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ARRL Propagation Bulletin ARLP031 (2005)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  July 22, 2005
To all radio amateurs 

ARLP031 Propagation de K7RA

Sunspots declined again to zero this week.  There haven't been any
spots on the Earth-facing disk of the sun for several days.  Average
daily sunspot number declined over 73 points to 18.1.  Average daily
solar flux was down nearly 26 points to 77.5.

Several readers inquired this week about negative sunspot numbers.
That's because a value of -1 appeared from NOAA as the sunspot
number for July 18 on numerous reports, including a daily summary of
several solar indicators, including solar flux, sunspot number and
sunspot area.  You can see it here at  But the -1 is just
a placeholder for a date when they have no data.  I haven't seen
this on their table of sunspot numbers before, but we see it every
day in their table of geomagnetic indices at  If you look at the
bottom of the table, you'll see a -1 for times that they don't yet
have data.  If you view this within the next three weeks, you'll
still be able to see July 15 and 16 and the -1 college A and K index
from Fairbanks, Alaska, where for some reason they were missing data
over a couple of days.

Expect sunspots to return.  Remember July 4, when the sunspot count
was so high, and that this area of the sun returns to view about
27-28 days later.  Look for a gradually rising solar flux and
sunspot number, peaking around August 1-5.  Predicted planetary A
index for this weekend, Friday through Monday, July 22-25 is 15, 10,
5 and 5.

If you would like to comment or have a tip, email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
bulletins is found at,

Sunspot numbers for July 14 through 20 were 61, 38, 16, 12, 0, 0 and
0 with a mean of 18.1. 10.7 cm flux was 89.9, 87.2, 76.3, 74.1, 72,
71.2 and 72.1, with a mean of 77.5. Estimated planetary A indices
were 11, 6, 9, 22, 34, 10 and 20 with a mean of 16.  Estimated
mid-latitude A indices were 7, 4, 10, 15, 19, 8 and 14, with a mean
of 11.


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