ZCZC AP51
QST de W1AW
Propagation Forecast Bulletin 51 ARLP051
From Tad Cook, K7VVV
Seattle, WA December 18, 1998
To all radio amateurs
SB PROP ARL ARLP051
ARLP051 Propagation de K7VVV
Solar activity was mixed this week, with sunspot numbers up an average of about 10 and solar flux down about 9 points compared to last week. The average solar flux for the previous 90 days rose from 131 to 132, and solar flux was above this level on every day, a good indicator of a general upward trend. The active geomagnetic day was Friday, when the Planetary A index rose to 30 and the College, or high latitude A index was 52. This indicated a geomagnetic storm.
Conditions were good for last weekend's 10 Meter contest, even with the rough conditions at the start. Solar flux was higher than forecast, with the Friday through Sunday numbers at 143.1, 143.3 and 144.2, rather than the predicted 132, 128 and 122.
This bulletin is written on Thursday, and geomagnetic conditions have been exceptionally quiet, with an A index of 0. The Boulder K index was also 0 throughout the day, and the College and Planetary K index only showed marginal activity around 1500 and 1800z. Over the next three days, Friday through Sunday, the predicted Planetary A index is 9, and the solar flux should be around 145, 140 and 135.
Beyond the weekend expect the solar flux to rise back to 150 around December 28 and 29, then drift below 145 again on the last day of the year, rising slightly again the second week in January. Look for slightly unsettled conditions around December 28 and 29.
There were some interesting conditions on VHF this past week. On December 11, while the geomagnetic storm was disrupting propagation on HF, ZL3SIX in Christchurch was hearing many North American stations on 6 Meters, including N5JHV and two Mexican beacon stations. Also, VK3AMK worked TI5KD and SM0KAK/XE1 worked VK7GK on 6 Meters. On 2 Meters, WA6TBO heard the KH6HME beacon, and WP4O reported working Uruguay from Puerto Rico.
Sunspot Numbers for December 10 through 16 were 145, 166, 142, 152, 113, 108 and 118 with a mean of 134.9. 10.7 cm flux was 133.8, 143.1, 143.3, 144.2, 144.4, 141.6 and 140.5, with a mean of 141.6, and estimated planetary A indices were 6, 30, 6, 3, 4, 5 and 11, with a mean of 9.3.