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SEATTLE, WA, Jul 27, 2001--It's summertime, but not too early to look forward to fall HF radio conditions. F-layer propagation should return to 10 and 12 meters in the fall, particularly for those operating in the higher latitudes. The summer solstice was on June 21 this year, and the autumnal equinox will be September 22. This places the mid-way point between the longest day and the equinox about 10 days from now.
Not many sunspots are currently visible, and a holographic image of the far side of our star shows no substantial sunspot groups. Average daily sunspot numbers over the past week dropped 10 points, and average solar flux was down just over two points. Solar flux values have been meandering, and this is expected to continue.
Solar flux values over the next week should be flat, around 120 from July 28 through August 2. Solar flux could gradually rise after that, but not much of a peak is expected, unless new activity develops. The holographic image of the sun's far side gives us a hint of things to come, since any activity exactly opposite from our view should be back on earth side in about two weeks.
Although there hasn't been much sunspot activity, we have recently been affected by a high speed solar wind emitted from a coronal hole. This accounts for the planetary A index of 15 and 22 on Tuesday and Wednesday. Current forecasts show the planetary A index dropping to around 12 on Friday and below 10 on Sunday, then possibly rising to around 15 on Tuesday and Wednesday.
Sunspot numbers for July 19 through 25 were 180, 193, 153, 153, 143, 143 and 96, with a mean of 151.6. The 10.7-cm flux was 142.3, 142.6, 139, 140.4, 143.2, 132.5 and 133.3, with a mean of 139. Estimated planetary A indices were 9, 8, 8, 11, 12, 15 and 22 with a mean of 12.1.
Amateur solar observer Tad Cook, K7VVV Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version also appears in The ARRL Letter. Readers may contact the author via k7vvv@arrl.net.
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