The K7RA Solar Update


Solar activity was quiet this week: The average daily sunspot number declined nearly 23 points to 90.6, while the average daily solar flux values were down nearly 13 points to 109.1. The most active day was April 24, with a planetary A index of 19 and mid-latitude A index of 15. The average daily mid-latitude A index was the same this week as last, 4.9. Sunspot numbers for April 18-24 were 86, 101, 101, 76, 83, 95 and 92, with a mean of 90.6. The 10.7 centimeter flux was 105, 99.4, 104.9, 109.3, 112.9, 117.5 and 114.7, with a mean of 109.1. The estimated planetary A indices were 3, 2, 4, 3, 4, 7 and 19, with a mean of 6. The estimated mid-latitude A indices were 2, 1, 2, 3, 5, 6 and 15, with a mean of 4.9.

The predicted solar flux is 120 on April 26-29, 125 on April 30 through May 1, 130 on May 2-3, 125 on May 4-5, 120 on May 6, 115 on May 7-8, 120 on May 9-11, 115 on May 12-13, 110 on May 14-15, 105 on May 16-18, 110 on May 19 and rising to 120 on May 20. The predicted planetary A index is 12 on April 26, 5 on April 27-May 4, 8 on May 5, 5 on May 6-18, and rising to 8, 12, 12, 15, 12 and 5 on May 19-24.

At 0503 UTC on April 26, Australia’s Ionospheric Prediction Service issued a geomagnetic disturbance warning, calling for increased geomagnetic activity due to a high speed solar wind stream from a low-latitude coronal hole. Minor storm levels are possible; active-to-minor storm levels are expected April 26, while unsettled-to-active levels are expected April 26-27.

Bob Logan, NZ5A, lives in Manor, a tiny town in Central Texas. On Sunday, April 14 at 2032, he was surprised to work HC2UA in Ecuador on 6 meter CW with 4 W. His antenna was unusual, an 80 meter inverted V with the center at 35 feet, fed with ladder line and an HF antenna tuner, which Bob said “is not designed to tune 6 meters, but it does!” He also worked HC2UA again at 2043 UTC on SSB, although they were not able to copy his report. “Quite exciting for me!” said Bob.

Jeff Hartley, N8II, of Shepherdstown, West Virginia wrote on April 19: “Ten and 12 meters have been quite poor with the recent solar activity decline, but 15 and lower continue to delight, with 20 meters open to western Europe and the Middle East through most, if not all of their night. There were tremendous signals on 10 meters from South Central and Southeastern Europe during the recent flux in 140s, the best days being April 10 and 11. The highlight of propagation was working VK9CZ in Cocos-Keeling on 10 CW easily around 1400 UTC I had a run of Japanese stations on 12 meter SSB, with the loudest signals over S9.”

Scott Bidstrup, TI3/W7RI, sent an article about a study that is using a pair of sounding rockets to see if turbulence in the E-region of the ionosphere at sunset could serve as a warning of disturbance in the F-layer one to two hours later.

NASA has a new video of the Sun that shows three years of continuous images. In that time, if the Sun rotates relative to Earth about every 27.5 days, this video should show 398 rotations of the Sun, in fewer than four minutes.

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.