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ARRL Propagation Bulletin ARLP010 (2008)

ARLP010 Propagation de K7RA

QST de W1AW =20
Propagation Forecast Bulletin 10  ARLP010
From Tad Cook, K7RA
Seattle, WA  March 7, 2008
To all radio amateurs=20

ARLP010 Propagation de K7RA

Following five days of no sunspots, we saw one (number 984) on March
5 and 6, but it is fading off the west limb of the earth-facing
portion of the Sun.  Solar activity is still very low.

Last week we reported, in error, that an opening on 6 meters
extended to VP6DX.  The openings were actually on 10 meters.

Last week saw a geomagnetic disturbance on February 28 through March
1, caused by solar wind streams from a coronal hole.  The far north
saw dramatic aurora displays, and the Planetary A index on those
last days were 22, 27 and 19.  But the far-north College A index,
measured near Fairbanks, Alaska on the same dates was 27, 44 and 44.

It seems the geomagnetic activity, which is stronger in the far
north because of a concentration of magnetic lines of force at the
poles, had a bit of a hangover compared to the Planetary A index and
the mid-latitude A index (17, 18 and 13).  The A index at 44 is
dramatically high, and the storm hung over for an extra day compared
to the lower latitudes.

At the start of every month we've been calculating a new average
based on the previous three months of sunspots.  This seems like it
may be a way to spot solar minimum in less time than looking at
12-month smoothed numbers.

May 06 39.7
Jun 06 28.9
Jul 06 23.3
Aug 06 23.5
Sep 06 21.2
Oct 06 24.1
Nov 06 23.1
Dec 06 27.3
Jan 07 22.7
Feb 07 18.5
Mar 07 11.2
Apr 07 12.2
May 07 15.8
Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07  5.4
Oct 07  3
Nov 07  6.9
Dec 07  8.1
Jan 08  8.4

January 2008 is the new figure, because it is a three-month average,
and January is the middle-month, now that we can average all the
sunspot numbers for December, January and February.

The numbers still seem to suggest a possible sunspot minimum last

For the next week, NOAA and the US Air Force predict a planetary A
index of 5, 15, 15, 10, 10, 15 and 10 for March 7-13.  Geophysical
Institute Prague predicts unsettled to active conditions March 7,
active geomagnetic conditions March 8, and unsettled conditions
March 9-13.

Peter Morrison, EI9ES advises that he likes IonoProbe, a shareware
program from Afreet Software that sits in your computer system tray
and monitors sunspot numbers, solar flux, and geomagnetic indices.
The tool was written by VE3NEA, and you can download it from

Also at that site are other interesting and useful programs,
including Morse Runner, a CW contest simulator that reminds me of
the old Doctor DX program produced years ago for the C-64.  Using it
seems almost like being on the air.

Spring Equinox, always a good time for HF propagation, is less than two
weeks away.  Let's hope for sunspots to go with it.

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

Sunspot numbers for February 28 through March 5 were 12, 0, 0, 0, 0,
0, and 13 with a mean of 3.6.  10.7 cm flux was 70, 69.8, 68.6,
69.2, 68.4, 68.3, and 69.3 with a mean of 69.1.  Estimated planetary
A indices were 22, 27, 19, 8, 5, 4 and 8 with a mean of 13.3.
Estimated mid-latitude A indices were 17, 18, 13, 8, 4, 3 and 7,
with a mean of 10.


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