QST de W1AW
Propagation Forecast Bulletin 3 ARLP003
From Tad Cook, K7VVV
Seattle, WA January 21, 2000
To all radio amateurs
SB PROP ARL ARLP003
ARLP003 Propagation de K7VVV
Solar flux was up, geomagnetic activity was down. What could be better for HF propagation? Average solar flux this week was up 35 points, or over 20 percent, compared to the previous week. Geomagnetic conditions were quiet, with A indices in the single digits. The most stable day was January 17, when the planetary A index was 3 and the K index was 1 during five of the eight daily K index reporting periods. There also was a 3-hour period when the K index was 0.
During periods of heightened geomagnetic activity the higher latitudes always get hit worse. When the bands are rough in the lower or mid-latitudes, they often are unusable in places closer to the poles, such as Alaska. This is reflected in higher K and A indices at higher latitudes. But on January 17, the geomagnetic indices measured in Alaska (referred to as the College index) were actually lower than at lower latitudes, with five of the eight periods showing a K index of 0, and two periods at 1. The College A index for that day (Monday) was 2. It really doesn't get better than that.
While one would expect the best of conditions with numbers such as this, KK5CA in Texas wrote to say that he experienced a high noise level over the weekend. Since the numbers were so low, his suspicion is that he and other hams in the area were hearing local atmospheric noise stimulated by warm dry air and a steady wind.
Solar flux has been rising, and reached a short term peak on Sunday with a 2000z measurement of 207.7 and a 2200z reading of 209.6. It has mostly been falling since, dropping to 178.6 on Wednesday and 170.7 on Thursday. The outlook for this weekend is a continued decline in flux, with values of 170, 165 and 160 for Friday through Sunday. The predicted planetary A indices for the same three days are 12, 35 and 12. Saturday's geomagnetic conditions could prove interesting for this weekend's ARRL January VHF Sweepstakes. The reason for the predicted high geomagnetic activity is a class M3 solar flare on Tuesday, and an accompanying coronal mass ejection. The energy from this event is predicted to have maximum effect on Saturday, so expect poor HF radio conditions and possible aurora enhanced VHF propagation.
After the weekend look for solar flux to decline to around 135 for the period from January 27 through February 1, then rise above 150 around February 5 and peak again above 200 around February 11 and 12. Expect unsettled geomagnetic conditions from January 27 through the end of this month, with the worst conditions on January 27 and 28.
Sunspot numbers for January 13 through 19 were 218, 228, 268, 262, 227, 185 and 196 with a mean of 226.3. 10.7 cm flux was 202, 201.3, 210.7, 207.7, 196.4, 194.6 and 178.6, with a mean of 198.8, and estimated planetary A indices were 10, 7, 5, 6, 3, 4 and 4, with a mean of 5.6.
Path projections for this weekend are for Sunday from Dallas, Texas, but the other ends of the paths are all taken from this week's ARRL DX Bulletin, ARLD003.