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ARRL Propagation Bulletin ARLP013 (2004)

ARLP013 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
From Tad Cook, K7RA
Seattle, WA  March 26, 2004
To all radio amateurs 

ARLP013 Propagation de K7RA

Solar flux and sunspot numbers rose this week, and geomagnetic K and
A indices were down. This is a perfect combination for the first
days of spring. HF operators always love to see the K index lower
than 3 and the A index below 10. There is nothing magic about those
numbers, but lower numbers are better, and those are below the
values (about K=3 and A=15) that we think of for unsettled

For quiet conditions, it's hard to beat this last Wednesday, March
24, when the mid-latitude K index was 0 for most of the reporting
periods. With sunspot numbers rising amid quiet geomagnetic
conditions, the springtime propagation over the past week has been

Average daily sunspot numbers rose nearly 27 points to 92.7 this
week (compared to last). The average daily planetary A index dropped
nearly 7 points to 8.7. Sunspot numbers and solar flux are rising,
and the predicted solar flux for this weekend, March 26-28 is 130,
135 and 130. This may be due to a pair of large sunspots emerging
over the sun's northeastern limb.

But early spring is also a time when auroras are more intense, which
of course is an indicator of elevated geomagnetic activity. This
weekend is the CQ World Wide WPX SSB Contest, and the outlook for
the next few days is good, with some active conditions probably
returning around March 29-30.

A bulletin received earlier today from the Australian Government IPS
Radio and Space Services warns that there may be rising geomagnetic
activity this Saturday, March 27 due to solar wind from a coronal
hole. One good daily resource for updates on solar wind streams is

Mark Dullea of Peabody, Massachusetts asked for a good source of
daily Ap readings (planetary A index). The place to go is the NOAA
Space Environment Center at  This is also a good
resource for comparing the daily variations in mid-latitude,
high-latitude and planetary geomagnetic indices mentioned in the
first paragraph.

Tony Salvate, N1TKS of Greenwich, Connecticut wrote for any thoughts
regarding a friend who is going fishing about 150 miles south of the
Arctic Circle in Northwest Canada this summer. He will be packing HF
gear along with a solar panel and batteries, and Tony wonders about
propagation to the Northeast United States. I noted that being so
far north, propagation will be strongly affected by geomagnetic
conditions, so hope for a K index lower than 3.

I also suggested calculating some paths with W6ELprop, the free
propagation prediction program from I
ran some projections for the end of June from Rae Lakes, Northwest
Territories (which is roughly the area Tony described) to Tony's
location and found some good possibilities for 40, 30 and 20 meters.

Users of Scott Craig's Solar Data Plotting Utility may or may not
have noticed a leap year error a few weeks ago. If you look at the
data file, February 29 is not there. Open the graph.dat file with a
text editor such as Windows Notepad, and insert 81 for sunspot
number and 110.0 for solar flux for the 29th.

If you haven't used Scott's program, you can download it from the
WA4TTK web site at This program
automatically sucks up the data from the end of each of these
bulletins and displays it in a nice graph running from January 1,

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the Propagation page on the
ARRL Web site at

Sunspot numbers for March 18 through 24 were 107, 89, 82, 65, 87,
110 and 109 with a mean of 92.7. 10.7 cm flux was 115.4, 112.2,
113.6, 111.2, 116.4, 118.3 and 119.7, with a mean of 115.3.
Estimated planetary A indices were 10, 6, 9, 13, 11, 8 and 4, with a
mean of 8.7.


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