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ARRL Propagation Bulletin ARLP023 (2010)

ARLP023 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 23  ARLP023
From Tad Cook, K7RA
Seattle, WA  June 11, 2010
To all radio amateurs 

ARLP023 Propagation de K7RA

With calmer solar activity, geomagnetic conditions were stable this
week.  Average daily sunspot numbers were down 7.6 points to 17.7,
and average daily solar flux dropped two points to 71.  Average
planetary A index declined 6.4 points to 7.9, and mid-latitude A
index dropped 2.7 points to 6.4.

Four new sunspot groups emerged this week.  1077 made a brief
appearance on June 5, and 1078 on June 8-10.  The area of 1078 grew
rapidly, from 80 millionths of a solar hemisphere to 180 on June 9
and 200 on June 10.  On June 9 sunspot group 1079 appeared, at 10
millionths of a solar hemisphere, and on June 10 sunspot group 1080
emerged, also at 10 millionths of a solar hemisphere.  Old sunspot
group 1072, last seen on May 28, might return over June 11-13.

All current sunspot groups are in the far southwest of the solar
disc, and should disappear soon as they move across the horizon.

Just ten more days until the Summer Solstice, on June 21 at 1128z,
after which the days become shorter.  ARRL Field Day is on the sixth
and seventh day of Summer, June 26 and 27.

The latest NOAA/USAF forecast has the planetary A index at 5 on June
11-15, 10 on June 16-17, back for 5 on June 18-24, 12 on June 25,
and 15 on June 26-27 (Field Day).  Two weeks from now is a bit far
off for an accurate forecast, but an A index of 15 would mean
somewhat unsettled conditions.  Solar flux predictions are 72 on
June 11-12, 70 on June 13-17, 72 on June 18, 75 on June 19-26, and
72 on June 27 through July 1.

Geophysical Institute Prague predicts quiet conditions on June
11-14, unsettled June 15, unsettled to active June 16, and unsettled
June 17.

Of course, we want sunspot numbers and solar flux high, and A index
low for good HF propagation.

Vic Morris, AH6WX lives in the northwest area of the island of
Hawaii, in Waikoloa.  He has noticed the low solar flux values of

He writes, "Does anyone have an explanation for the marked decrease
in solar flux since February?  At one point we peaked at 94,
seemingly indicating the long overdue increase expected for Cycle
24?  But the June 6 reading of 68 is I believe the lowest value of
2010 to date."

Yes Vic, the values are lower, and they don't seem to track very
well with sunspot numbers.  Normally when sunspot numbers increase,
so does solar flux, a measurement of 2.8 GHz energy received from
the Sun.  But a glance at the web site
shows the generally declining flux.

Vic is correct about higher solar flux earlier this year.  It was 90
or above on January 11-14 and again February 7-13, and March 12-13.
It was below 70 on May 13, and May 16-20, and again June 6-7.  It
was exactly 68.0 for the noon reading on June 6, and that was the
lowest solar flux recorded this year, although the morning reading
that day (morning and afternoon readings don't count for the
official flux value, which is taken at local noon) was just 67.7.

I don't know why this is happening, although there is some seasonal
variation.  Due to the variation in distance from the Sun, the
observed flux values are lower at this time of the year.  On June 6
when solar flux was only 68, the adjusted value (to compensate for
the variation in distance) was 70.  Of course we care about the
actual measured value, since that is what affects the ionosphere,
but the adjusted value is a more accurate reading of actual activity
from the Sun.

If we look back at the readings earlier this year, we see the
opposite effect from adjusted values.  On January 12-13 the observed
solar flux was 93.3 and 90.5, but the adjusted values were 90.2 and
87.5.  Not sure why adjusted values would ever be lower, but I'll
check on that.

Vic continues, "I can see the effects of the low solar flux on
over-the-pole 20 meter propagation to Europe here in the evening.
There were quite a few good openings to Europe earlier in the spring
when flux values were well into the 80s. These have mostly
disappeared the past 2-3 weeks. Note I do not have a beam or tower
at this point, just a vertical antenna. I've managed about 150 DXCC
countries here over about 6 years by doing a lot of listening."

Brian Webb, KD6NRP sent an impressive list of countries worked in
the past few years via PSK31, a very powerful digital mode that
works well with weak signals.  He runs under 100 watts and uses low
antennas (12 feet high, although he didn't say what kind) from his
50x50 foot back yard.

Pat Rose, W5OZI in Junction, Texas (EM00cl) reports that on June 3
at 2238z he worked JE1BMJ on 6 meters, a distance of 10,315 km.
Both signal reports were 579, but very soon it was over.

The day prior, Rich Molinski, WB2KWF in Smithfield, Virginia
observed some great 2 meter propagation.  He is in FM16, and worked
EM25 (Eastern Oklahoma) on 2 meters at 2230z.  He also worked K0FX
(Colorado) and W0FY (Missouri).  He said also that 6 meters was
great on June 4.

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

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 June 3 through 9 were 17, 18, 25, 12, 12, 12,
and 28 with a mean of 17.7. 10.7 cm flux was 74.6, 71.9, 70.3, 68,
68.5, 71.9 and 71.5 with a mean of 71. Estimated planetary A indices
were 13, 16, 6, 7, 6, 3 and 4 with a mean of 7.9. Estimated
mid-latitude A indices were 13, 11, 6, 5, 4, 3 and 3 with a mean of


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