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ARRL Propagation Bulletin ARLP036 (2011)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 9, 2011
To all radio amateurs 

ARLP036 Propagation de K7RA

Solar indicators rose again this week, with average daily sunspot
numbers increasing nearly 21 points to 104.3, and average daily
solar flux up nearly 12 points to 115.5.  Geomagnetic numbers were
up as well, with the most active geomagnetic day occurring on
September 3.

We are just two weeks away from the Autumnal Equinox in the Northern
Hemisphere.  Look for increasing enhanced HF conditions as a result,
as we move from Summer conditions with its associated atmospheric
noise and daytime absorption.

The latest prediction from NOAA/USAF has solar flux at 105 for
September 9-10, 100 on September 11, 95 on September 12-13, 100 on
September 14-15, 105 and 103 on September 16-17, and 105 on
September 18-22.  Planetary A index is predicted at 5 on September
9, 18, 15, 10 and 8 on September 10-13, 5 on September 14-17, 7 on
September 18-19, and 5 on September 20-23.

Geophysical Institute Prague predicts minor storm for September
9-10, active conditions September 11, unsettled September 12, quiet
to unsettled September 13, and quiet on September 14-15.

Both the NOAA and Prague predictions for September 9-10 are probably
based on a series of recent solar flares beginning September 6 from
sunspot group 1283. These should deliver minor disruptions to Earth
on September 9-11, because the energy isn't squarely aimed toward
Earth. In another few days 1283 will be over our Sun's western limb
and outside the area of influence for Earth. An eruption from a
sunspot squarely in the center of the solar image has the potential
for the greatest impact here. 1283 was in the center of the solar
disc several days ago, but no longer.

See the web site
for an interesting article about sunspot group 1283. An eruption
from 1283 can be seen at
Note you can also select a high resolution image from that page.

Check for an interesting
video commentary on 1283.  Note that in the lower right you can
select a high definition image. Pay no attention to the comments
below the video regarding earthquakes, typhoons and planetary
alignment. Anyone can post these, and they are not based on any
sound science.

Max White, M0VNG of Worcester England sent in an article about the
Solar Dynamics Observatory and how they are using it to study solar
flares. Read it at,

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 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 September 1 through 7 were 119, 103, 139, 114,
102, 93, and 60, with a mean of 104.3. 10.7 cm flux was 111.8,
115.4, 118.7, 119.4, 118.7, 111.5, and 112.8, with a mean of 115.5.
Estimated planetary A indices were 3, 3, 13, 8, 6, 7, and 6, with a
mean of 6.6. Estimated mid-latitude A indices were 1, 1, 9, 7, 4, 5,
and 5, with a mean of 4.6.


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