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The K7RA Solar Update


The average daily sunspot numbers hardly changed from last week and the week prior, but the average daily solar flux bounced back to about the level it was from two weeks ago: The average daily sunspot numbers were down 5 points to 50.7, while the average daily solar flux was up 7.7 points to 106.4. Sunspot numbers for January 31-February 6 were 47, 65, 54, 79, 30, 41 and 39, with a mean of 50.7. The 10.7 centimeter flux was 102.7, 103.7, 111.8, 111.1, 106.7, 105.1 and 103.5, with a mean of 106.4. The estimated planetary A indices were 1, 4, 9, 4, 4, 2 and 2, with a mean of 3.7. The estimated mid-latitude A indices were 1, 4, 9, 6, 3, 2 and 2, with a mean of 3.9.

The predicted solar flux values are 105 on February 8-10, 110 and 105 on February 11-12, 100 on February 13-14, 110, 115 and 110 on February 15-17, 115 on February 18-19, 110 on February 20-21, 105 on February 22, 115 on February 23-24, then 110, 105 and 100 on February 25-27, 95 on February 28-March 2, 115 on March 3-4, 120 on March 5-6, and rising to 125 on March 7-8. The predicted planetary A index is 22, 15 and 10 on February 8-10, 5 on February 11-18, 8 on February 19, 5 on February 20-21, then 15, 10 and 8 on February 22-24, 5 on February 25-28, 10 and 8 on March 1-2, 5 on March 3-7, and rising to 8 on March 8-9.

I’ve been looking at the predictions for planetary A index and solar flux, and it is interesting to note how they change over time. The planetary A index prediction for February 3 for more than a month was a value of 5 until January 31, when it changed to 18. Then on February 1-2, it was 15, but on February 3, the actual value was 4. A similar thing happened with the February 4 prediction -- it was 5 up until January 31, when it changed to 15. On March 1-2, it was 12, then it changed back to 15 on March 3. The following day, March 4, the actual value was 4 again, just as it was the day earlier.

On February 7, the planetary A index prediction for February 8 is 22, and on February 6 the prediction for February 8 was 8; prior to that it was 5. We will see the actual value at the end of the day today, February 8.

We heard from Fabrizio Valdirosa, a shortwave listener in Italy, who inquired about the average sunspot number for all of 2011. We mentioned recently that it was 29.9, but Fabrizio thought this was too low while looking at the monthly averages. I recalculated by again totaling all of the daily sunspot numbers for 2011, which is 29,239. Divide that by 365 days, and we get an average daily sunspot number for that year of 80.1. I have no idea how 29.9 was previously calculated, except that I somehow came up with a total for the year of 10,913 instead of 29,239 and it was my own error. So the average yearly sunspot numbers for 2008-2012 were 4.7, 5.1, 25.5, 80.1 and 82.3.

Don Street, HS0ZEE, wrote to ask about seasonal variations mentioned in the bulletin: “Here in Asia, spring and fall are not so well defined. Perhaps for readers like me, it would be helpful to mention which month you refer to.” We are just referring to the seasons as the time between equinox and solstice, and solstice to equinox. This page gives the dates for the seasonal changes. Don -- who also likes the HAP charts for HF propagation that are produced by the Australian government – noted that he finds the charts give “near-to-actual band conditions. Unfortunately, they are based on the previous hours observed conditions, but still very useful.”

Bill Bliss, W1WBB, of Portsmouth, Rhode Island, wrote: “I don’t believe I’ve seen these two new forecast products from the SWPC mentioned in your weekly column. I found via a link on their home page. They are issued twice daily and I’ve found them helpful as an additional tool for predicting near-term propagation on the HF/MF amateur bands. Links for feedback on both the 3-day forecast and the forecast discussion are also provided. Positive feedback on these ‘experimental’ products from the amateur community (accepted up through February 12) may help ensure they become a permanent part of SWPC’s Data and Products area.”

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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