ARRL Propagation Bulletin ARLP005 (2006)

ARLP005 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 5  ARLP005
From Tad Cook, K7RA
Seattle, WA  February 3, 2006
To all radio amateurs 

ARLP005 Propagation de K7RA

Solar activity is very low. Average daily sunspot numbers for the
week were down over 40 points to 9.1. Average daily solar flux
dropped nearly 11 points to 80.6. Geomagnetic conditions, with the
exception of January 26 were stable and quiet. On January 26 the
interplanetary magnetic field, which can shield the earth from solar
wind if it is pointing north, turned south, and the mid-latitudes
experienced some moderate geomagnetic activity, with the A index for
the day at 15. Polar regions saw a lot more activity, with the
College A index in Alaska going to 36.

Currently the sun is spotless since January 29. Daily readings of
zero sunspots could continue for another week. We will observe more
and longer periods such as this as we head toward the solar minimum,
still expected about to occur about a year from now. Geomagnetic
conditions should remain quiet, and solar flux around 77. This may
not begin to rise again until February 10.

January is over, so let us examine the average daily solar flux and
sunspot numbers for the month compared with previous months.

The average daily sunspot numbers for the months January 2005
through January 2006 were 52, 45.4, 41, 41.5, 65.4, 59.8, 68.7,
65.6, 39.2, 13, 32.2, 62.6 and 26.7. Average daily solar flux for
the same months was 102.3, 97.2, 89.9, 85.9, 99.5, 93.7, 96.5, 92.4,
91.9, 76.6, 86.3, 90.8 and 86.6.

As expected, the solar cycle is declining, but there is a lot of
variation from month to month.

Richard Buckner, who wrote the ACE-HF and ACE-HF Pro System
Simulation and Visualization Software for propagation prediction
mentioned in response to last week's bulletin that ACE-HF can do 160
meter predictions, but with some limitations. He sent along a quote
from the ACE-HF Basis for Predictions tutorial, written by George

"160-m Prediction Accuracy. 160-m frequencies are rounded to 2.0 MHz
to conform to VOACAP's lower frequency limit. VOACAP 2-MHz
predictions are reasonably accurate for NVIS and short-range
predictions out to about 1500 km. But when path distances are very
long, VOACAP becomes less accurate at night. At night, a residual
E-layer exists with a MUF usually above 2 MHz. It is this phenomenon
that permits AM broadcasts in the medium-wave bands to propagate
thousands of kilometers during nighttime hours. VOACAP, however, is
based on data that was collected at frequencies of 4 MHz and higher.
Extrapolation was used to cover the lower frequencies, but funding
limitations prevented the collection of further data to support
those extrapolations. Unfortunately, computed absorption values are
excessive in the extrapolations and the nighttime predictions thus
become excessively attenuated as path distance increases. For this
reason, 160-m nighttime predictions at long path distances should be
used with caution."

You can find more information on ACE-HF at,

We heard again from Charles Lewis, S9SS of Sao Tome (an island off
the West African coast, west of Gabon). On January 20 he wrote,

"I made 150 - 160M contacts last week. 51 were in North America,
coast to coast. It was, as usual, very slow, tedious going. E-mails
to me cited large pileups. As usual, I heard no pileup. Usually, I
hear only one, occasionally two, stations cresting my high level
noise. Even most "big gun" stations only get through when their
signal is enhanced greatly by whatever propagation phenomenon. Even
"little guns" find themselves all alone in the spotlight on my stage
now and then, despite all the better equipped callers. There is no
such thing as cracking the pileup on me on 160 meters since I never
hear it."

Charles continues, "In the Stew Perry, I heard only five NA stations
in close to three hours of listening and worked all five easily. It
was interesting that I heard one station on and off for nearly two
hours, while I heard the others only briefly for one period."

He goes on to say, "An interesting quirk here is a rogue LU 10 meter
beacon that I hear often on the IARU beacon frequency for hours at a
time when the band is so dead that I hear none of the IARU beacons.
Weird!! I favor the W3VD beacon when I am specifically looking for
an opening to the USA on 10M since, unlike 4U1UN, it transmits
continuously on 10 M."

He continues, "I used to experience the antipodes enhancement
phenomenon on the upper bands often when I was A22AA in 89-92. I
would often work Hawaiian hams (and hear WWVH) when the bands were
nearly in a blackout condition."

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 and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
propagation bulletins is found at,

Sunspot numbers for January 26 through February 1 were 24, 29, 11,
0, 0, 0 and 0 with a mean of 9.1. 10.7 cm flux was 86.9, 83.5, 80,
79.5, 78.8, 77.6, and 77.6, with a mean of 80.6. Estimated planetary
A indices were 29, 8, 6, 3, 1, 2 and 4 with a mean of 7.6. Estimated
mid-latitude A indices were 15, 7, 4, 1, 0, 1 and 3, with a mean of