QST de W1AW
Propagation Forecast Bulletin 15 ARLP015
From Tad Cook, K7VVV
Seattle, WA April 9, 1999
To all radio amateurs
SB PROP ARL ARLP015
ARLP015 Propagation de K7VVV
Solar activity perked up a little bit this week, with average solar flux rising almost 15 points to 118.9 and average sunspot numbers up over 40 points to 89.6. The reporting week (which runs from Thursday through Wednesday) began with unsettled geomagnetic conditions, and a planetary A index of 14. One year ago the average sunspot numbers were 89.4, about what they were this week, and average solar flux was 121.8, 10 points higher than this week.
K6UJ wrote to ask about A and K indices and what they mean. This is a frequently asked question. The K index is updated every three hours, and you can hear the latest number on WWV at 18 minutes after the hour, or hear it any time by telephone at 303-497-3235. The K index is a measure of geomagnetic instability, and the higher the number, the greater is the absorption of radio signals, especially over polar paths. A one point change in K is a big change. Every day there is a new A index, and it is based on the K index for the previous 24 hours. A one point change in the K index results in a large change in the A index.
If the K index is 0 for all eight reporting periods in a day, then the A index is 0. If the K is 1, the A is 3, if it is 2, the A is 7, if K is 3, the A is 15, if K is 4, the A is 27, if K is 5, the A is 48, if K is 6, the A is 80, if K is 7, the A is 180, if K is 8, the A is 240, and if the K is 9 for 24 hours then the A is 400. Of course, it is rare for the K index to be the same value for all eight 3-hour periods in a day, and so the A comes out to be something between the numbers given above. For instance, on April 1 when the planetary A index was 14, this was the result of K readings of 5, 5, 2, 2, 2, 2, 1 and 1.
Among other mail this week was a humorous letter from N6TP showing a correlation between the solar flux and his employer's stock price. He showed this to his fellow telephone company employees on April 1.
Several letters also arrived remarking on the disappointing sunspot and solar flux numbers, which many feel should be higher given that we are one year away from the predicted peak of cycle 23. W2LO noted that he has been watching the numbers since cycle 19 in the 1950s, and he feels something is wrong. W8GF sent similar sentiments, and wondered if this cycle peaked last December. KH6BZF was asked for comments, and noted that after a cycle peak there are many solar flares, and this has not happened yet. He also said he feels that this cycle has not hit the high solar phase yet.
For this weekend, look for a solar flux of 140, 139 and 135 for Friday through Sunday, with a planetary A index of 10, 10 and 8 for those same days. Beyond the weekend look for the solar flux to drop below 130 after April 15, below 120 a few days later, bottoming out below 115 from April 23-25. It should rise above 120 after April 29, and to 130 by May 4. Look for active geomagnetic conditions around April 25, continuing with unsettled conditions through May 1.
Sunspot Numbers for April 1 through 7 were 59, 50, 77, 90, 111, 119 and 121 with a mean of 89.6. 10.7 cm flux was 103, 99.5, 102.7, 115.9, 132.6, 137.4 and 141.4, with a mean of 118.9, and estimated planetary A indices were 14, 10, 8, 13, 11, 9 and 9, with a mean of 10.6.
The path projection for this week is from Southern California: