ZCZC AP39
QST de W1AW
Propagation Forecast Bulletin 39 ARLP039
From Tad Cook, K7VVV
Seattle, WA September 24, 1999
To all radio amateurs
SB PROP ARL ARLP039
ARLP039 Propagation de K7VVV
This week was a big disappointment for HF radio enthusiasts. Last week's Propagation Forecast Bulletin, ARLP038, stated that on Thursday, September 23, the solar flux should be around 220. This was the date of the autumnal equinox, generally a peak time for HF propagation. Unfortunately the sunspots did not materialized and the solar flux for the day was over 80 points lower than predicted.
Not only have solar flux and sunspot numbers been lower than expected, but geomagnetic disturbances were prevalent as well. Wednesday was the most active period, when the planetary A index was 37.
What's next? Currently the flux is around 137 as this is being written on Thursday, and the predicted values for Friday through Sunday are 135, 135 and 130. Predicted planetary A index is 15, 12 and 10. Beyond the weekend the best guess is for solar flux to go below 130 after September 27 and bottom out around 110 on October 5. Flux values are not expected to rise above the current level until October 11, and peak around 160 by mid-month.
Active geomagnetic conditions could reappear around October 4 and again around October 9 and 10.
Despite the disappointing numbers, the author of this bulletin has had fun this week on HF mobile. Abandoning the usual 17 meter operation, 10 and 15 meters were tried, and consistent contacts with loud signals from Japan during the afternoon commute were made after 2300z above 21.3 MHz SSB.
Sunspot numbers for September 16 through 22 were 153, 144, 152, 113, 78, 82 and 103 with a mean of 117.9. 10.7 cm flux was 158.2, 157.5, 151.6, 149.3, 145, 146.8 and 140.4, with a mean of 149.8, and estimated planetary A indices were 32, 15, 16, 10, 10, 10 and 37, with a mean of 18.6.
Path projections for this week are from Birmingham, Alabama.