QST de W1AW
Propagation Forecast Bulletin 15 ARLP015
From Tad Cook, K7VVV
Seattle, WA April 12, 2002
To all radio amateurs
SB PROP ARL ARLP015
ARLP015 Propagation de K7VVV
Sunspot numbers and solar flux rose again this week. Average daily sunspot numbers for April 4-10 were up nearly 40 points, and average daily solar flux rose by more than 11 points, when compared with the seven-day period that ended April 3.
Solar flux is expected to decline over the short term--to below 190 after this weekend, and below 180 after next Wednesday. There is a chance of geomagnetic unrest this weekend due to a solar flare and coronal mass ejection on April 10 at 1230 UTC. This wasn't aimed exactly at Earth, so the effects are a little hard to predict, but Thursday morning's forecast from the US Air Force has the planetary A index at 12 on Friday, 15 on Saturday and 20 on Sunday.
We got mail this week via firstname.lastname@example.org. N2YQZ wrote from Eastern New York to comment that over the past few weeks he has noticed more frequent dead times on 10 meters, particularly around sunrise.
N0JK reported that on April 6, K4SUS in Florida worked Japan, Taiwan and China on 6 meters, all via long path. N0JK also worked LU1YBB in Argentina around 1904 UTC on April 3 from Kansas via F2 layer propagation on 6 meters. He reports that more seasonal north-south propagation on 6 meters is noted around this time of year, particularly from the southern tier of the United States. He says that peak times are around early afternoon.
KD2FT wrote to say he reads this bulletin via email, and plans to take an extended cruise in his boat this fall. He wants to get basic solar flux and geomagnetic alerts via HF radio. Best to tune into WWV at 18 minutes after each hour or to WWVH at 45 minutes past the hour. WWVH is on Kauai in Hawaii, and broadcasts on 2.5, 5, 10 and 15 MHz. WWV is in Fort Collins, Colorado, and is on 2.5, 5, 10, 15 and 20 MHz. Of course the precise time service from these stations also is useful if you need to set an old style ship's chronometer.
N0YD wants to know, in a nutshell, how the numbers reported in this bulletin will affect propagation. He would like to know if conditions will get better or worse, or when we can expect radio blackouts. A good place to look for an explanation is K9LA's piece on the ARRL Web site, but N0YD would like a shorter summary of the upcoming week in each bulletin.
Well, basically, on HF we like to see lots of sunspots (or high solar flux) and very low geomagnetic activity, as reported in K and A indices. This past week had very low geomagnetic activity, so that was good. The fact that solar flux was higher over the past week is generally good, although it really takes a big movement in the numbers to have a noticeable effect.
There is a possibility for higher geomagnetic activity this weekend, and that might be bad for high frequency propagation, partly because of increased absorption. But it could be good for VHF in terms of auroral propagation, where you can bounce your VHF signals off of an aurora by aiming your antenna north. Solar flux is expected to be slightly lower next week, but not enough to make a big difference.
Ten, 15 and 20 meters will be the focus this weekend for the Japan International HF CW DX Contest. Stations outside of Japan will score points by working Japanese stations. Here are a few path projections for this weekend from various locations. Polar paths to Japan could have a rough time if the K index is above 3.
Sunspot numbers for April 4 through 10 were 176, 200, 234, 227, 245, 212 and 220, with a mean of 216.3. The 10.7-cm flux was 216.2, 217.4, 206.3, 207.9, 206.2, 205 and 194.3, with a mean of 207.6. Estimated planetary A indices were 8, 6, 5, 7, 5, 6 and 7 with a mean of 6.3.