ARRL

ARRL Propagation Bulletin ARLP035 (2000)

SB PROP @ ARL $ARLP035
ARLP035 Propagation de K7VVV

ZCZC AP35
QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7VVV
Seattle, WA  September 1, 2000
To all radio amateurs 

SB PROP ARL ARLP035
ARLP035 Propagation de K7VVV

Solar activity was generally lower over the past week, with average
solar flux down by over seven points and sunspot numbers down by
nearly 28 points, compared to the previous week.

Naturally, since we are at or near the peak of this solar cycle,
there is some worry that we may have already passed the peak, and
solar activity may be headed down.  Of course we won't know this
until many months after the peak, when we can look at running
averages of the previous numbers.  Fortunately, solar cycles seem to
decline more slowly than they rise, so if conditions have peaked, we
shouldn't expect any sharp decline anytime soon.

The latest projections from NOAA show the solar flux peaking in
September and sunspot numbers reaching maximum around December.
About once per month NOAA shows a projection at
http://www.sec.noaa.gov/weekly/index.html , which you can see if you
have an Adobe Acrobat reader.  Select the latest Preliminary Report
and Forecast of Geophysical Data, and page to the end of the report.
Once per month there is a table showing past and projected smoothed
sunspot numbers, followed by one showing solar flux values.  The
last weekly edition showing this table is dated August 8, so perhaps
next week's will show an updated table as well.

The average monthly solar flux for August, 1999 through August 2000
was 170.8, 135.7, 164.8, 191.5, 169.8, 159, 174.1, 208.2, 184.2,
184.5, 179.8, 200.5 and 163.1.  This shows that the average solar
flux for August was not only lower than August of last year, but was
the lowest value since January of this year.  The highest average
monthly solar flux was in March, 2000, although July was not much
lower.

I am not sure when they made the change, but you really should check
out the new home page for the NOAA Space Environment Center at
http://www.sec.noaa.gov/index.html .  The new layout and graphics
are quite impressive.

W9OL wrote to ask why 10 meters seems less reliable than last year,
even though the solar flux was lower in 1999.  He also remarked that
often the path to South American is open (he lives in Illinois) but
signals to Europe and Asia are poor.  This is probably because with
more solar activity there have been more solar flares and coronal
holes, resulting in more geomagnetic activity.  The result is poor
radio paths over the polar regions, and some north-south
enhancements.  There is some evidence that higher geomagnetic
activity does not really enhance trans-equatorial or north-south
propagation, but signals over the equator appear to be enhanced by
comparison because signals over the polar region are so degraded.

In last week's bulletin, a link to Solar and Heliospheric
Observatory images via a webcam site was mentioned.  NR0A wrote to
say that a better link titled The Very Latest SOHO Images is at
http://sohowww.nascom.nasa.gov/data/realtime-images.html .

For the next few days, expect geomagnetic indices to settle down,
and conditions to be generally quiet.  The next active period, based
on the previous solar rotation is September 6-8.  Another active
period is possible around September 25-26.  Look for solar flux to
decline slightly over the next few days to around 161 on September
3-4, then rising to around 185 on September 8.  Expect fairly good
propagation for the All Asia DX Phone Contest this weekend, with
fairly quiet geomagnetic conditions and progress toward the autumnal
equinox.

Sunspot numbers for August 24 through 30 were 92, 101, 104, 124,
165, 175 and 187 with a mean of 135.4. 10.7 cm flux was 130.6,
133.2, 137, 150.1, 160, 163.3 and 164.8, with a mean of 148.4, and
estimated planetary A indices were 10, 7, 9, 9, 21, 31 and 13 with a
mean of 14.3.
NNNN
/EX