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ARRL Propagation Bulletin ARLP044 (2005)

ARLP044 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 44  ARLP044
From Tad Cook, K7RA
Seattle, WA  October 21, 2005
To all radio amateurs 

ARLP044 Propagation de K7RA

Solar activity continues at low levels. Over the past reporting
week, every day but Wednesday, October 19 had a sunspot number of
11. Average daily sunspot numbers were down 8 points. Geomagnetic
conditions were also quiet.

Conditions for the near term look the same, with solar flux around
78 and geomagnetic conditions quiet to unsettled. Geophysical
Institute Prague predicts quiet conditions for October 21 and 23,
quiet to unsettled on October 25-27, and unsettled conditions on
October 22 and 24. A forecast from the U.S. Air Force shows the
planetary A index for today, October 21 at 5, and a planetary A
index around 12 for October 22-29.

Last week's propagation bulletin talked about the quarterly averages
of daily sunspot numbers, and trying to determine the bottom of the
solar cycle. Carl Luetzelschwab, K9LA mentioned that there haven't
been any sunspots from a new solar cycle yet (they switch magnetic
polarity) and referred to an interesting paper that talks about the
bottom of the last cycle. You can read it off the web at,

Carl highlighted the paragraph under Solar Activity, in which Karen
Harvey talks about the various factors that come into play when
trying to determine the minimum between the last and the next
sunspot cycle. Not only must the sunspot numbers be low, but for a
new cycle to be observed there must be a transition to a majority of
new-cycle spots compared to a minority of sunspots from the old
cycle. I believe the next Solar Cycle Prediction Panel meeting is in
spring 2006, so perhaps we'll know more then. Graham Rogers, VK6RO
wrote to say that he thinks of the bottom of the cycle when the
solar flux reaches 66.

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
bulletins is found at,

Sunspot numbers for October 13 through 19 were 11, 11, 11, 11, 11,
11 and 30 with a mean of 13.7. 10.7 cm flux was 78, 78.4, 79.6,
79.2, 78.1, 78.3, and 77.9, with a mean of 78.5. Estimated planetary
A indices were 4, 2, 2, 8, 13, 5 and 7 with a mean of 5.9.
Estimated mid-latitude A indices were 2, 1, 2, 5, 7, 5 and 3, with a
mean of 3.6.


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