Kolman, OK1MGW, again provides us with the Czech Propagation
Interest Group geomagnetic activity forecast.  Expect unsettled to
active conditions on July 13-15, mostly quiet July 16-18, quiet to
unsettled July 19-21.
You can follow progress of any geomagnetic disturbance this weekend
by checking and  Note the last site is available
in Dutch, French and German by selecting your language of choice in
the drop-down on upper right.
We received even more email about the old BC-458 SSB conversion,
including some corrections to the correction in the last bulletin.
We won't cover the subject any longer in this bulletin, but the
original March 1956 QST article by W2EWL is a treat to look at.  If
you are an ARRL member, you can find it in the QST archive by
logging into your account at and then going to  Just enter
"W2EWL" in the Author Call field, and March 1956 for the month and
year.  There you can download a 1.6 MB pdf of the article.
Walt Knodle, W7VS of Bend, Oregon sent along an article titled "MRI
of the Sun's Interior Motions Challenges Existing Explanations for
Sunspots".  Read it at
You can read articles about the most recent solar flare at and
Jon Jones, N0JK sent a message about the big recent 6 meter opening
and notes it was June 29, not June 30.  He says, "In Kansas, we were
at the edge of it.  N0LL worked MM0AMW at 1219 UTC followed by
LA7HJA at 1545 UTC.  I logged JW7QIA at 1642 UTC.  I was running 100
w and a 2 element Yagi portable for the contact with Peter.  He was
using a stack of two 5 el Yagis.  I heard him for about 5 minutes.
The VE4SPT/b EO26 was 599 at the same time."

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 at  For an explanation of
the numbers used in this bulletin, see  An archive of
past propagation bulletins is at  Find more good
information and tutorials on propagation 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 July 5 through 11 were 122, 131, 127, 113, 137,
122, and 94, with a mean of 120.9.  10.7 cm flux was 164.6, 157.7,
158.4, 177.7, 173.8, 173.4 and 161.7, with a mean of 166.8.
Estimated planetary A indices were 14, 16, 8, 13 30, 13, and 10,
with a mean of 14.9.  Estimated mid-latitude A indices were 13, 14,
8, 15, 29, 15, and 10, with a mean of 14.9.


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