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ARRL Propagation Bulletin ARLP020 (2011)

ARLP020 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 20, 2011
To all radio amateurs 

ARLP020 Propagation de K7RA

A decline in sunspot activity this week showed as a 23 point drop in
average daily sunspot numbers, and nearly 9 point decline in average
daily solar flux.  These compare, of course, to the numbers for the
previous reporting week, which always runs from Thursday through

But with this decline in activity there were three new sunspot
groups on May 14, and then one new sunspot group each day following,
through May 18.  But on May 19, there was no new sunspot group, and
the daily sunspot number declined from 65 on Wednesday to 36 on
Thursday.  Heightened geomagnetic activity occurred from May 15-17,
with the planetary A index in the low double-digits.

The latest prediction from NOAA/USAF is for much lower solar flux
than predicted on Wednesday, May 18.  The forecast predicts solar
flux readings of 84 and 82 on May 20-21, then 80 on May 22-26,
jumping to 90 on May 27 and 110 on May 28-30.  Predicted planetary A
index is 7 on May 20-21, 5 on May 22-25, then 8, 22, 18, 15, 15 and
8 on May 26-31.

Geophysical Institute Prague predicts quiet conditions May 20-21,
quiet to unsettled May 22, and quiet May 23-26.

On Wednesday, May 18 the solar flux was predicted at 92 on May
20-26, much higher than numbers forecast a day later and referenced

Last week's Propagation Forecast Bulletin ARLP019 mentioned that
most sunspots lately appear in the Sun's northern hemisphere, but on
May 19 they are all in the southern hemisphere.  Go to and on the upper right check the archive
for May 18.  Note the two sunspot groups, 1214 and 1216, in the
southern hemisphere.  Now change to May 19, and note sunspot group
1218, also in the southern hemisphere.  On May 20 it shows all
sunspots only in the southern half.

Today the new June 2011 issue of WorldRadio Magazine is available
online, for free.  Go to to
download the latest issue, and check out Carl Luetzelschwab, K9LA's
propagation column on pages 30-33.  He gives an interesting treatise
on solar flux and sunspot numbers.

The only mail this week was from K4FNC, and is not the usual type of
question about propagation, but he asked, "Can you tell me when is
the best time to make contact with the space station on 2 meters or
the 440 frequencies?"  Quite a bit of information on ARISS is on the
ARRL web site at

If you click on the "Frequently Asked Questions" link on the left
side, this gives you a lot of the details, such as how to track the
space station.  The link to AMSAT at even gives a method for
tracking that doesn't need your own tracking software.  Click on
Online Satellite Pass Predictions, select ISS, and enter FM05nb for
the grid square for K4FNC, click Predict, and this gives the time
for AOS (Acquisition of Signal) and LOS (Loss of Signal) for his

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 May 12 through 18 were 29, 29, 64, 54, 63, 57,
and 65, with a mean of 51.6. 10.7 cm flux was 92.8, 91.5, 91.4,
94.5, 92.2, 91.5, and 90.6, with a mean of 92.1. Estimated planetary
A indices were 3, 4, 4, 11, 12, 10, and 6, with a mean of 7.1.
Estimated mid-latitude A indices were 2, 3, 3, 9, 10, 8, and 4, with
a mean of 5.6.


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