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The K7RA Solar Update


The average daily sunspot numbers for the week were up more than nine points to 35, and average solar flux rose more than six points to 87.3. These differences compare the dates of December 2-8 with the previous seven days. The average planetary A index declined 2.5 points to 2.1, while the average mid-latitude A index dropped 1.1 points to 1.6. These are nice numbers, with higher sunspot numbers accompanied by lower geomagnetic indices. Sunspot numbers for December 2-8 were 32, 27, 48, 47, 35, 34 and 22, with a mean of 35. The 10.7 cm flux was 86.5, 86.8, 87.4, 87.9, 88.5, 87.1 and 87.2, with a mean of 87.3. The estimated planetary A indices were 3, 1, 1, 1, 2, 4 and 3, with a mean of 2.1. The estimated mid-latitude A indices were 1, 0, 1, 0, 3, 3 and 3, with a mean of 1.6.

The predicted solar flux for the near term is right near or slightly above the average for the past week, at 87, 87, 88, 88, and 88 for December 10-14. The predicted planetary A index for December 10-14 is 8, 10, 10, 8 and 5. The planetary A index is expected to remain around 5 from December 15-24. Geophysical Institute Prague has a slightly different prediction for the next seven days: they predict unsettled conditions for December 10-11, quiet to unsettled December 12, unsettled December 13, quiet December 14 and quiet to unsettled December 15-16.

Note the period of somewhat unsettled geomagnetic activity centers around this weekend, the dates for the ARRL 10 Meter Contest, December 11-12, but only a mild increase in geomagnetic activity is expected. The Geminid meteor shower peaks December 13-14 and could provide some ionized trails enhancing 10 meter propagation. This year’s 10 meter contest is the first time that Mexican states will be counted as multipliers along with US states and Canadian provinces, as well as DXCC countries. You can see a map of the 32 Mexican states here.

Ten meters offers many opportunities for working Mexico from other North American locations this weekend. For instance, Distrito Federal, which includes Mexico City, should be workable from Salt Lake City from 1730-1900 and possibly from 1700-2100. The path from the San Francisco Bay Area looks even better, with the possibility of strong signals from 1700-2130. From the Chicago area, a likely opening is 1700-1830, possibly open as early as 1630 and as late as 2000. From Ohio, the path looks good 1630-1930, extending possibly 30 minutes early and an hour later. From Winnipeg, Manitoba (VE4), the possibilities look excellent at 1730-1900, very good 1630-2030 and possibly extending to 1600-2100z.

If you want to use the predicted smoothed sunspot number with a propagation prediction program for this month or next, you can find the latest predicted values in the table on page 11 in issue PRF-1840 here. The values are updated there about every 4 to 5 weeks. You can also do a peek into the future, as this table shows a predicted smoothed sunspot number for December 2010 of 38, 74 in December 2011 and 89 in December 2012. You can download W6ELprop here and run several instances of the program at once, flipping back and forth to compare projections for 2010 with 2011 and 2012. The 10 meter possibilities expand dramatically during periods of higher solar activity.

During the weekend, the STEREO craft will surpass 97.95 percent coverage of the Sun. You can calculate an approximation of the coverage by looking here and noting the number at the bottom “Separation angle A with B.” When I look at this early Friday morning, the number is 172.234, which corresponds to about 97.84 percent coverage. Subtract the separation angle from 180, then divide by 360, subtract the result from 1 and multiply times 100. Or skip the subtraction from 1 to determine the percent gap in the coverage.

To calculate the coverage at some time in the future, use the STEREO Orbit Tool. Just use any date and time you want to test and use the same method described above. At some point in early 2011 -- after STEREO reaches 100 percent coverage -- the gap will begin to grow again, but this time on the earth-facing side of the Sun. The image will be filled in with data from the Solar Dynamics Observatory (SDO. In fact, the current STEREO image already uses SDO data for the Earth-facing side of our Sun, even though that may seem redundant. But this probably assures us that the transition to 100 percent coverage will be seamless.

Randy Crews, W7TJ, of Spokane, Washington, lives 231 miles almost directly east of my home in Seattle. He’s at the eastern end of Washington State, 15 miles from the Idaho border. Although his latitude is slightly lower than mine, the exact beam heading is slightly north of east at 89.3 degrees, instead of some fractional amount south. Why is this? Because the shortest path is via the great-circle route, and at 231 miles, it is far enough to put the path leaving my place just slightly north of east, even though he is at 47.6017 degrees north latitude and I am at 47.6693 degrees north latitude.

Randy has looked over his old station logs recently and has observations about the progress of Solar Cycle 24: “Most don’t realize how low we went in the Cycle 23/24 low. Previous cycles began with a sunspot number of 10-12. This cycle began with a sunspot number of about 1.5! Usually the cycle bottoms and picks right up within 12-13 months from the low. Not the case with Solar Cycle 24. This cycle has yet to see the solar flux above 100. By comparison, Solar Cycle 22’s official bottom was September 1986, and as early as April 1987, Solar flux values were above 100 on many days (about 6 months later). With Cycle 24 (if you measure from the low of the lows, July/August of 2008), we are past the two year point, measuring from October of 2009 (when the number of Solar Cycle 24 spots exceeded the old number of Solar Cycle 23 spots) we are out over a year. I am grateful for what we have thus far. The high bands are open (17 meters consistently), which is a nice improvement and the higher bands from time to time also, which is a huge step from the long dry spell in 2008; however, the bands have not really stepped into high gear. Flux values consistently above 100 (years 2004/2005) would really move us into the fast lane.”

Thanks, Randy!

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 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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