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ARRL Propagation Bulletin ARLP019 (2006)

ARLP019 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 19  ARLP019
From Tad Cook, K7RA
Seattle, WA  May 12, 2006
To all radio amateurs 

ARLP019 Propagation de K7RA

This week saw higher geomagnetic activity and lower sunspot numbers
than the previous period (our reporting week is Thursday through
Wednesday). Average daily sunspot numbers declined over five points
to 54.3. For today, May 12, look for active geomagnetic conditions,
with a planetary A index predicted at 25, then declining to 12 and
10 on Saturday and Sunday. Sunspot numbers and solar flux should be
a bit lower than the past week.

Geophysical Institute Prague predicts active geomagnetic conditions
for today, May 12, unsettled May 13, quiet to unsettled May 14, nice
and quiet on May 15-16, back to quiet to unsettled for May 17, and
unsettled conditions on May 18.

A rash of email arrived this week alerting us to a new long-range
sunspot cycle prediction. Only this time it isn't for upcoming cycle
24, but the peak of cycle 25, reaching solarmax around 2022.

Think that's a long way off? It depends on your perspective, which I
suspect is determined by the proportion a given time period
represents when compared to the time you've been alive. For
instance, when starting out in early 1965 as WN7CSK, and still 12
years old, looking ahead 16 years I would be 28, and the year 1981,
hard to fathom at the time. The old-timers I knew then, such as
Howard S. Pyle, W7OE, first on the air around the same age in 1907,
would have laughed out loud at such an assessment.

This spring it was 16 years since I began writing this bulletin.
And 16 years from now, in mid 2022, I will turn 70, a terrifying
notion, because the last 16 years went by so fast. I suspect the
next 16 years to flash by quickly. Even if beginning our ham life at
a young age, we don't get to see many solar cycles. Let's hope the
soon-to-begin cycle 24 is huge, reminiscent of the awesome cycle 19
of the 1950s.

We saw a prediction in March that the upcoming cycle 24 could be a
big one, from a recent prediction by Mausumi Dikpati. (See the 2006
Propagation Forecast Bulletin ARLP010 at,, and the NASA
article at,

Using the same method of indirectly observing a massive circulating
current of solar plasma, a report from NASA solar physicist David
Hathaway shows a stunted-looking cycle 25. Read about it in an
article from Dr. Tony Phillips at,

Roger Barnhill, AB8RX of Lansing, Michigan asks, "Where can I find
up-to-date info on which way the Earth's magnetic field is pointing
at any particular time?"

You can find this at Look down the
left side under Interplanetary Magnetic Field. When it is pointing
south, Earth is vulnerable to solar wind, and more likely to
experience greater geomagnetic activity.

HS0ZFQ sent in a link to a page titled, "The short history of the
Smoothed Sunspot Number" at, This
discusses the various sources for smoothed sunspot numbers needed
for propagation prediction programs using the VOACAP (Voice of
America Coverage Analysis Program) engine. One example called HamCAP
is from VE3NEA. It is free, and you can get it at,

Mike Schaffer, KA3JAW is in Florida, where he enjoys observing
sporadic-E propagation on broadcast television. On May 11 at 1750z
and again at 2215-2230z he observed Canal 2 on television channel 2,
about 1100 miles from him in Nicaragua.

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 at,

Sunspot numbers for May 4 through 10 were 50, 61, 69, 64, 53, 56 and
27 with a mean of 54.3. 10.7 cm flux was 91.8, 86.7, 87, 86.2, 84.7,
82.6, and 78.2, with a mean of 85.3. Estimated planetary A indices
were 14, 13, 24, 19, 8, 4 and 4 with a mean of 12.3. Estimated
mid-latitude A indices were 10, 8, 14, 17, 5, 2 and 4, with a mean
of 8.6.


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