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ARRL Propagation Bulletin ARLP002 (2005)

ARLP002 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 2  ARLP002
From Tad Cook, K7RA
Seattle, WA  January 14, 2005
To all radio amateurs 

ARLP002 Propagation de K7RA

For the second reporting week for 2005 (January 6-12) both solar
flux and sunspot numbers were down, as expressed in the weekly
averages of the daily numbers. Average daily sunspot numbers
declined over 9 points to 31.6, and average daily solar flux was
down over 5 points to 89.9. These are not big point spreads, but at
this low level of solar activity there isn't much room for decline.
Eventually over the next two years we will see increasing periods of
consecutive days with a sunspot count of 0 and solar flux down below

The daily solar flux value is an expression of the noontime 2.8 GHz
energy detected at a sun-pointing receiving antenna in Penticton,
British Columbia. Canada's Dominion Radio Astrophysical Observatory
does the measurement, and you can see details along with a history
of this daily observation at, According to my
records, the lowest daily solar flux value measured over the past
decade was 64.9, on July 9, 1996. This was during a time when the
sunspot number was 0.

Solar activity has been rising over the past week. Right after this
bulletin was put to bed a week ago, the interplanetary magnetic
field near earth dropped sharply to the south, which made earth
vulnerable to geomagnetic storms. The geomagnetic indices (A and K
index) rose sharply from very quiet to very stormy on January 7 and
8. A few days later earth was inside a high-speed solar wind, and
conditions were stormy again on January 12. Fast growing sunspot 720
emerged, and this should increase the sunspot number and solar flux
over the next few days. See, for a
January 14 view of this fast growing spot.

Solar flux is predicted at 120 for January 14-15, and around 125 for
January 16-20. This is a sharp increase over the average daily value
of 89.9 for the past week and 95.4 for the previous week. Solar flux
values around 120-125 suggest daily sunspot numbers rising toward
(but not reaching) 100. Unsettled to active geomagnetic conditions
are predicted for January 14, and quiet conditions for the following

Last week's Propagation Forecast Bulletin ARLP001 didn't say
anything about disturbed conditions on the first days of 2005.
There was a powerful solar flare around 40 minutes into the UTC New
Year on January 1 (0040z, or 4:40 PM December 31 here on the West
Coast). The high latitude and planetary A and K indices rose
dramatically over the following two days. This produced disturbed HF
conditions. On January 2, the high latitude college A index (in
Alaska) rose to 64, and it was 44 and 41 over the next two days. The
planetary A index was up to 33 on January 2, indicating a
geomagnetic storm.

If you would like to comment or have a tip, email the author at,

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service propagation page at,

Sunspot numbers for January 6 through 12 were 14, 22, 34, 28, 40, 25
and 58 with a mean of 31.6. 10.7 cm flux was 83.2, 83.5, 88.5, 87.5,
90.1, 94.2 and 102.1, with a mean of 89.9. Estimated planetary A
indices were 4, 37, 30, 4, 6, 14 and 30 with a mean of 17.9.
Estimated mid-latitude A indices were 4, 21, 20, 3, 4, 9 and 18,
with a mean of 11.3.


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