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ARRL Propagation Bulletin ARLP047 (2003)

ARLP047 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 47  ARLP047
From Tad Cook, K7RA
Seattle, WA  November 21, 2003
To all radio amateurs 

ARLP047 Propagation de K7RA

The three sunspots that raised so much havoc at the end of October
are back after journeying across the sun's far side. Thursday,
November 20 had a planetary A index of 117, indicating a very strong
geomagnetic storm. The mid-latitude A index was 67, and Alaska's
College A index was 161. Average daily sunspot numbers for the week
rose to 63 from 32.6 last week. Average daily solar flux rose from
94.8 to 117.7, and the average daily planetary A index went from
23.4 to 31.7.

Over last weekend, a solar wind disturbed the earth's magnetic
field. Conditions were disturbed until November 19, when the
planetary and mid-latitude A indices were in a normal range. The day
before, Tuesday, November 18, sunspot 486 pushed a coronal mass
toward the earth. This was the event that caused all the upset two
days later on Thursday, November 20.

Ken Brown, N4SO, on the USNS Bowditch, a surveying ship in the
Military Sealift Command reports from somewhere around the South
China Sea that he copied the W1AW AMTOR FEC signal on 14.095 MHz at
2315z on November 18. Equipment was a Global Marine Distress and
Safety System receiver and a whip antenna. The path is over 8,000
miles. A projection with the W6ELprop software for that day shows
2300-0000z may be the end of a short opening probably beginning
around 2130z.

Rough conditions should subside over the weekend. Current projection
shows the planetary A index from Friday to Monday, November 21-24 at
45, 35, 20 and 20. Predicted solar flux values over the same period
are 180, 190, 200 and 210. High sunspot and solar flux levels are
expected to remain through Thanksgiving Day, November 27.

Diane Leveque, NH6HE, suggested a web site at Lockheed Martin Solar
and Astrophysics Laboratory that shows dramatic photos and
measurements of solar events. Check it out at

John Huffman, NA8M wrote "Conditions here in the northern latitudes
of Michigan are much different than for those folks in Florida and
Texas. Which propagation indicators should I look for to see if the
north, in particular, is going to have lousy conditions?"

John should check the mid-latitude K index transmitted by WWV at 18
minutes after each hour. It is updated every three hours, and when
it goes above 3, conditions will get rough, and the higher latitudes
feel it more than the lower. Every K index point represents a
significant change, and at the end of the day, the K indices are
used to calculate the A index for that date. A full day of K indices
at 3 would yield an A index at 15. A full day of K equal to 4 would
be A equal to 27, and with K equal to 5 the A would be 48. On
Thursday, November 20, the mid-latitude A index was 67. Starting
early in the UTC day (Wednesday evening in North America) the K
index was only 1, then it rose to 3, 5, 6, 5, 7, 7 and then 6.

Likewise, when the K index goes lower, the geomagnetic field is more
stable and HF paths should become more reliable. It can go all the
way down to zero.

In addition to receiving WWV for the K index, you can check the WWV
message on line at You
can also check recent A and K indices for mid-latitude, planetary
and high latitude values at Another option is to
call 303-497-3235. This isn't the number for the live WWV audio, but
a recording of the latest WWV message. Live WWV audio is at

Next week's Propagation Bulletin number ARLP048 will come early
because of the Thanksgiving holiday. Look for it on Wednesday,
November 26.

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

Sunspot numbers for November 13 through 19 were 25, 34, 52, 54, 72,
90 and 114 with a mean of 63. 10.7 cm flux was 102.1, 98.9, 97.8,
104.4, 121, 144.3 and 155.1, with a mean of 117.7. Estimated
planetary A indices were 42, 37, 40, 35, 34, 20 and 14, with a mean
of 31.7.


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