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 Previous: German School Group Enjoys Successful ARISS Contact |  Next: Surfin': Yet Another Television Inventor |
SEATTLE, WA, Dec 19, 2003--What could be better than a rising sunspot count and declining geomagnetic activity? If it were a couple of years ago, we could enjoy more sunspots. But considering the stage of this solar cycle, HF conditions are good and have even improved over the past few days.
During the comparable week in 1999, the average daily sunspot number was around 132. In 2000 it was 186. In 2001, it was 200. Average planetary A index for all those weeks was less than 10.
This week, sunspot numbers have risen (42, 71, 92 and 114 for December 15-18). Over the same four days, the planetary A index has dropped (25, 11, 10, 8) along with the mid-latitude A index (18, 9, 4, 2). We don't often see this combination. When the sun cooperates and shows expanding sunspots, raising the MUF, we often get space weather that disturbs Earth's geomagnetic field and the ionosphere, raising absorption of HF signals and wreaking havoc with propagation. Now, with the modest rise in sunspots, we have declining geomagnetic indices, a welcome combination.
Over the next few days conditions are likely to change. By Sunday, December 21, Earth should meet a solar wind generated by a coronal hole. Predicted planetary A index for this weekend is between 15 and 20, but it should quiet down in the following days. Solar flux for this weekend is predicted at around 135, and flux values should rise to a peak around 140 by December 22-23. Solar flux may drop below 100 by the New Year.
If geomagnetic indices go low after the weekend and sunspots increase, we should see improved HF conditions, although for the northern hemisphere Monday will have the least sunlight of any day of the year. This means slightly lower average MUF values than were seen a few weeks earlier, if all other factors were equal. A forecast from the Prague Geophysical Institute shows December 24-25 as the quietest geomagnetic days over the next week.
Andy Cohan, AB0YT, is a student in physics and astronomy at the University of Iowa and president of the UI Radio Club, W0IO. A friend of his is doing a research project for which she needs geomagnetic K index data for the past five years. I pointed him toward the Service International des Indices Geomagnetiques (International Geomagnetic Service Index) Web site, which contains data going back to 1868. Plots of planetary K index values going back several years are at on the Space Environment Center FTP site.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site.
Sunspot numbers for December 11 through 17 were 35, 36, 40, 48, 42, 71 and 92, with a mean of 52. The 10.7 cm flux was 86.1, 87.2, 87.8, 92.4, 100.8, 106.3 and 117.5, with a mean of 96.9. Estimated planetary A indices were 40, 23, 28, 24, 25, 11 and 10, with a mean of 23.
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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