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The K7RA Solar Update


This week several new sunspots appeared for five days, but they were all leftover spots from Solar Cycle 23, not new Cycle 24 spots. But this is okay, because at the sunspot minimum we appreciate any spots we can get. May 16-20 saw daily sunspot numbers of 34, 23, 30, 28 and 23. Sunspot numbers for May 15- 21 were 0, 34, 23, 30, 28, 23 and 0 with a mean of 19.7. The 10.7 cm flux was 71.1, 71.6, 71.2, 71.6, 68.9, 68.6 and 69.1 with a mean of 70.3. Estimated planetary A indices were 4, 4, 2, 3, 8, 10 and 13 with a mean of 6.3. Estimated mid-latitude A indices were 2, 3, 1, 2, 5, 7 and 9, with a mean of 4.1.

Keep in mind that a sunspot number of 34 does not mean there were 34 sunspots last Friday. Instead, the numbers represent a somewhat arcane calculation that accounts for the number of sunspot groups and the size of each group. The count gets 10 points for each sunspot group and one point for each spot within the groups, the designation of these different areas within the groups seeming somewhat arbitrary to a layman such as myself.

So 34 could mean that there are three darkened areas, with one of them counting as two spots, the other two just one each. Presumably, the same number would describe the Sun with two darkened areas facing Earth, and each counting for seven spots. Thirty plus four is the same as 20 plus 14, but this week there were three areas.

For at least a couple of weeks the US Air Force and the NOAA Space Weather Prediction Center (SWPC) forecast a planetary A index of 25 for May 21, but on May 20 the prediction was downgraded to 15. The actual planetary A index for that day was 13, while the mid-latitude A index was 9; Alaska's College A index, taken near Fairbanks, was 19. The earlier number was based on an expectation of returning coronal holes and solar wind streams that proved to be weaker than expected.

Currently they expect quiet geomagnetic conditions and another prediction for a planetary A index of 25 just before the start of summer on June 17. Geophysical Institute Prague calls for unsettled conditions May 23-24, quiet to unsettled May 25, quiet May 26, quiet to unsettled again on May 27-28 and unsettled for May 29.

This weekend is the CQ WW WPX CW Contest, and of course, we don't expect any sunspots, but we don't expect disruptions either. Using a technique known as helioseismic holography, the Solar and Heliospheric Observatory's Michelson-Doppler imager detected a high latitude sunspot on our Sun's far side on May 17. If it doesn't fade away first, perhaps we may see that still hidden spot slip into view next week.

Right now we are in the main Sporadic E-skip season, and we have reports. Mike Shaffer, KA9JAW, of Tampa, Florida, regularly sends reports of television DX, and sends video and audio recordings as well. He has been receiving the Dominican Republic on channel two at 2230-2315 UTC, and a Canadian channel from Toronto, about 1100 miles from his home.

Jon Jones, N0JK, of Wichita, Kansas, documented nine 6 meter contacts between KH7Y, south of Hilo on the western side of the island of Hawaii, on May 19. He noted that the best propagation seemed to be to Iowa and Illinois.

David Fisher, KA2CYN, of New City, New York (up the Hudson River from Manhattan, on the west side) said there was a nice opening on 10 meters to the West Coast on May 16; around 2110 UTC he talked to K6CJA in California.

A good source for information on propagation can be found in any edition of The ARRL Handbook for Radio Communications, or even any of the old Radio Amateur's Handbook editions going back many years. Each has a chapter devoted to propagation, which is a good basic introduction. Also, this Flash slide-show is quite good at explaining the fundamentals.

Another good source is, Bob Brown's, NM7M, book, The Little Pistols Guide to HF Propagation. Unfortunately, it has long been out of print, but some local libraries may have it. My home library in Seattle has several copies -- in fact, I have one checked out right now. There is a PDF version available that you can download from K6PKL's Web site.

I shouldn't forget the excellent material from Carl Luetzelschwab, K9LA, on his Web site. Carl, the former editor of NCJ, is quite an expert on propagation and has been an invaluable resource for this bulletin.

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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