ARRL

ARRL Propagation Bulletin ARLP001 (2006)

SB PROP @ ARL $ARLP001
ARLP001 Propagation de K7RA

ZCZC AP01
QST de W1AW  
Propagation Forecast Bulletin 1  ARLP001
From Tad Cook, K7RA
Seattle, WA  January 6, 2006
To all radio amateurs 

SB PROP ARL ARLP001
ARLP001 Propagation de K7RA

Average daily sunspot numbers for the past week (December 29 through
January 4) were nearly 22 points below the previous period. Average
daily solar flux was about the same. Average daily mid-latitude
geomagnetic indices (A and K index) were exactly the same, and the
planetary A and K index were slightly lower.

For the near term expect sunspot numbers and solar flux to stay
around the same levels (low), but gradually rise to a short term
peak around January 15-16. The A and K index should also stay quiet,
with a returning active patch of Sun causing unsettled to active
geomagnetic conditions around January 16 and again around January
23-24. January 10-12 should have very quiet, stable geomagnetic
indicators.

Those forecasts are from the U.S. Air Force, via NOAA. Geophysical
Institute Prague expects quiet conditions for January 9-11, quiet to
unsettled today, January 6, and again on January 12, and unsettled
conditions January 7-8. Currently our Sun is quiet, and the
interplanetary magnetic field points north, both indicators of quiet
geomagnetic conditions.

Now that we have the solar flux and sunspot numbers for all of 2005,
it is time for a review of annual averages.

Average daily sunspot numbers for the years 1999 through 2005 were
136.3, 173, 170.3, 176.6, 109.2, 68.6 and 48.9. Average daily solar
flux for the same years was 153.7, 179.6, 181.6, 179.5, 129.2, 106.6
and 91.9. The steady decline over each calendar year since the
2000-2002 period should continue through the end of this year. Two
years from now we should know when trends turned around.

David Greer, N4KZ of Frankfort, Kentucky reports more surprising
short lived 10 meter propagation in the form of an opening toward
Europe on December 31. Last Saturday morning he heard many strong
European stations on 12 and 15 meters, so he went to 10 meters and
called CQ at 1427z with his 3-element Yagi pointed toward Europe.
I5KAP answered with a weak but readable signal. Dave reports, "Seven
minutes later I heard F5LIW calling CQ and worked him too.  Again,
signals were weak but readable. After we signed, he began calling CQ
again but with no takers from what I could hear. At 1439z, I heard
IK4GRO calling CQ. At S7, he had the strongest signal. We exchanged
reports and he began calling CQ again but no takers from what I
could hear. Then the signals were gone." Dave runs 100 watts on 10
meters.

Felipe Ceglia, PY1NB of the state of Rio de Janeiro in Brazil passes
word that he has a web site for DXers, which can be found at,
http://www.dxwatch.com/. He carries this bulletin, along with
spotting services.

Carl Luetzelschwab, K9LA sent in an interesting piece that he wrote
for this week's bulletin in response to an email exchange with Red
Haines, WO0W. It is titled "The T Index and SSNe."

Carl writes, "Due to the day-to-day variability of the ionosphere,
our propagation prediction programs use a monthly median model of
the ionosphere. Thus the prediction outputs (usually MUF and signal
strength) are statistical over a month's time frame. We have a
monthly median model, as opposed to a daily model, because the
developers did not find a satisfactory correlation between what the
Sun was doing on a given day and what the ionosphere was doing on
the same day. The proper correlation was between smoothed sunspot
number (or smoothed solar flux) and monthly median ionospheric
parameters (foE, foF2, hmF2, etc)."

He continues, "In order to get a better picture of what the
ionosphere is doing 'now', two similar methods have been developed:
the T Index and SSNe. The T Index comes out of Australia's IPS
(Ionospheric Prediction Service), and is named after its developer
Jack Turner. SSNe (equivalent sunspot number) was developed by the
US Air Force Global Weather Central organization, and is available
from Northwest Research Associates. The websites are,
http://www.ips.gov.au/HF_Systems/4/2 and,
http://www.nwra-az.com/spawx/ssne24.html, respectively."

Carl goes on to say, "Both of these methods basically vary the
sunspot number in a F2 region model of the ionosphere to force the
model to a best fit to current foF2 data from worldwide ionosondes.
Note the phrase 'best fit' - it's not a perfect fit, as the
ionosphere does not necessarily track at all locations. For example,
the F2 region ionization over the Millstone Hill (MA) ionosonde may
increase at a given hour, while just 400 miles away the F2 region
ionization over the Wallops Island (VA) ionosonde may decrease at
the same time."

He ends by saying, "What does using the T Index and SSNe buy us?
Neither gives us a daily model of the ionosphere due to the issue
cited in the previous paragraph. Nor does either take into account D
region and E region issues. But with respect to the F2 region, they
close the gap between the heavily averaged smoothed sunspot number
and short-term increases or decreases in sunspot activity (they also
can show the effect of geomagnetic storms). An example of this is
late December 2005. The official smoothed sunspot number for
December 2005 will come in somewhere between 10 and 20, but the
increased sunspot activity at the end of the year indicated that
using a sunspot number of 40 in your favorite prediction program
(from the SSNe website) would have given you a better 'now'
prediction."

Thank you, Carl!

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 and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at,
http://www.arrl.org/tis/info/propagation.html. An archive of past
propagation bulletins is found at, http://www.arrl.org/w1aw/prop/.

Sunspot numbers for December 29 through January 4 were 77, 67, 62,
41, 37, 39 and 25 with a mean of 49.7. 10.7 cm flux was 90.3, 89.9,
87.4, 87.4, 84.5, 84.9, and 84, with a mean of 86.9. Estimated
planetary A indices were 8, 7, 9, 4, 5, 3 and 2 with a mean of 5.4.
Estimated mid-latitude A indices were 7, 6, 9, 5, 5, 3 and 1, with a
mean of 5.1.
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/EX