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The K7RA Solar Update


Tad Cook, K7RA, of Seattle, Washington, reports: We saw plenty of sunspot activity this week, along with numerous solar flares. A confounding indicator was a higher average solar flux but lower average sunspot numbers. We expect to see these parameters track together, but that isn’t always the case.

The average daily sunspot number went from 87.4 last week to 74.6 in the latest reporting period, March 10 – 16.

The average daily solar flux increased from 115.5 to 119.

A new sunspot group appeared on March 12, another on March 13, and two more on March 14. The total sunspot area (expressed in millionths of the solar disc) declined throughout the week, starting at 1,170 on March 10, then 1,080, 1,040, 940, 670, 490, and 290. So, the decline continued even through days that revealed new sunspots.

March 13 had the greatest geomagnetic disturbance, with the middle latitude A index at 30, the planetary A index at 40, and Alaska’s college A index at 65. The A index is calculated from the K index, updated every 3 hours. In Alaska, the K was 0 in the first three readings, at 0000, 0300, and 0600 UTC, before jumping dramatically to 5, 7, 7, and 5 for the rest of the day. The K index is logarithmic, and 7 is a very big number, indicating a geomagnetic storm.

The solar flux prediction peaks at 125 on April 6 – 8, but starting today, the predicted flux is 108 on March 18 – 19; 95 on March 20 – 26; 100 on March 27 – 28; 110 on March 29 – 30; 115 on March 31; then 120, 115, and 120 on April 1 – 3; 115 on April 4 – 5; 125 on April 6 – 8; 120 on April 9 – 11; 115 on April 12 – 14; 110 on April 15 – 17; 100 on April 18; then 95 on April 19 – 22, and 100 on April 23 – 24.

Predicted planetary A index is 10 on March 18 – 19; then 15, 12, and 8 on March 20 – 22; 5 on March 23 – 25; 10 and 8 on March 26 – 27; 5 on March 28 – 30; 10, 25, 15, and 8 on March 31 – April 3; 5 on April 4 – 15; 12 on April 16 – 17; 8 on April 18; then 5 on April 19 – 21, and 10 and 8 on April 22 – 23.

The vernal equinox will occur at 1533 UTC on Sunday, March 20 — a good sign for HF propagation as we move from winter to spring conditions in the Northern Hemisphere.

From F.K. Janda, OK1HH:

“Undoubtedly, the most dramatic phenomenon of the past 7 days was the arrival of a CME [coronal mass ejection] on March 13, which broke away from the sun on March 10 – 11. It caused a medium [G2] geomagnetic storm. In its positive phase, [MUF] values increased during the UTC afternoon until evening, while the overall ionospheric propagation of decameter waves improved overall. In the negative phase that followed on March 14 – 15, they deteriorated significantly. A return to normal has been observed since March 16.

“A CME could do more than just ignite the bright aurora borealis. It also lowered the level of cosmic rays. A neutron monitor at the Sodankylä Geophysical Observatory in Oulu, Finland, saw a sharp decline in cosmic rays shortly after the CME arrived. It’s called the ‘Forbush Decline,’ named after the American physicist Scott Forbush, who studied cosmic rays in the early 20th century. It happens when a cloud of coronal matter pushes galactic cosmic rays away from our planet. The cosmic rays fell sharply on March 13, then rose sharply at noon on March 14, then fell sharply again. We attribute this fluctuation to the more complex structure of the CME cloud. The cosmic rays remained depressed for 2, partly to 4, days after the arrival of the CME.

“The consequences of the coming of a CME in Earth’s magnetosphere and ionosphere were now, near the vernal equinox, more pronounced than they would have been at any other time of year.”

I (K7RA) was experimenting with FT8 and PSKreporter on Friday, March 11, on 10 meters and noticed at 2145 UTC that my low-power signal (with a very modest antenna) was heard over a narrow arc running from northern Virginia and central Texas, plus reports from two stations in New Zealand and several in South America. Fifteen minutes later, the only report was from K1HTV in Virginia. By 2224 UTC, the only reports were from two local western Washington stations, at 4 and 54 miles away.

On March 15, using the same setup on 10 meters at 1651 UTC, the only station outside the local area hearing me was XE1ACA, 2,344 miles away.

Often when coverage is marginal on 10 meters, 12 meters will be open.

At 1730 UTC on 12 meters, I was heard over a broad arc of stations 1,800 – 2,400 miles away, running from New Hampshire to south Texas, plus XE2BCS and XE1GK at 1,757 and 2,003 miles, and NH6Y in Hawaii at 2,654 miles. That arc of coverage was only 600 miles wide.

On March 14, VE1VDM reported unstable 10-meter conditions. “As of 1600 UTC [1 PM local] today, I have not had one RBN report on 28.173 MHz, nor one WSPR report on 28.126.130 MHz,” he said. “The band has really tanked here in Nova Scotia.”

Jon Jones, N0JK, reported on March 13:

“Larry, N0LL (EM09), decoded a number of South American stations on 50.313 MHz FT8 around 0040 UTC March 13. These included CE3SX (FF46), CE0YHF/CE3, CE2SV, and LU5FF. Larry was away from the radio when this occurred. [I] suspect an Es link to TEP [transequatorial propagation]. He then worked XE2TT (DL44) on Es at 0117 UTC. I monitored during this time frame. No South [American stations were contacted], but [I] did decode K3VN (EL98) around 0050 UTC on Es.”

Also from Jon on the same day:

“A rare March sporadic-E opening on 6 meters [occurred on] the afternoon of March 11, from Kansas to W1, W2, W3, and W8.

“Here in Lawrence, I worked K3ISH (FN21) and KE8FD (EN80) on 50.313 MHz FT8 around 2100 UTC, [and copied] a few others.

“WQ0P (EM19) was in a better spot for it. He worked W1, W2, W3, W4, and W8.

“No rare DX, but any sporadic-E opening in March is noteworthy. The month of March has the lowest occurrence of sporadic E of any month of the year (see:

“If the Es cloud had been located to the southeast [there could have been] a potential link-up with afternoon TEP. [I] did not see anyone working South America.”

A tribute to Maunder — of Maunder Minimum fame — and his wife, “Astronomer couple honoured with English Heritage blue plaque,” appeared in the UK’s Oxford Mail.

David Moore sent this obituary of pioneering astronomer Eugene Parker — “Eugene Parker, astrophysicist namesake of NASA’s Parker Solar Probe, dies at 94” — which appeared in

Check out the latest video from Tamitha Skov, WX6SWW, the Space Weather Woman.

Sunspot numbers for March 10 – 16 were 90, 81, 93, 64, 82, 71, and 41, with a mean of 74.6. The 10.7-centimeter flux was 127.1, 126.5, 124.7, 122.9, 114.9, 110.4, and 106.6, with a mean of 119. Estimated planetary A indices were 10, 20, 13, 40, 14, 7, and 5, with a mean of 15.6. Middle latitude A index was 7, 15, 7, 30, 13, 5, and 3, with a mean of 11.4.

For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check this propagation page by Carl Luetzelschwab, K9LA.

A propagation bulletin archive is available. Instructions for starting or ending email distribution of ARRL bulletins are on the ARRL website.

For customizable propagation charts, visit the VOACAP Online for Ham Radio website.

ARRL member Tad Cook, K7RA, has been writing the weekly ARRL Propagation Bulletins since 1991. Share your reports and observations.



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