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The K7RA Solar Update

10/24/2008

Visible sunspots continued last week for eight days straight, the longest continuous period of sunspot visibility since the 12 days of March 23April 3 last year. Sunspot numbers for October 16-22 were 24, 11, 0, 0, 0, 0 and 0 with a mean of 5. The 10.7 cm flux was 71.9, 70, 69.2, 69.6, 69.2, 68.8 and 67.7 with a mean of 69.5. The estimated planetary A indices were 4, 2, 1, 6, 2, 3 and 5 with a mean of 3.3. The estimated mid-latitude A indices were 5, 1, 1, 5, 2, 3 and 5 with a mean of 3.1.

This week, a solar wind stream is headed our way, and may strike October 28. The NOAA Space Weather Prediction Center (SWPC) places the predicted effect slightly later, with predicted planetary A index for October 27-November 1 at 5, 8, 12, 15, 10 and 5. Geophysical Institute Prague predicts quiet conditions for October 24, quiet to unsettled October 25, quiet October 26-27, quiet to unsettled October 28, unsettled to active October 29 and unsettled October 30. Both predictions place the disturbance between this weekend's CQ Worldwide SSB DX Contest (October 25-26) and the ARRL CW Sweepstakes a week later.

Vince Varnas, W7FA, of Portland, Oregon, reports that on Sunday October 9 at 1930-2100 UTC, 10 meters was open to Latin America. He worked (I assume on phone) Brazil, Uruguay, Argentina, Honduras and Costa Rica, mostly with S9 signals. This is a bit late in the season for sporadic-E skip, and this was two days after the recent run of sunspots. Vince believes he is too far north for trans-equatorial propagation and that it must have been via the F2 layer.

The day before, Francisco Chubaci, PU2MLC, of Sao Paulo, Brazil, received a very strong 6 meter signal on October 18 from NP4A in Ponce, Puerto Rico. This was between 2300-0100 UTC -- signals were a very strong 40 db over S9.

Mack Beal, W1PNR, of Jackson, New Hampshire, asked about new Solar Cycle 24 sunspots compared to sunspots from old Solar Cycle 23. He heard they change polarity, but wants more detail on how this is determined. Yes, they do change polarity. We can see this by looking at magnetograms of the Sun. Below the top section is a list of individual images for the current month. The leading characters in the filename represent year, month and day; the last four indicate time in UTC. There is a link at the very bottom called "List of all individual images" that leads to an archive for the whole year.

You can look at images from October 10-17 to see that string of recent sunspots. If you click on the "10-15-2008 0941z" file, you can see a big spot in the northern hemisphere with black on the right and white on the left and is tracking from left to right. If this was below the equator, it would be an Solar Cycle 23 spot. But this sunspot is a Solar Cycle 24 sunspot -- note that spots above and below the equator have opposite polarity. So a Solar Cycle 23 sunspot north of the equator would have black on the left and white on the right.

Go back to the list page and click on the "List of All Individual Images" link on the bottom of the page so we can see spots between March 23-April 3 that are mentioned at the top of the bulletin. Note that these spots are black on the right like the recent spots, but it is difficult to tell which side of the equator they are on, so the cycle status may be indeterminate. The new cycle is said to begin when there are more new cycle spots than old, but I have no idea over what time frame. If we look at only the spots from last week, since no Solar Cycle 23 spots appear, this must mean that Solar Cycle 24 has started, unless we look over a longer time period and determine that Solar Cycle 23 spots are not in the minority.

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 in The ARRL Letter. 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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