ZCZC AP18
QST de W1AW
Propagation Forecast Bulletin 18 ARLP018
From Tad Cook, K7VVV
Seattle, WA April 30, 1999
To all radio amateurs
SB PROP ARL ARLP018
ARLP018 Propagation de K7VVV
Solar flux and sunspots were down again this week, although with activity so low, it couldn't really drop very far. Solar flux has taken a jump in the past couple of days, with solar flux up about 20 points on Thursday compared to earlier in the week. The predicted solar flux for this weekend, Friday through Sunday is 125, 130 and 135, and the Planetary A index is predicted at 25, 30 and 30. The geomagnetic field has been active for the past few days due to coronal holes, and this should continue.
Beyond the weekend, higher solar flux should continue, with values around 140 or higher. Solar flux is expected to drop down to around 125 again by May 11, and 110 a week later.
Jim Secan of Northwest Research Associates (www.nwra.com) wrote to emphasize that when we notice this solar cycle in a stall, it is important to keep in mind that when we are comparing it with past cycles, we are often looking at smoothed charts with moving averages. Jim says that it is not at all unusual for a solar cycle to stall like this, and in fact cycle 19 of the late 1950s, fondly recalled by radio amateurs as the biggest solar cycle of all time, did this as well. Predicting solar cycles is based upon statistical observations but without very many cycles to base it on. Jim says that the latest revised forecast from the NOAA Space Environment Center puts the peak of the cycle probably around late 2000. Since the peak of any cycle is really spread over a couple of years, fixing a particular season and year is probably not realistic.
I received a couple of nice notes from Shel Shallon, W6EL, author of the popular Mini Prop propagation software, and from Orlando, KT4KF. They both pointed out that solar flares and coronal mass ejections are not the same. A solar flare releases particles which may cause a coronal mass ejection, and if it is strong enough, the ejection can hit earth, which a flare never does. Shel mentioned that a coronal mass ejection may contain a billion tons of matter and travel at several million miles per hour. Coronal mass ejections may also appear independently of flares.
K0FF wrote that on Wednesday he worked many South American stations on six meters from Northeast Missouri. This was during a period when the geomagnetic conditions were unsettled, but not active or stormy.
Sunspot Numbers for April 22 through 28 were 62, 71, 89, 69, 69, 82 and 76 with a mean of 74. 10.7 cm flux was 100.2, 98.2, 100.9, 102.6, 104.5, 108.6 and 109.8, with a mean of 103.5, and estimated planetary A indices were 4, 5, 7, 5, 7, 14 and 19, with a mean of 8.7.
The path projection for this weekend is from Hawaii.