ARRL

ARRL Propagation Bulletin ARLP001 (2003)

SB PROP @ ARL $ARLP001
ARLP001 Propagation de K7VVV

ZCZC AP01
QST de W1AW  
Propagation Forecast Bulletin 1  ARLP001
From Tad Cook, K7VVV
Seattle, WA  January 3, 2003
To all radio amateurs 

SB PROP ARL ARLP001
ARLP001 Propagation de K7VVV

Last week this bulletin reported sunspot numbers dropping
dramatically, and this week it became a trend. Average daily sunspot
numbers for the past three weeks were 206.1, 164.4 and then 55.3 for
this week. Average solar flux was 188.7, 169.1 and 117.1.  The real
shocker was Monday, with a sunspot number of only 44. I thought
perhaps the sunspot number wasn't this low since the other side of
the solar cycle (before the peak), but we actually saw lower values
of 27 and 38 on September 11 and 12, 2000. But the previous value
that was this low probably was on the other side of the peak, on
September 26, 1999 when it was also 44.

Last year was surprisingly good if you like high sunspot activity.
The average daily sunspot number for the 2002 calendar year was
actually slightly higher than any of the three previous years.
Average daily sunspot numbers for the years 1997 through 2002 were
30.7, 88.7, 136.3, 173, 170.3 and 176.6. Note the 176.6 value is
lower than the 178.3 reported in last week's bulletin as the average
sunspot number for the first 359 days of the year. The drop in
sunspot numbers over the past week was so dramatic that it actually
dropped the yearly average by nearly two points. Average daily solar
flux for the same six years was 81, 117.9, 153.7, 179.6, 181.6 and
179.5.

What is the trend though? Next we'll look at quarterly averages.

Average daily sunspot numbers for the past eight quarters was 147.3,
164.8, 170.4, 198.1, 178.3, 165.3, 193.5 and 152.7. Average daily
solar flux for those same quarters was 164.4, 166.7, 175.5, 219.1,
203.9, 156.4, 178.1 and 164.2. As you can see, there is quite a bit
of variability in the values. Solar cycles only look smooth when
looking backward and doing a moving average of the data.

Currently earth is entering a solar wind from a small coronal hole
on the sun. Conditions could be unsettled on Friday and Saturday.
The projected planetary A index for Friday through Monday is 15, 15,
10 and 8. The projected solar flux for those same days is 120, 125,
125 and 130.

Several people wrote this week, including Larry, K0HNM and Tony,
K6BBC asking for information on propagation. Everyone seems to be
curious about what the numbers mean. As I've reported before, a
simple way to look at it is that HF operators would like the sunspot
activity to be high with the geomagnetic activity to be low.
Unfortunately, it often doesn't work that way, and high solar
activity can be accompanied by solar winds, which can disrupt or
disturb HF propagation.

I did suggest K9LA's discussion of basic propagation and what the
numbers mean. It is on the ARRL Technical Information Service web
page devoted to propagation at
http://www.arrl.org/tis/info/propagation.html. Past propagation
bulletins also have information and some interesting web links, and
an archive is at http://www.arrl.org/w1aw/prop/ . The A index and K
index express geomagnetic stability or instability, with the K index
measured every three hours and the A index expressed once per day.
They are on different scales, and the relationship between the two
is explained at http://www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html . A
web page explaining how sunspot numbers are derived is on the same
site at http://www.ngdc.noaa.gov/stp/SOLAR/SSN/ssn.html .

Another useful tool is propagation prediction software, and a good
free one is W6ELprop, available at http://www.qsl.net/w6elprop/ .
With this program you can plug in different dates, times,
frequencies, locations and solar flux values, and see what band is
likely to be open when and to where.

Sunspot numbers for December 26 through January 1 were 62, 63, 70,
51, 44, 50, and 47, with a mean of 55.3. 10.7 cm flux was 127.4,
116.5, 116.9, 114.8, 113.8, 115.1, and 115, with a mean of 117.1.
Estimated planetary A indices were 15, 37, 19, 13, 15, 11, and 10,
with a mean of 17.1.
NNNN
/EX