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ARRL Propagation Bulletin ARLP023 (2004)

ARLP023 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 23  ARLP023
From Tad Cook, K7RA
Seattle, WA  June 4, 2004
To all radio amateurs 

ARLP023 Propagation de K7RA

The sun appears nearly blank.  Today one small spot, sunspot 621
faces earth, but there are no other noticeable areas of activity.
Only two days ago there were several more sunspots, but they are no
longer visible.  These sunspots didn't rotate off the visible disk,
but just faded from view.

Sunspot numbers and solar flux are understandably quite low.
Average daily sunspot numbers for the May 27 through June 2 period
was nearly 40 points lower than the daily average for the previous
seven days.  Over the same period, average daily solar flux was down
almost seven points.  Fortunately, geomagnetic activity was low.
Over the weekend conditions were unsettled, but otherwise several
days had mid-latitude geomagnetic A indices in the single digits.

Over the next week expect low geomagnetic activity.  Planetary A
index for June 4-8 is expected at 10, 8, 8, 10 and 10.  Solar flux
values for the same days are predicted to be 90, 95, 95, 100 and
100.  Solar flux is expected to peak between June 11-16 around 110.

Now that May is over, we should look at some monthly trends over the
last year.  The monthly average of daily sunspot numbers for May
2003 through May 2004 was 89.6, 118.4, 132.8, 114.3, 82.6, 118.9,
103, 75.7, 62.3, 75.6, 81, 59.3 and 77.  The monthly average of
daily solar flux for the same 13 months was 116.6, 129.4, 127.7,
122.1, 112.2, 155.5, 140.8, 116.1, 114.1, 107, 112.1, 101.2 and
99.8.  Solar flux hit a new monthly low during May for this downward
side of the solar cycle when it dropped below 100.

We're in a late spring propagation mode now.  The higher HF bands,
such as 10 and 12 meters, are seeing fewer openings, although this
month we should see sporadic E skip.  As the days grow longer,
absorption during daylight hours should increase.  Daytime
propagation on 20 meters won't be as good as a few months earlier,
but late night propagation should improve.  Also during the summer,
seasonal noise levels increase, probably more noticeable on 160, 80
and 40 meters.  40 meters should still be good for some long
distance nighttime propagation.

Field Day is still several weeks off, but currently the SEC 45 Day
AP forecast for planetary A index shows unsettled conditions
predicted for June 26 and 27 with A values of 15.  This is really
too early to tell, but the picture of conditions for that weekend
should become clearer as we approach the date.

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 May 27 through June 2 were 62, 52, 57, 64, 54,
76 and 63 with a mean of 61.1.  10.7 cm flux was 101.8, 102.4,
101.2, 99.6, 95.4, 90 and 90.4, with a mean of 97.3.  Estimated
planetary A indices were 6, 9, 14, 13, 14, 16 and 11, with a mean of
11.9.  Estimated mid-latitude A indices were 5, 6, 12, 11, 11, 14
and 9, with a mean of 9.7.


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