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24 October, 2008
ARLP044
Visible sunspots continued last week for eight days straight, the longest continuous period of sunspot visibility since the twelve days of March 23 through April 3 2008.
For this week a solar wind stream is headed our way, and may strike October 28. The NOAA Space Weather Prediction Center places the predicted effect slightly later, with a predicted planetary A index for October 27 through 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 1930-2100z, 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 2300-0100z, and signals were a very strong 40 dB over S9.
Mack Beal, W1PNR of Jackson, New Hampshire asked about new Cycle 24 sunspots compared to sunspots from old 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. Go to the web site, http://sohowww.nascom.nasa.gov/data/realtime/realtime-mdi_mag-1024.html.
This site has an archive of recent images. 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, and the last four indicate time in UTC. There is a link at the very bottom called "List of all individual images" which 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, white on the left. It is tracking from left to right, and if this were below the equator, it would be an old Cycle 23 spot. But this sunspot is a Cycle 24 sunspot, and note that spots above and below the equator have opposite polarity. So a 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 and April 3 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 Cycle 23 spots appear, this must mean that Cycle 24 has started, unless we look over a longer time period and determine that Cycle 23 spots are not in the minority.
If you would like to make a comment or have a tip for our readers, email the author at, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL Technical Information Service web page at, http://www.arrl.org/tis/info/propagation.html.
For a detailed explanation of the numbers used in this bulletin see, http://www.arrl.org/tis/info/k9la-prop.html.
An archive of past propagation bulletins is at, http://www.arrl.org/w1aw/prop/.
Monthly propagation charts between four USA regions and twelve overseas locations are at, http://www.arrl.org/qst/propcharts/.
Instructions for starting or ending email distribution of this bulletin are at http://www.arrl.org/w1aw.html#email.
Sunspot numbers for October 16 through 22 were 24, 11, 0, 0, 0, 0, and 0 with a mean of 5. 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. Estimated planetary A indices were 4, 2, 1, 6, 2, 3 and 5 with a mean of 3.3. Estimated mid-latitude A indices were 5, 1, 1, 5, 2, 3 and 5 with a mean of 3.1.
Source: The
American Radio Relay League
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