ZCZC AP23
QST de W1AW
Propagation Forecast Bulletin 23 ARLP023
From Tad Cook, K7RA
Seattle, WA June 4, 2004
To all radio amateurs
SB PROP ARL ARLP023
ARLP023 Propagation de K7RA
The sun appears nearly blank, with one small spot, Sunspot 621, facing Earth. There are no other noticeable areas of activity, however. Just two days ago there were several more sunspots, but they are no longer visible. These sunspots didn't rotate off the visible disk but just faded from view.
Sunspot numbers and solar flux are understandably quite low. Average daily sunspot numbers for the May 27 through June 2 period was nearly 40 points lower than the daily average for the previous seven days. Over the same period, average daily solar flux was down almost seven points. Fortunately, geomagnetic activity was low. Over the weekend conditions were unsettled, but otherwise several days had mid-latitude geomagnetic A indices in the single digits.
Over the next week expect low geomagnetic activity. Planetary A index for June 4-8 is expected at 10, 8, 8, 10 and 10. Solar flux values for the same days are predicted to be 90, 95, 95, 100 and 100. Solar flux is expected to peak between June 11-16 around 110.
Now that May is over, we should look at some monthly trends over the last year. The monthly average of daily sunspot numbers for May 2003 through May 2004 was 89.6, 118.4, 132.8, 114.3, 82.6, 118.9, 103, 75.7, 62.3, 75.6, 81, 59.3 and 77. The monthly average of daily solar flux for the same 13 months was 116.6, 129.4, 127.7, 122.1, 112.2, 155.5, 140.8, 116.1, 114.1, 107, 112.1, 101.2 and 99.8. Solar flux hit a new monthly low during May for this downward side of the solar cycle when it dropped below 100.
We're in a late spring propagation mode now. Higher HF bands, such as 10 and 12 meters, are seeing fewer openings, although this month we should see sporadic E skip. As the days grow longer, absorption during daylight hours should increase. Daytime propagation on 20 meters won't be as good as it was a few months ago, but late night propagation should improve. Also during the summer, seasonal noise levels increase--probably more noticeably on 160, 80 and 40 meters. Forty meters should still be good for some long- distance nighttime propagation, however.
Field Day is still a few weeks off, but currently the SEC 45 Day AP forecast for planetary A index shows unsettled conditions predicted for the June 26-27 weekend, with A values of 15. This is really too early to tell, but the picture of conditions for that weekend should become clearer as we approach the date.
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page.
Sunspot numbers for May 27 through June 2 were 62, 52, 57, 64, 54, 76 and 63, with a mean of 61.1. The 10.7 cm flux was 101.8, 102.4, 101.2, 99.6, 95.4, 90 and 90.4, with a mean of 97.3. Estimated planetary A indices were 6, 9, 14, 13, 14, 16 and 11, with a mean of 11.9. Estimated mid-latitude A indices were 5, 6, 12, 11, 11, 14 and 9, with a mean of 9.7.