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ARRL Propagation Bulletin ARLP043 (2008)

ARLP043 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 43  ARLP043
From Tad Cook, K7RA
Seattle, WA  October 17, 2008
To all radio amateurs 

ARLP043 Propagation de K7RA

Finally, we are seeing Cycle 24 sunspots that don't emerge one day,
and evaporate the next.  That's right -- sunspots, as in two or
more.  On Friday, October 10 sunspot 1005 emerged at high latitude
over our Sun's eastern limb, and that day's sunspot number was 12.
On the following day the sunspot number rose to 16, and a solar wind
emerging from a coronal hole caused a geomagnetic storm.  Planetary
A index rose from a quiet 3 on Friday to 37, and the mid-latitude A
index was 20.  The 3-hour planetary K index reached a maximum of 7
that day, a high value for that scale.  Since then conditions have
quieted again.

On Sunday, Monday and Tuesday -- as the spot progressed toward the
center-north of the solar disk -- sunspot numbers were 16, 15 and 14
as the dark spot began to fade.  On Wednesday the sunspot number
faded another point to 13, but on Thursday, October 16, sunspot 1006
emerged, but this time in the southwest corner, about to rotate out
of view.  The sunspot number for Thursday jumped to 24.

On Wednesday of this week a reading of activity on the side of the
Sun facing away from Earth found another possible sunspot.  This was
detected using a method called helioseismic holography, which
depends on pressure waves bouncing around our Sun's interior.  For
more detail, take a look at,  Also the

Mike Donnelly, KG9M of Woodstock, Illinois wrote to ask, "What does
'unsettled conditions' really mean? Good for DX or not???  Same
question for 'quiet,' too."

Unsettled, active, and quiet refer to geomagnetic indices, the K
index and the A index.  We generally want those numbers to be low,
or quiet, as absorption is lower and polar propagation paths work
better.  An exception would be VHF aurora propagation, when the
numbers are high.

The effects of geomagnetic activity are much greater when operating
from the far north.  Sam Vigil, WA6NGH of San Luis Obispo,
California says that during the summer of 2005 he and his wife Eve,
KF6NEV paddled 720 miles down the Teslin and Yukon rivers from near
Whitehorse in Yukon Territory to Circle, Alaska.  They brought a 40
meter QRP transceiver and a general coverage shortwave receiver on
the trip, which ran from July 25 to August 28.

Sam notes there were long stretches when he heard nothing at all on
either radio.  The latitude ranged from 60.7 degrees north to 65.8
degrees north.

He is searching for archives of A and K index data for northern
latitudes, and noticed that our bulletin -- which is archived at the
ARRL web site -- only gives a mid-latitude and a planetary number.
He is giving a talk about his trip at Pacificon
( this weekend and is looking for
historical data.

I found it on,
and noted that periods of high geomagnetic activity corresponded to
periods when he heard no signals.  The index to watch for far
northern latitudes is the college A and K index, which is from a
magnetometer at University of Alaska, which is at 68.68 degrees
north.  The observatory has a web page at,

Peter Thulesen, OX3XR of Nuuk, Greenland (64 deg N, 51 deg W) wanted
geomagnetic data that is appropriate for his high latitude, and I
suggested recent data updated daily from,  This is the same
source we use for the indexes at the end of our bulletin, but we
don't list the Alaska college index here.

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 web page 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 October 9 through 15 were 0, 12, 16, 16, 15, 14,
and 13 with a mean of 12.3.  10.7 cm flux was 68.7, 68.9, 70.8,
70.1, 70.9, 70.4, and 70.9 with a mean of 70.1.  Estimated planetary
A indices were 2, 3, 37, 13, 9, 4 and 8 with a mean of 10.9.
Estimated mid-latitude A indices were 1, 2, 20, 10, 7, 3 and 7 with
a mean of 7.1.


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