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.