QST de W1AW
Propagation Forecast Bulletin 6 ARLP006
From Tad Cook, K7RA
Seattle, WA February 6, 2004
To all radio amateurs
SB PROP ARL ARLP006
ARLP006 Propagation de K7RA
Sunspots are back in view. Last week's Propagation Forecast Bulletin ARLP005 reported two days with a sunspot number of 0, but this week the average daily sunspot number rose 28 points to 66.7. This is nice for short term HF propagation, but now that January has passed, a look at monthly averages shows a clear decline in the sunspot cycle.
The monthly average of daily sunspot numbers in January 2003 through January 2004 were 150.0, 87.9, 119.7, 114.3, 89.6, 118.4, 132.8, 114.3, 82.6, 118.9, 103, 75.7 and 62.3. Average daily solar flux values over the same months were 144, 124.5, 133.5, 126.8, 116.6, 129.4, 127.7, 122.1, 112.2, 155.5, 140.8, 116.1 and 114.1.
You can see that over the past 13 months average daily sunspot numbers dipped below 100 several times, but were never below 82.6 until December and January when they dropped to 75.7 and 62.3. Look for declining solar activity over the next few years, with the predicted bottom of the solar cycle still three years off.
Right now sunspot 551 is moving into the center of the visible solar disk, the place where sunspots have the most effect on earth. Geomagnetic conditions at mid-day today (Friday, February 6) were unsettled, but unless the active region around sunspot 551 spews forth, conditions should be normal over the next few days. The predicted solar flux over this weekend (February 6-9) is 105-110. Solar flux values should peak around 130 toward the middle of the month.
This week let's look at paths to Brazil, where it is currently late summer. We will look at 20 meters and above only.
For more information concerning 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 January 29 through February 4 were 25, 42, 49, 57, 106, 103 and 85 with a mean of 66.7. 10.7 cm flux was 87.4, 92.7, 94.4, 97.3, 101.5, 99.4 and 101.4, with a mean of 96.3. Estimated planetary A indices were 10, 17, 12, 11, 21, 17 and 15, with a mean of 14.7.