QST de W1AW
Propagation Forecast Bulletin 15 ARLP015
From Tad Cook, K7VVV
Seattle, WA April 14, 2000
To all radio amateurs
SB PROP ARL ARLP015
ARLP015 Propagation de K7VVV
Solar activity was down over the past week. Average solar flux was off over 35 points and average sunspot numbers were down over 80 points, when compared with the previous week. Geomagnetic indices were way up at the beginning of the reporting week, with major storms on April 6 and 7 when the planetary A indices were 56 and 50. As the UTC day passed from Thursday to Friday, the K index was as high as 8, which is very disturbed.
N7GXD reported from Northern Utah that he worked a number of stations some distance away, including Colorado and Canada, on 6 meters using only 10 watts into a single quad loop. This was enhanced by aurora propagation on Thursday evening. You can read the MSNBC story on this aurora on the web at http://www.msnbc.com/news/392145.asp?0a=2347151.
Solar flux should reach a short-term minimum in the next few days. The predicted solar flux values for Friday through Tuesday are 165, 165, 160, 160 and 165. Flux values are expected to reach 200 by April 21, and peak near 225 around April 27. Predicted planetary A indices for the next five days are 10, 12, 7, 7 and 8. After this weekend the A index should stay in the single digits until April 26 through May 4, with a peak in unsettled to active geomagnetic conditions around April 29.
With somewhat lower solar flux and the passing of the spring equinox, the author has noted that 10 meter conditions may not be what they were a short time ago. As an example, on March 22, the solar flux at noon at the Penticton observatory was 233.8. Run these numbers in a popular propagation program, and it shows a strong path from Seattle to Hawaii on 10 meters, with good signals from 1800-0400z. But run the numbers for April 13, when the flux was 164, and the numbers are quite different. Now it shows an unreliable path covering the same period, but with much less chance of an opening.
If we pretend that April 13 had the higher solar flux of 233.8, the path does get more reliable, but nothing like the path right around the equinox. There is the possibility of a longer lasting opening on April 13, because there are more hours of daylight. If we run the numbers for a day right in between the two dates, which is April 2, we see values somewhere in between the two. The big difference is seasonal effects. For 10 meters, there is really no time like the equinox at the solar cycle peak for fabulous conditions.
Email received from several readers pointed out a couple of errors in the last bulletin, ARLP014. An unfortunate accident with a search and replace function changed every appearance of the number 10 to say 10 meters. Not all of these errors were caught and edited. VE3YE pointed out that the reference to solar flux of 343 on November 10 should have said sunspot number. Oh, if only the solar flux were that high.
If you ever have a comment, write to firstname.lastname@example.org.
Last week's bulletin also omitted a review of monthly and quarterly solar flux numbers, which we will examine here.
The average solar flux for the four quarters of 1999 were 136.7, 145, 157.6 and 175.2 . The value for the first quarter of 2000 was 180.5. This indicates the sort of upward progression expected as we move toward the peak of cycle 23. The average monthly solar flux for January through March was 159, 174.1 and 208.2, also a nice upward trend.
Sunspot numbers for April 6 through 12 were 155, 172, 167, 160, 175, 148 and 172 with a mean of 164.1. 10.7 cm flux was 177.7, 174.9, 182, 176.3, 177.8, 181.5 and 173, with a mean of 177.6, and estimated planetary A indices were 56, 50, 14, 13, 20, 10 and 5, with a mean of 24.
The path projections for this weekend are from Ohio.