ARLP034 Propagation de K7RA:
August 20, 2004

Propagation Forecast Bulletin 34 ARLP034
From Tad Cook, K7RA
Seattle, WA August 20, 2004
To all radio amateurs

ARLP034 Propagation de K7RA

Solar flux and sunspot numbers rose this week. August 13-14 were the peak days for both, and with low and stable geomagnetic indices, HF conditions were good. There weren't any days with notable geomagnetic upsets.

Sunspot 649 has rotated off the western limb of the sun, and on August 18 it emitted a large coronal mass ejection. Since it is facing away from earth, we are not likely to be affected, but from a right angle the mass thrown off the sun from this region is more visible than if the spot were facing us. Right now sunspot 652 is pointed in our direction, and there are some spots identified on the sun's far side using the helioseismic holography method.

Geomagnetic indices are expected to rise, then decline again over the next few days. The expected planetary A index for August 20-23 is 15, 12, 10 and 12. The expected solar flux for the same days is 115, 110, 105 and 100.

We are only a month away from the Fall equinox. Of course this will bring the good Fall conditions to HF. Due to the declining solar cycle, it probably won't be as good as Fall was over the past few years, but should be better overall for the higher bands than summertime was.

For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page at,

Sunspot numbers for August 12 through 18 were 140, 160, 111, 98, 68, 63 and 53 with a mean of 99. 10.7 cm flux was 147.2, 148.6, 149.2, 138.8, 133.6, 135 and 139.9, with a mean of 141.8. Estimated planetary A indices were 9, 9, 9, 7, 8, 11 and 13, with a mean of 9.4. Estimated mid-latitude A indices were 6, 5, 6, 3, 5, 9 and 10, with a mean of 6.3.