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The K7RA Solar Update


While solar activity weakened this past week, geomagnetic conditions were stable. The geomagnetic storm predicted for last weekend did not happen, and both the planetary and mid-latitude A index only rose to 10 on April 14 in response to a glancing blow from a coronal mass ejection (CME). The average daily sunspot numbers declined nearly 25 points to 113.3, while the average daily solar flux was down more than 17 points to 121.7. Sunspot numbers for April 11-17 were 121, 128, 148, 111, 99, 97 and 89, with a mean of 113.3. The 10.7 centimeter flux was 137.1, 137.9, 125.1, 116.8, 113.3, 113.3 and 108.1, with a mean of 121.7. The estimated planetary A indices were 5, 5, 6, 10, 5, 3 and 3, with a mean of 5.3. The estimated mid-latitude A indices were 4, 4, 6, 10, 6, 2 and 2, with a mean of 4.9.

For the near term, the predicted flux values are 95 on April 19, 90 on April 20-23, 95 on April 24-25, 100 on April 26, 110 on April 27-28, 115 on April 29-30, 120 on May 1-2, 125 on May 3-6, 120 on May 7-8, and down to 115 for May 9-12. The predicted planetary A index is 5 on April 19-22, 12 on April 23-25, 15 on April 26, 5 on April 27 to May 4, 8 on May 5, 5 on May 6-11, and rising to 8 on May 12.

Paul Drahn, KD7HB, of Crooked River Ranch, Oregon, wrote: “I must take exception to your comment about ‘great news for HF propagation.’ We’re having a hard time on our local evening nets on 75 meters. I am active on the Oregon Emergency net on 3.980 MHz from 6-7 PM each evening. The Tennessee phone net also operates on the same frequency, just prior to our net starting. After their net, several Tennessee hams use the frequency as a local rag chew net. At times, such as the last two evenings, they are stronger in Oregon than many of the local check-in stations. Last night, there were at least three conversations going on from Tennessee, all on 3.980 MHz; they could not hear each other, and we could not hear the OEN. We expect this interference in the winter, but it is only a problem at other times when the propagation allows it. Fortunately, the folks in Tennessee go to bed early!”

As we move later in the spring and toward the summer, the signals should be weaker around net time. It might help if the folks in Tennessee used an NVIS-type antenna for local coverage, since these antennas don’t have a low angle of radiation. There are several pages that describe Near Vertical Incident Skywave (NVIS) antennas, such as or or

All times listed are UTC, unless otherwise noted.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here and here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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