ARRL

ARRL Propagation Bulletin ARLP006 (2013)

SB PROP @ ARL $ARLP006
ARLP006 Propagation de K7RA

ZCZC AP06
QST de W1AW  
Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7RA
Seattle, WA  February 8, 2013
To all radio amateurs 

SB PROP ARL ARLP006
ARLP006 Propagation de K7RA

Average daily sunspot numbers hardly changed from last week and the
week prior, but average daily solar flux bounced back to about the
level it was from two weeks ago.

Average daily sunspot numbers were down five points to 50.7, and
average daily solar flux was up 7.7 points to 106.4.

Predicted solar flux values are 105 on February 8-10, 110 and 105 on
February 11-12, 100 on February 13-14, 110, 115 and 110 on February
15-17, 115 on February 18-19, 110 on February 20-21, 105 on February
22, 115 on February 23-24, then 110, 105 and 100 on February 25-27,
95 on February 28 through March 2, 115 on March 3-4, 120 on March
5-6, and 125 on March 7-8.

The predicted planetary A index is 22, 15 and 10 on February 8-10, 5
on February 11-18, 8 on February 19, 5 on February 20-21, then 15,
10 and 8 on February 22-24, 5 on February 25-28, 10 and 8 on March
1-2, 5 on March 3-7, and 8 on March 8-9.

OK1HH says geomagnetic activity should be quiet to unsettled on
February 8, quiet to active February 9-10, quiet to unsettled
February 11-12, quiet to active February 13-14, quiet to February
15-16, quiet February 17-21, active to disturbed February 22-23,
quiet to unsettled February 24-25, quiet on February 26-27, mostly
quiet February 28, quiet to active March 1, quiet to unsettled March
2, and mostly quiet on March 3.

I've been looking at the predictions for planetary A index and solar
flux, and it is interesting to note how they change over time.  The
planetary A index prediction for February 3 for over a month was a
value of 5, until January 31, when it changed to 18. Then on
February 1 it was 15, and the same on February 2.  But on February
3, the actual value was 4.  A similar thing happened with the
February 4 prediction. It was 5 up until January 31, when it changed
to 15, then for March 1 and 2 it was 12, then it changed back to 15
on March 3.  The following day, March 4, the actual value was 4
again, just as it was the day earlier.

On February 7 the planetary A index prediction for February 8 is 22,
and on February 6 the prediction for February 8 was 8.  Prior to
that it was 5. We will see the actual value at the end of the day
today, February 8.

We heard from Fabrizio Valdirosa, a shortwave listener in Italy, who
inquired about the average sunspot number for all of 2011. We
mentioned recently that it was 29.9, but Fabrizio thought this was
too low while looking at the monthly averages at,
http://www.swpc.noaa.gov/ftpdir/weekly/RecentIndices.txt.

I recalculated by again totaling all of the daily sunspot numbers
for 2011, which is 29,239. Divide that by 365 days, and we get an
average daily sunspot number for that year of 80.1. I have no idea
how 29.9 was previously calculated, except that I somehow came up
with a total for the year of 10,913 instead of 29,239 and it was my
own error. So the average yearly sunspot numbers for 2008-2012 were
4.7, 5.1, 25.5, 80.1 and 82.3.

Don Street, HS0ZEE wrote to ask about seasonal variations mentioned
in the bulletin, and asked, "Here in Asia, Spring and Fall are not
so well defined, perhaps for reader like me it would be helpful to
mention which month you refer to." We are just referring to the
seasons as the time between Equinox and Solstice, Solstice to
Equinox, etc.  This page gives the dates for the seasonal changes:

http://wwp.greenwichmeantime.com/longest-day/equinox-solstice-2010-2019.htm.

Don also likes the HAP charts for HF propagation produced by the
Australian government and notes, "I find the charts near to actual
band conditions. Unfortunately they are based on the previous hours
observed conditions, but still very useful."

Here is the link Don refers to:

http://www.ips.gov.au/HF_Systems/6/6/1.

Bill Bliss, W1WBB of Portsmouth, Rhode Island wrote: "Don't believe
I've seen these two new forecast products from the SWPC mentioned in
your weekly column, found via link on their home page:
http://www.swpc.noaa.gov/index.html

"They are issued twice daily and I've found them helpful as an
additional tool for predicting near-term propagation on the HF/MF
amateur bands.  Links for feedback on both the 3-Day Forecast and
the Forecast Discussion are also provided.  Positive feedback on
these 'experimental' products from the amateur community (accepted
up through Feb. 12) may help ensure they become a permanent part of
SWPC's Data and Products area."

If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at
http://arrl.org/propagation-of-rf-signals. For an explanation of the
numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past
propagation bulletins is at
http://arrl.org/w1aw-bulletins-archive-propagation. Find more good
information and tutorials on propagation at
http://myplace.frontier.com/~k9la/.

Monthly propagation charts between four USA regions and twelve
overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL
bulletins are at http://arrl.org/bulletins.

Sunspot numbers for January 31 through February 6 were 47, 65, 54,
79, 30, 41, and 39, with a mean of 50.7. 10.7 cm flux was 102.7,
103.7, 111.8, 111.1, 106.7, 105.1, and 103.5, with a mean of 106.4.
Estimated planetary A indices were 1, 4, 9, 4, 4, 2, and 2, with a
mean of 3.7. Estimated mid-latitude A indices were 1, 4, 9, 6, 3, 2,
and 2, with a mean of 3.9.
NNNN
/EX