QST de W1AW
Propagation Forecast Bulletin 35 ARLP035
From Tad Cook, K7RA
Seattle, WA August 29, 2003
To all radio amateurs
SB PROP ARL ARLP035
ARLP035 Propagation de K7RA
Sunspot counts were up this week, but so were geomagnetic indices. Average daily sunspot numbers rose 33% over last week and the average daily planetary A index was up 18%. Solar flux remained about the same. This week didn't have an extremely stormy day, such as August 18 last week, but the higher A indices were sustained through the week. Active geomagnetic conditions declined through the week, with the most active days August 21-23 (our reporting week runs Thursday through Wednesday). The active days started August 21 because that is when the earth entered a high-speed solar wind, which continued over the next few days.
The moderate conditions should continue through this weekend. The latest reading predicts a planetary A index of 12 for August 29-31, Friday through Sunday. Monday has a predicted planetary A index of 10, but Tuesday, September 2 may become active again, based upon recurring conditions from the previous rotation of the sun. Solar flux is expected to remain around 125 through September 1, and then rise gradually to around 135 for September 3-4.
The days are getting shorter, and soon it will be the fall DX season, bringing better conditions. The higher frequencies should be opening during the day and 80 and 40 meters will open earlier and more reliably after dark. As an example, over the path from California to Japan, a month ago 10 meters offered no reliable communication. Currently 10 meters may have an opening on some days from around 2100-0430z. But around the equinox, the same California to Japan path on 10 meters looks quite good, with much stronger signals and reliable openings from 2130 to 0130z.
On the new 60 meter band from California to Georgia, a month ago signals were very strong from sundown on the west coast until sunrise at the east end. Strongest signals would be from 0400-1030z, with reasonable openings as early as 0130 and as late as 1230z. Currently the strongest signals should run from around 0330-1100z, with possible openings from 0030-1300z. Around the third week in September, strongest results should be from 0300-1100z, with openings generally good from 0000-1330z. September will also have much lower atmospheric noise on the lower frequencies.
One caveat about the equinox. During this phase of the solar cycle, although HF propagation should be better, there is also a greater chance of severe geomagnetic storms and aurora. This is because around late September the interplanetary magnetic field near earth tips far to the south. This makes the earth vulnerable to solar wind. For more on the interplanetary magnetic field and how it affects geomagnetic conditions, see http://spaceweather.com/glossary/imf.html.
For more information on propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at http://www.arrl.org/tis/info/propagation.html.
Sunspot numbers for August 21 through 27 were 86, 126, 125, 132, 146, 124, and 116, with a mean of 122.1. 10.7 cm flux was 119.2, 120.9, 120.2, 116.4, 116.5, 120.8, and 125.7, with a mean of 120. Estimated planetary A indices were 53, 43, 44, 24, 21, 14, and 13, with a mean of 30.3.