QST de W1AW
Propagation Forecast Bulletin 6 ARLP006
From Tad Cook, K7VVV
Seattle, WA February 7, 2003
To all radio amateurs
SB PROP ARL ARLP006
ARLP006 Propagation de K7VVV
Sunspot numbers dropped way down into the double-digits this week, and compared with last week the average daily sunspot number was off by nearly 51 points. Daily solar flux values declined last week and then rose this week, so the average daily value for the week was practically unchanged at less than two points higher. Solar flux is expected to peak through next week around 170, with predicted daily values for Friday through Sunday at 155, 160 and 165.
Geomagnetic conditions were quite active this week, with the average daily planetary A index up over 8 points from last week. A solar wind stream caused some high A and K index values, with the peak day on Sunday when the planetary A index was 45 and K indices were as high as 6, indicating a geomagnetic storm. Higher latitudes were even more affected, and Alaska's College A index reach 58. This made higher latitude HF communications more difficult. Moderate geomagnetic conditions are predicted for the next few days, but Monday could be unsettled.
January has passed, so let's look at the average daily solar flux and sunspot numbers for the month to spot any trends.
Average daily sunspot numbers for August 2002 through January 2003 were 191.0, 206.4, 153.9, 159.8, 144.8 and 150.0. Average daily solar flux for those same months was 183.9, 175.8, 167.0, 168.7, 157.2 and 144.0. This shows a downward trend. For the next 45 days the predicted average daily solar flux is 140.3. For the same 45 days last year the actual daily solar flux averaged 188.8, so going into the spring, MUFs (Maximum Usable Frequencies) should be lower and general HF conditions a bit poorer. But during the same period in 2001 the average daily solar flux was 147.3, only seven points higher than the values predicted for the next month and a half. If predicted values hold up (keeping in mind that forecasting out 45 days is chancy) conditions going into spring at least may not be worse than 2001.
Pick a date a few weeks from now (in the middle of the 45 day period mentioned above) and plug it into a popular propagation prediction program. Then compare the 140.3 value for this year with 188.8 for last year. This may give us some idea of how spring conditions might be compared to last year. For instance, if I plot a path for March 1 from Texas to Brazil, 15 meters closes about four hours earlier in 2003 compared to 2002, and 10 meters closes about an hour and a half earlier. I ran these numbers using W6ELprop, available free at http://www.qsl.net/w6elprop/.
For more information about 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 and, especially, the article "The Sun, the Earth, the Ionosphere," by Carl Luetzelschwab, K9LA.
Sunspot numbers for January 30 through February 5 were 105, 96, 75, 61, 69, 77, and 89, with a mean of 81.7. 10.7 cm flux was 121.2, 120.4, 125.8, 126.7, 132.5, 134.8, and 140.1, with a mean of 128.8. Estimated planetary A indices were 26, 18, 13, 45, 19, 24, and 12, with a mean of 22.4.