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ARRL Propagation Bulletin ARLP016 (2012)

ARLP016 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 16  ARLP016
From Tad Cook, K7RA
Seattle, WA  April 20, 2012
To all radio amateurs 

ARLP016 Propagation de K7RA

As promised in the ARRL Letter, this week's bulletin features a
report on recent solar activity and solar cycle progression from
Carl Leuetzelschwab, K9LA.

Solar flux and sunspot numbers reached a short term low on April
8-11, but now are rising again.  For the past week, April 12-18,
average daily sunspot numbers more than doubled compared to the
previous seven days, rising more than 39 points to 71.7.  Average
daily solar flux increased from 95.9 to 105.1.  On April 19, the day
following this period, the daily sunspot number rose dramatically
from 96 to 122, and so did solar flux values, from 121.5 to 137.8

Since April 10, eleven new sunspot groups emerged.  One each on
April 10-13, two on April 14, one on April 16 two on April 17 and
one each on April 18-19.

Predicted Solar Flux for April 20-25 is 135, followed by 130 on
April 26-27, 105 on April 28, 100 on April 29-30, 95 on May 1-9,
then rising to 100 on May 10-12 and 105 on May 13-18 and 110 on May

Predicted planetary A index is 8, 5, 5, 7, 12, and 12 on April
20-25, 5 on April 26-29, 8 on April 30, 5 on May 1-7, and 8, 12, 15
and 10 on May 8-11, and 5 on May 12-20.

Alaska Dispatch ran an article with video on the solar flare
mentioned in K9LA's report below.  See it at

German ham Toni Umlandt, DD3EO mentioned another resource in
response to our mention in last week's bulletin ARLP015 of a public
remotely controlled SDR radio receiver in Walla Walla, Washington
that anyone can use via the internet.  He said to check  This lists 36 SDR receivers, and I think
all of them can be used simultaneously by multiple users.

K9LA's report:

Monday, April 16 gave us moderate solar activity, which was due to
an M1.7 X-ray flare from Region 1458 around 1745 UTC.  But since
then, solar activity has continued at low levels.  The daily 10.7 cm
solar flux is expected to slightly increase to around 120 during the
next several days.  There is an extremely small chance of X-Class
flares (1%) and a somewhat greater chance of M-Class flares (around

With solar activity continuing at low levels, the ascent of Cycle 24
noticeably slowed in the past couple months.  For example, after a
monthly mean 10.7 cm solar flux peak in November 2011 of 153, the
next three months saw ever-decreasing monthly means -- 141, 133, and
107 for December, January, and February, respectively.  March (last
month) recovered a bit with a monthly mean of 115, but April so far
appears to be headed for another low monthly mean (through April 18,
the 10.7 cm solar flux monthly mean is hovering around 102).  As a
side note, these up-and-downs in the monthly mean solar flux are
typical of a solar cycle.

But these recent low monthly means have taken their toll on the
smoothed 10.7 cm solar flux.  Since early 2009, the smoothed 10.7 cm
solar flux rose nicely.  The recent low monthly means have resulted
in the smoothed value pretty much leveling off in the past two
months at around 118.  This smoothed value is borderline for good
worldwide 10-Meter openings (especially East-West), so 10-Meters
will be at the mercy of the day-to-day variation of the F2 region.

Does this mean we've reached Cycle 24's peak?  Not necessarily --
other Cycles have had similar slow-downs, but then the solar
activity picked up again in terms of the monthly means to continue
the increase of the smoothed value.  The monthly means during the
next several months will be interesting to observe, and may give us
an early clue as to how high Cycle 24 will ultimately go.

Regardless of what happens with Cycle 24, the time is now to get on
the higher bands (especially 12-Meters and 10-Meters) to take
advantage of F2 region propagation.  If Cycle 24 performs to the
nominal prediction from the Marshall Space Flight Center
(, we're pretty much
there -- and we're not likely to have much mid latitude 50 MHz F2
propagation during this solar cycle (but watch for sporadic E links
to the equatorial ionosphere for Trans-Equatorial Propagation).  If
Cycle 24 performs more to the nominal prediction of the
International Space Environment Service
(, then we should have somewhat
better propagation on the higher bands in the next year or so.

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 April 12 through 18 were 50, 50, 65, 77, 86, 78,
and 96, with a mean of 71.7.  10.7 cm flux was 95.3, 97.7, 98.1,
101.7, 107.9, 113.8 and 121.5, with a mean of 105.1.  Estimated
planetary A indices were 13, 19, 9, 5, 5, 8, and 8, with a mean of
9.6.  Estimated mid-latitude A indices were 11, 13, 7, 5, 5, 8, and
7, with a mean of 8.


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