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ARRL Propagation Bulletin ARLP021 (2007)

ARLP021 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 21  ARLP021
From Tad Cook, K7RA
Seattle, WA  May 18, 2007
To all radio amateurs 

ARLP021 Propagation de K7RA

This week saw a rise in sunspot numbers, with the average daily
value up over 11 points to 29.3.  On Wednesday, May 16, the daily
sunspot number was 56, the highest daily reading since 162 days
earlier on December 5, 2006, when the sunspot number was 59.  This
week's average sunspot number was the highest since the reporting
week of January 4-10, 2007.

Keep in mind that a tremendous day-to-day variation in sunspot
numbers is normal, so this should not be seen as an indicator that
sunspot trends have turned around, and are already into Cycle 24.
Of course, increased activity may follow; this just isn't an
indicator that higher sunspot numbers are due in the very near term.

The bottom of the cycle, late last year predicted for the past
couple of months, has moved out as far as a year in the most recent
general consensus of the scientific community.  With predictions
revised so often, it would be useful to keep an eye on each week's
release of the Preliminary Report of Solar and Geophysical Data at,

Lately about once per month the report shows a revised projection of
smoothed sunspot numbers through the next calendar year around pages
10-12.  The last one was in the May 1 issue, #1652.  This shows the
minimum smoothed numbers from January to June of this year.  Compare
this to the projection in issue #1627 from November 7, 2006, which
had the minimum more tightly predicted to March and April of this

This week brought reports of seasonal sporadic E layer openings on
10 and 6 meters.

Rich Klinman, W3RJ of Coopersburg, Pennsylvania wrote on May 11
noting that both 10 and 6 were good for him. He says, "I could
easily work from WI to FL and WA to CA including HI to the West.
Central and South America late in the afternoon into night. Day
after day.  Morning until after midnight."

Bill Tackett, KN4N of Greenville, Tennessee wrote, "10 meters was W
I D E open here Friday May 11 from East Tennessee to the North. We
were working stations all the way to Canada mobile with good strong
signals. It opened around 0900 DST time and stayed opened until
around 1330 DST."

Greenville is in the Eastern Time zone, so daylight standard time
there would be 1300-1730z.

Two weeks ago (May 4) Byron Stoesser, W7SWC was riding his bike in
Southern Arizona and working the low end of 17 meters.  He was
surprised to observe short and long skip contacts back-to-back,
first with N6KN in Los Angeles, then CT1IZU in Portugal.  No word on
the time of day, but the afternoon looks good for the path to Europe
on that day.

For the near term, we will probably see sunspot numbers higher than
the recent periods when it was 0 or 12, but declining a bit, with
the next probable peak around May 25-30.  Unsettled to active
geomagnetic conditions are forecast for the beginning of that
period, and we may see some mildly unsettled activity around May 20.
We are still in the right season for sporadic E propagation on 10
and 6 meters.

Geophysical Institute Prague predicts quiet conditions for May 18,
unsettled May 19 and 20, quiet May 21-23, and unsettled to active on
May 24.

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 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 May 10 through 16 were 20, 24, 21, 18, 29, 37
and 56 with a mean of 29.3. 10.7 cm flux was 71.2, 71.5, 71.4, 73.5,
72.9, 76.9, and 77.1, with a mean of 73.5. Estimated planetary A
indices were 3, 2, 3, 3, 3, 6 and 4 with a mean of 3.4. Estimated
mid-latitude A indices were 2, 2, 2, 2, 1, 4 and 3, with a mean of


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