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 Previous: FCC Announces New Universal Licensing System Interface |  Next: Surfin': A Free Lunch: Linux for Hams |
SEATTLE, WA, Dec 12, 2003--Declining sunspot numbers and high geomagnetic activity made for rough conditions this week. Average daily sunspot numbers for the week dropped by 57 percent from the previous week, and average daily solar flux was down by 34 percent. Average daily planetary A index more than tripled to 28.7.
Currently Earth is inside a high-speed solar wind. The interplanetary magnetic field points north, but geomagnetic conditions would be even more active if it pointed south. The wind is from a large coronal hole, and the stream began affecting Earth on December 8. No sunspots now face Earth. Sunspot 517 is leaving the visible solar disk, while Sunspots 520 and 521 are coming around the opposite limb.
The active region that caused the wild space weather in October and November is around sunspot 488, now crossing the sun's far side. Its return to the Earth-facing side should cause a rise in the sunspot and solar flux numbers. Solar flux is expected to stay below 100 until Tuesday, December 16, and then rise suddenly Thursday and Friday, December 18-19.
Unfortunately, conditions should be rough for the ARRL 10-Meter Contest this weekend. Predicted solar flux values for Friday through Monday, December 12-15, are 85, 90, 90 and 95. Predicted planetary A index numbers for the same period are 40, 35, 25 and 20.
Ten-meter paths really need a high MUF value to sustain them, and the low sunspot numbers we're seeing now don't help. You can get an idea how conditions might differ from past years by trying some historic numbers on the free W6ELprop program. For this weekend, a path from California to Cleveland (W6 to W8 in the program's atlas) using a flux of 90 and K index of 4 would yield a rather narrow opening, probably only reliable from 1800-1900 UTC. A path from Dallas to Brazil (W5 to PY in the atlas) shows a poor probability for a path (although Seattle to PY looks much better).
You can sample values from past bulletins on the ARRL Web site. Looking at Bulletin 53 from 2002, for example, the average solar flux for Friday through Sunday of the 10-meter contest weekend was 185. The K index must have been quite low that period, because planetary A indices were 7, 11 and 9. Using the flux value of 185 and a K index of 2, the California to Cleveland path looked fantastic from 1530 through 2330 UTC, and the other paths looked much better as well.
What a difference a year can make in a changing solar cycle!
Sunspot numbers for December 4 through 10 were 115, 88, 87, 53, 49, 23 and 46, with a mean of 65.9. The 10.7 cm flux was 115.8, 111.7, 108.9, 92, 93.7, 92.2 and 89.2, with a mean of 100.5. Estimated planetary A indices were 9, 43, 22, 15, 39, 31 and 42, with a mean of 28.7.
Amateur solar observer Tad Cook, K7RA,
Seattle, Washington, provides this weekly report on solar conditions and
propagation. This report also is available via W1AW every Friday and an
abbreviated version also appears in The ARRL Letter. Readers
may contact the author via k7ra@arrl.net.
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