rjr@mgweed.UUCP (Bob Roehrig) (09/25/84)
qst de k9eui hr propagation forecast bulletin nr 39 from arrl headquarters newington ct september 24, 1984 to all radio amateurs bt solar flux levels of 75 or lower september 13 to 20 almost exactly duplicate a significant low in april 1977, less than a year from the end of cycle 20. looking back to september 1975 shows flux high, low and average values to have been very similar to those of september 1984 thus far. these comparisons suggest that cycle 21 could be shorter than the 11.2 year average, but flux records available (garble) show that cycles 18, 19 and 20 all had brief periods of substantial sunspot activity in their final two years of life. we may be on the verge of such a burst. though visible sunspot activity has been very low for the last two weeks, there is action on the sun currently. a major geomagnetic storm, in progress as this bulletin was being prepared, narrowed the useable frequency spectrum severely. things may be better soon. the solar region now facing us brought a flux rise to 93 four weeks ago. such levels in late september and in early october could work wonders for 21 and 28 mhz which could last through about october 5. american sunspot numbers for september 13 through 19 were between 0 and 1 with a mean of 0.1 ar
rjr@mgweed.UUCP (Bob Roehrig) (10/02/85)
qst de k9eui hr propagation forecast bulletin nr 39 from arrl headquarters newington ct september 30, 1985 to all radio amateurs bt with one day to go as this bulletin was prepared, the solar flux average for september is 69.6. this will not change significantly when the flux reading for the 30th is added. we will then have our first monthly average under 70 since july 1976, the start of cycle 21. the present calm spell began august 11, when a nine year low of 67 was recorded. the flux has been no higher than 73 since, and there have only been 3 of these. more important, there were 26 days under 70 in the past 2 months including one 66 and six at 67. several short lived sunspots appeared several times but the most recent visible spot activity of any consequence came in late july. some solar emissions that cause fluctuations in the earths magnetic field and increased attenuation of hf signal levels in the higher latitudes cannot be seen in the conventional white light view of the sun. thus the sunspot record is not a completely reliable indicator for hf propagation prediction. the very erratic hf conditions of late september were typical, with about 5 periods of 1 to 2 days each of very good and very bad propagation, following one another in rapid succession. there will be more of this in october, after some fairly consistent good times early in the month. it is believed that the almost total absence of sunspots recently is a temporary phenomenon, probably not an indicator of an early end of cycle 21. the best 8 weeks of the year are at hand, in any case. american sunspot numbers for september 19 through 25 were between 0 and 10 with a mean of 3.4 ar