QST de W1AW
Propagation Forecast Bulletin 7 ARLP007
From Tad Cook, K7VVV
Seattle, WA February 16, 2001
To all radio amateurs
SB PROP ARL ARLP007
ARLP007 Propagation de K7VVV
The quiet sun period continues, as the sunspot number dropped below 100 and solar flux went down to 137.9 on Wednesday. The last two times that solar flux values were this low were on December 9 and September 13 of last year. Average solar flux for the past week was down almost 15 points and average sunspot numbers were off by over 5 points, when compared to the previous week. The forecast for the next few days has solar flux dropping to 135 on Friday and Saturday, and bottoming out around 130 on Sunday and Monday. It is then expected to rise rapidly from 135 to 165 between February 21- 23.
Despite the relatively quiet sun, there was some geomagnetic activity this week. The earth entered a high speed solar wind stream on Tuesday, and the results were planetary A indices of 19 and 17 on Tuesday and Wednesday, with planetary K indices as high as 4 over much of the two days. The high latitude College A index was 24 and 26, and over a few periods the College K index was 5. This wind stream was probably the result of a coronal mass ejection that occurred on Sunday. Fortunately, the bulk of this ejected mass missed us, but there was enough to trigger some unsettled conditions as well as higher absorption of HF radio signals over polar paths.
Conditions should be relatively settled for the ARRL International DX CW Contest this weekend, and with the days getting a little longer, we should see a little more spring-like propagation on HF.
KA7TON wrote recently asking about the sun's magnetic poles reversing during the peak of every solar cycle. At the time I could not recall the details, but now there have been some news items on this subject over the past week. A story on a NASA web site at http://science.msfc.nasa.gov/headlines/y2001/ast15feb_1.htm says that the switch has already happened, and that this is a good indication that the peak of the solar cycle is here, or perhaps has passed. Apparently the earth's magnetic field also does this, but reversals are between five thousand and fifty-million years apart instead of every eleven. More info on solar magnetic fields can be found at http://science.nasa.gov/ssl/pad/solar/dynamo.htm.
Readers may also want to check the March 2001 issue of Worldradio magazine for the propagation column by K9LA. Carl writes about the 10.7 cm solar flux value, and how it may not be the best indicator for daily propagation conditions.
Now we will present a few path predictions for the DX contest this weekend. We will use a solar flux value of 145.5, which is average for the last seven days and the next three. These are good bets for when the bands should be open between average amateur stations. The West Coast location is centered on San Francisco, and the East Coast center is on Washington, D.C. Conditions will vary as you move away from these areas. For instance, in the West Coast 10 meter path projection to Europe, the prediction is for a possible opening around 1730z. Move north to Seattle, and this opening seems to disappear, but move south to Los Angeles, and it looks like a fairly good bet from 1700-1830z. The ones marked best are stable periods of what should be strong signals. Good luck in the contest.
Sunspot numbers for February 8 through 14 were 168, 179, 172, 169, 106, 113 and 99 with a mean of 143.7. 10.7 cm flux was 156.5, 162.4, 160.7, 151.3, 144.6, 141.3 and 137.9, with a mean of 150.7, and estimated planetary A indices were 6, 4, 5, 7, 4, 19 and 17 with a mean of 8.9.