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ARRL Propagation Bulletin ARLP031 (2004)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  July 30, 2004
To all radio amateurs 

ARLP031 Propagation de K7RA

Sunspot 652 has rotated out of view, but it was the source of major
excitement this week.  Coronal mass ejections caused big geomagnetic
storms on Sunday and Tuesday, July 25 and 27.  The planetary A index
was 122 on Sunday, 31 the next day, and 162 on Tuesday.  This caused
radio blackouts on the HF bands, but was a real blast for 6-meter
operators who reported great openings.  The activity was enhanced by
a south-pointing interplanetary magnetic field, leaving the earth
vulnerable to blasts of energy from the sun.

Aurora displays accompany periods of high geomagnetic activity, but
they tend to predominate at higher latitudes.  The stronger the
activity, the higher the K and A index, and the further south that
northern lights can be seen.  We're used to seeing photos of aurora
from Alaska, especially above the Arctic Circle, but at
you can view a photo taken July 27 at Borrego Springs in California.
This is only 20 miles north of the 33rd parallel, in Southern

Marc Weinberg, K9PET, sent a note about being maritime mobile in
Svalbard as JW/K9PET last week.  He was north of the 79th parallel,
and when geomagnetic disturbances hit, he said he ''thought the world
had disappeared''.  You can see a photo (taken from a distance) of
him operating on land from Raudfjorden Spitsbergen on July 20th.  Go
to and search for the photo accompanying the DER
(Daily Expedition Report) for the M S Endeavour for July 20th.  In a
few week's Marc will have more photos on his own web site,

Michael Tracy, KC1SX, sent in an interesting link for a Macromedia
Flash movie on HF propagation by AE4RV.  Watch it at

Over the next few days expect unsettled to active geomagnetic
conditions, and declining sunspot and solar flux numbers.  Predicted
planetary A index for Friday through Monday, July 30 through August
2 is 30, 20, 20 and 8.  Predicted solar flux for those same days is
95, 90, 85 and 90.  Solar flux is expected to peak again at about
125 around August 14-18.  More sunspot activity is ahead, at least
for the near term.

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 July 22 through 28 were 117, 86, 109, 130, 113,
66 and 66 with a mean of 98.1.  10.7 cm flux was 172.9, 165.1,
147.2, 156.2, 128, 118.1 and 100.7, with a mean of 141.2.  Estimated
planetary A indices were 19, 47, 27, 122, 31, 162 and 14, with a
mean of 60.3.  Estimated mid-latitude A indices were 13, 21, 29, 64,
26, 119 and 11, with a mean of 40.4.


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