This past week, the average daily sunspot numbers were up 16.2 points to 101.1, while the average daily solar flux remained about the same, rising from 118.5 to 119. An eruption on March 15 caused a coronal mass ejection (CME) that hit Earth on March 17, causing the planetary A index to jump to 46. Sunspot numbers for March 14-20 were 133, 105, 90, 126, 116, 68 and 70, with a mean of 101.1. The 10.7 centimeter flux was 122.8, 123.1, 126, 125.7, 117.6, 110.4 and 107.6, with a mean of 119. The estimated planetary A indices were 5, 6, 10, 46, 7, 5 and 9, with a mean of 12.6. The estimated mid-latitude A indices were 4, 5, 8, 32, 6, 4 and 7, with a mean of 9.4.

The predicted solar flux is 105 on March 22, 100 on March 23-27, 105 on March 28, 100 on March 29-30, 105 on March 31, 110 and 120 on April 1-2, 125 on April 3-6 120 on April 7-8, 115 on April 9, 110 on April 10-11, then 105, 100, 120, 115 and back down to 110 on April 12-16. The planetary A index is predicted to be 8 on March 22-23, 5 on March 24-26, 12 on March 27-28, 10 on March 29, 5 on March 30-April 16, and rising to 8 on April 17.

Jack Kelley, K4WY, of Fairfax Station, Virginia, wrote about an unusual experience on a seemingly dead band this past Sunday: “I had some interesting propagation in the wake of the CME last weekend. After checking the bands (160-10), the only station I found was 5T0JL in Mauritania at S9 on 30 meters -- we worked each other easily, and after listening to Jean’s following QSOs, I found he was working W6s almost exclusively. Again, there was no other signal, anywhere. So how did this occur? The path was assumed to be east-west and in darkness, but all the W6 QSOs stumped me, particularly after the worst of the CME effects. A similar scenario happened with 6V7S in Senegal later that same evening as he plowed through the extremely high static.”

This was Sunday night local time, or 0130-0200 UTC Monday. I ran this by Carl Luetzelschwab, K9LA, who indicated that the path through low latitudes was the key to success: “The effects from elevated K indices due to a CME include modification to the worldwide F2 region ionization. Generally, the mid and high latitudes see a depletion of electrons, whereas low latitudes aren’t affected too much (or even see an enhancement).”

Carl ran some numbers using the Space Weather Prediction Center STORM model and noted that in both hemispheres, “the F2 region ionization was depleted significantly around 0200 UTC on March 18. But the ionization at low latitudes in both hemispheres fared much better. Additionally, was there perhaps some ‘spotlight’ propagation going on? Could be. The ionosphere is very dynamic, especially under disturbed conditions.”

The day after the big blast, The New York Times ran an interesting article on solar flares and the possible effects on the power grid, satellites and communications.

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.