ZCZC AP41
QST de W1AW
Propagation Forecast Bulletin 41 ARLP041
From Tad Cook, K7RA
Seattle, WA October 10, 2003
To all radio amateurs
SB PROP ARL ARLP041
ARLP041 Propagation de K7RA
In last week's bulletin we looked at the weekly averages for daily solar flux and sunspot numbers and reported that both had risen, from 92 to 125 for sunspots and 119 to 133.6 for solar flux. This week it has dropped lower than it was two weeks ago. The average daily sunspot number was 86.7, and the average daily solar flux was 115.8. This week also represents the second in a row in which geomagnetic indices have dropped, indicating a quiet and stable Earth environment for HF radio propagation.
Currently we are within a solar windstream, but a north- pointing interplanetary magnetic field keeps geomagnetic activity to a minimum. Current projections from the US Air Force show stable geomagnetic conditions over the next few days, with planetary A index around 10 from October 10-12. Following this weekend on Monday, it shows planetary A index rising to 30 for October 13-14.
The forecast from Frantisek Janda, OK1HH, shows quiet geomagnetic conditions on October 10, quiet to unsettled conditions on October 11-12, unsettled to active on October 13, and unsettled again on October 14 and 15. Predicted solar flux from the Air Force is 105 for October 10-11, 100 for October 12, and 95 for October 13-14. Following this is a rise in solar flux, passing 110 around October 16, 120 on October 18, 130 on October 21, and 135 on October 25-26. These are rough estimates based upon the last solar rotation.
The 10-10 Day Sprint is today, October 10 (UTC). As we move toward winter, 10 meters will be less useful. If you use a propagation prediction program such as W6ELprop, compare projected 10-meter conditions this weekend with projected 10-meter conditions for September 23. You can see that 10 meters already is closing a little earlier than at the equinox. To test the seasonal propagation variation further, try running the same tests for the weekend of the ARRL 10- Meter Contest, which is December 13-14. You can download W6ELprop free.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site.
Sunspot numbers for October 2 through 8 were 75, 104, 89, 101, 93, 76 and 69, with a mean of 86.7. The 10.7-cm flux was 124.8, 120.1, 119, 109.6, 112.1, 111.9 and 113.3, with a mean of 115.8. Estimated planetary A indices were 9, 16, 9, 9, 10, 13 and 9, with a mean of 10.7.