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ARRL Propagation Bulletin ARLP037 (2014)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 12, 2014
To all radio amateurs 

ARLP037 Propagation de K7RA

We saw a nice increase in the level of solar activity this week, and
the outlook for the near term looks good, or at least, interesting.

Average daily sunspot numbers for the period September 4-10
increased from 85.1 to 152.1, and average daily solar flux rose from
126.7 to 155.8. Geomagnetic indicators were quiet, with average
planetary A index declining from 14.7 to 7.9, and average
mid-latitude A index dropped from 13.4 to 8.3. These latest numbers
are compared to the previous seven days, August 28 through September

Http:// reports a couple of CME blasts are headed
toward Earth, and they were launched September 9 and 10 from sunspot
2158.  The sunspot was in a most favorable position for launching
ejections in our direction. It was right in the center of the
visible solar disc from Earth's perspective. Don't worry, this is
not some doomsday event, although it is strong.

At 0520 UTC on September 11 (which was 10:20 PM September 10 on the
West Coast) the Australian Space Forecast Centre issued a
geomagnetic warning. They predict increased geomagnetic activity on
September 11-13 due to coronal mass ejections. Their forecast calls
for unsettled conditions with possible minor storm periods on
September 11, active to major storm levels September 12, and active
geomagnetic conditions September 13.

From NOAA/USAF the predicted planetary A index is 40, 60, 25 and 12
on September 12-15, 5 on September 16-24, then 18 on September 25,
15 on September 26-27, 12 on September 28-29, 10 on September 30 and
5 on October 1-4.

Predicted solar flux is 152 on September 12, 150 on September 13-14,
148 on September 15-16, 146 on September 17, 145 on September 18-20,
then 150, 145 and 135 on September 21-23, 130 on September 24-25,
125 on September 26-27, 130 on September 28-29, 145 on September
29-30, then 150, 145 and 140 on October 1-3, 135, 140 and 145 on
October 4-6 and 150 on October 7-11.

Expect aurora in northern latitudes (in the Northern Hemisphere) and
rough HF conditions on Friday, September 12. The predicted planetary
A index of 40 on Friday and 60 on Saturday indicates a moderate to
strong geomagnetic storm.

You can watch the fun at which is updated
every three hours. When you see the K index above 3, this indicates
active geomagnetic conditions. Each single point higher represents a
large increase in activity.

The A index represents an average of each 3-hour K index over 24
hours. It is not meaningful to average the K index directly because
it is non-linear, so the number is converted back into a value which
has a direct linear relationship to the magnetometer readings upon
which the K index is based, then it is averaged.

So if over the course of a day all eight K index values were 4, the
A index is 27. If all readings were 5, then the A index is 48 and a
K index of 6 is equivalent to an A index of 80. You can see the
scale at the bottom of the page on .
This also shows an example of the averaging used to produce a daily
A index.

Because the A index predicted for Saturday is 60, we know that the K
index should be between 5 and 6 all day. Looking at the chart of the
Space Weather Scale for Geomagnetic Storms at shows this correlating to a
Minor to Moderate geomagnetic storm. Of course the K index could
briefly go much higher, perhaps to 7 and still result in an A index
somewhere around 60, so during that brief period when the planetary
K index is 7 the storm level would be Strong.

Let's look at the prediction of geomagnetic activity from OK1MGW in
the Czech Republic. He predicts the geomagnetic field will be active
to disturbed September 12-15, quiet to unsettled October 16-17,
mostly quiet September 18-19, quiet September 20-21, quiet to active
September 22, active to disturbed September 23-24, quiet to
unsettled September 25-26, quiet to active September 27-28, quiet to
unsettled September 29 to October 1, quiet to active October 2-3,
and mostly quiet October 4-8. He expects an enhanced solar wind on
September 12-15, 22-23 and 26-29.

On September 10 Jon Jones, N0JK wrote, "An impressive sporadic-E
opening appeared September 7, which later formed Es links to TEP on
to South America September 8, UTC.

"There was an early morning (1230z) double hop Es opening from
Puerto Rico to the southern states as far west as New Mexico on the
September 7. Later in the afternoon single hop Es ran from the
Midwest to the southeast states, then a strong double hop Es opening
from Puerto Rico to the Midwest states. NP4A was over S-9 for over
an hour to Kansas, Missouri and Nebraska around 2215z. Later Es -
TEP from IA, MN, IL, and W4 to CE, CX, LU and PY.

"It will be interesting to see what develops from the two CMEs en
route to Earth."

Over the next few days expect diminished HF propagation due to high
geomagnetic activity, but this may produce interesting propagation
on 6 meters. After a few days the effects should wear off. Now we
are just 11 days away from the Autumnal Equinox, which is a time of
improving HF propagation. The equinox occurs at 0229 UTC on Tuesday,
September 23.

With the recent flare activity, the popular press has taken note.
This article appeared locally here in Seattle, and mentions the
possibility of aurora:

The professor quoted in the article is WB7NWP. Note his suggestion
to check this online tool, which I am not sure I've seen before: .

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 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 September 4 through 10 were 136, 124, 170, 154,
158, 162, and 161, with a mean of 152.1. 10.7 cm flux was 146,
143.9, 157.3, 160.2, 163.9, 159, and 160, with a mean of 155.8.
Estimated planetary A indices were 7, 8, 9, 8, 6, 8, and 9, with a
mean of 7.9. Estimated mid-latitude A indices were 7, 10, 7, 10, 7,
8, and 9, with a mean of 8.3.


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