ARRL Propagation Bulletin ARLP030 (2008)

ARLP030 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 30  ARLP030
From Tad Cook, K7RA
Seattle, WA  July 18, 2008
To all radio amateurs 

ARLP030 Propagation de K7RA

If today is like yesterday and the day before that, it will be the
twenty-sixth consecutive day with no sunspots.  Think this is bad?
At the last solar minimum there were only four days showing any
sunspots between September 5 and October 24, 2006.

Chuck Shinn, W7MAP of Coppell, Texas sent in an interesting
observation comparing the current solar minimum to the one between
cycles 18 and 19.  Cycle 19 was the biggest sunspot cycle on record,
and peaked around October 1957 to April 1958.

Chuck observed that there was a long period of little solar activity
in 1953 and 1954.  He used a table of smoothed sunspot numbers at and noted that from December 1953 through
most of 1954 the smoothed sunspot number was less than seven.

Each monthly smoothed number in this table represents an average of
monthly averages, I believe for 13 months, six months prior and six
months following.  That's why December 2007 is the last value shown
in this table, because to calculate the January 2008 number, you
need to know the average of daily sunspot numbers for all of the
current month, July 2008.

Looking at it this way, against the 1954 minimum, the current lack
of activity does not seem unusual, and the lack of 1954 sunspots
didn't indicate that cycle 19 would be below average.  The minimum
during that period was 2.4 in April, 1954.  Between cycles 19 and
20, the lowest value was 7.2 in June 1964.  From cycle 20 to 21,
March 1976 at 11.1 was lowest, and from cycle 21 to 22 it was
September 1986 at 10.  The last minimum was 8 in May and August

This puts the current minimum in an interesting perspective.  The
current minimum is quite low, but it hasn't yet lasted as long or
gone as low as the minimum preceding the largest sunspot cycle in
recorded history.

None of this, of course, can predict the size or length of the
upcoming cycle 24.

The August 2008 issue of Scientific American has an interesting
article concerning solar and geomagnetic activity titled ''Bracing
for a Solar Superstorm''.  It begins with a narrative describing a
huge space weather event on August 28, 1859, one hundred years prior
to twentieth century's cycle 19.  This was the fiercest ever
recorded, and resulted in shutdown of telegraph traffic and aurora
observed in the Caribbean.

The article says a storm of this magnitude comes along every 500
years or so, but reconstructs events and imagines the impact on
current technology infrastructure.  There are wonderful graphics and
numerous sidebars.  Included are some web links I wasn't previously
aware of, such as

Within that site at is a
history of great solar events, a short primer at, and at downloadable PDFs of the
book, ''The 23rd Cycle: Learning to live with a stormy star''.

Jeff Hartley, N8II of Shepherdstown, West Virginia sent a report on
more multi-hop sporadic-e activity, this time in the IARU contest
last weekend.  Jeff wrote, ''Condx would have been dreadful with a
high K index (peaked at 5) if not for the multi-hop sporadic E
during the IARU contest. I made about 20 QSO's on 10 running QRP and
was late getting there. There were Europeans/north Africans with
good signals on 10 from around 1530-19Z and again weaker from 2330
or earlier thru past 24Z.

''The HQ stations were like beacons (TM0HQ, 9A0HQ, S50HQ, GB7HQ,
OL4HQ, EH8U) operating whenever the bands were open. I couldn't get
thru to TM0HQ on 10M phone despite a loud S7-8 signal, but did get
them easily on CW. All together about 10 Eu Q's were made and a
couple with SA on 10M. 15M was open to all of EU except most of
Scandinavia at its best and RU1A had a good but unworkable signal
with my QRP. Best surprise was easily working ZD8Z on 20M who
usually enjoys huge pile-ups.

''2nd best was getting thru to OL4HQ on 75M SSB thru the QRN. 15 was
open well again in the last hour at 1100z.

''There was some action on 6M into EU from my area into CT and EA,
but I was too busy with the contest.''

Last week's bulletin should have reported on the upcoming weekend
geomagnetic activity.  For this week, geomagnetic conditions should
be mild in the beginning, increasing later.  Predicted planetary A
index for July 18-24 is 8, 5, 5, 5, 10, 15 and 12.  Geophysical
Institute Prague predicts quiet conditions for July 18, quiet to
unsettled July 19-20, quiet again on July 21, and unsettled July

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 at  For a detailed
explanation of the numbers used in this bulletin, see  An archive of past
propagation bulletins is at  Monthly
propagation charts between four USA regions and twelve overseas
locations are at  Instructions
for starting or ending email distribution of this bulletin are at

Sunspot numbers for July 10 through 16 were 0, 0, 0, 0, 0, 0, and 0
with a mean of 0.  10.7 cm flux was 65.4, 65.7, 64.9, 65.2, 65.6,
65.7, and 64.6 with a mean of 65.3.  Estimated planetary A indices
were 4, 7, 21, 14, 10, 7 and 7 with a mean of 10.  Estimated
mid-latitude A indices were 2, 6, 16, 10, 9, 7 and 4 with a mean of