ZCZC AP21
QST de W1AW
Propagation Forecast Bulletin 21 ARLP021
From Tad Cook, KT7H
Seattle, WA May 23, 1997
To all radio amateurs
SB PROP ARL ARLP021
ARLP021 Propagation de KT7H
At last there is a bit of solar activity to report. There was a big geomagnetic upset at the start of the period, with a planetary A index of 53 on May 15. This indicates highly disturbed conditions, where absorption rather than reflection of radio waves is the rule, particularly over polar paths. It was caused by a parallel ribbon solar flare on May 13, and the resulting solar wind had a big effect.
Solar flux rose over this week, and peaked at 84.8 on Wednesday. This week was the first time in awhile that the daily flux has risen above the 90 day average of 74.
W4VOS sent a nice letter regarding the recent lack of activity. He mentioned the news item from propagation bulletin ARLP003 in January which talked about an American Astronomical Society meeting in Toronto, where scientists from Yale and NASA said that this next solar cycle should show a decrease in overall activity compared to previous cycles.
He also noted in his letter that after the last solar minimum in 1986, activity jumped right back, and there was no question that the new cycle was on a roll. This time there is a much longer period of low activity between cycles.
Currently there is wide disagreement between experts on when higher activity will resume, and by how much. As an example, NOAA and the National Geophysical Data Center's estimates for the sunspot count for June vary by four to one.
20 meters remains the best band for worldwide propagation during daylight hours.
Sunspot Numbers for May 15 through 21 were 15, 27, 47, 32, 51, 57 and 79 with a mean of 44. 10.7 cm flux was 73, 72.2, 72.8, 74.1, 74.2, 79.1 and 84.8, with a mean of 75.7, and estimated planetary A indices were 53, 12, 12, 6, 4, 6, and 5, with a mean of 14.