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The K7RA Solar Update


With the appearance of two sunspots, the past 11 days had some nice HF propagation. Combined with quiet geomagnetic conditions and month after month of quiet Sun, it seems quite a dramatic relief. Sunspot 1026 has faded away, and sunspot 1027 -- which appeared later than 1026 but actually led it in the Sun's rotation -- has just rotated out of view, over the Sun's western limb. You could see this early Friday morning by viewing the STEREO animation.

Remember that the 0 degree meridian is facing us and the two 90 degree longitudinal marks are at the Sun's eastern and western horizons. It seems odd, since we are accustomed to viewing an atlas with west on the left and east to the right, but when we say a sunspot is rotating over the western limb, it is moving to the right, from our point of view.

Early Friday morning (evening on the West Coast in North America), you could see that northern heliosphere bright spot just beyond the +90 degree mark. There is a bright spot in the southern heliosphere where I think sunspot 1026 was, but it doesn't appear as a sunspot to any of the observatories that track them. This can be puzzling, because if I look at a spot that bright via the STEREO animation that appears to the left, beyond the eastern limb past -90 degrees, I might assume that is a sunspot coming our way.

Perhaps someone is expecting a reappearance of either 1026 or 1027, because if we look at the October 1 forecast from the US Air Force and NOAA, it shows an expectation of a rising solar flux above 70 beginning October 17. It looks like a spot isn't expected any time soon, as they have the predicted solar flux for Friday (today) and Saturday, October 2-3 at 70, then down to 69 for October 4-8, 68 on October 9-14, then rising back to 70, then 72 for October 17-28. This forecast is likely to change, and is updated daily. The same forecast projects very quiet geomagnetic conditions, with a planetary A index of 5 off into the indefinite future. The sunspot number on Thursday, October 1 was 11, same as Wednesday, and today's is likely to be 0.

The three-month moving average of sunspot numbers that now includes data from September is the same as last month's three month average, which was calculated from sunspot numbers for June-August. It seems that both June and September had identical average sunspot numbers, so for the latest reading, the June data was dropped, the September data added, and the same 3-month average of 4.0 is the result.

Sunspot numbers for September 24-30 were 32, 25, 14, 11, 11, 14 and 11 with a mean of 16.9. The 10.7 cm flux was 74.6, 72.4, 71.8, 72.3, 73.2, 72.3 and 72 with a mean of 72.7. The estimated planetary A indices were 1, 2, 3, 8, 8, 2 and 4 with a mean of 4. The estimated mid-latitude A indices were 1, 1, 3, 8, 6, 0 and 5 with a mean of 3.4. The monthly averages of daily sunspot numbers for January-September were 2.81, 2.54, 0.77, 1.27, 3.97, 6.6, 5.07, 0.39 and 6.6. Our three-month moving average always is labeled with the middle month, so with the September data, we now have the August average, which is for July, August and September. For October 2008-August 2009, the moving average is 4.52, 4.39, 3.62, 2.19, 2.02, 1.49, 2.01, 4.23, 5.2, 4 and 4.

Dan Prebenda, K9DP, of Richmond, Indiana -- back on the air after 10 years QRT -- is frustrated trying to work fairly short skip on 30 and 40 meters CW around noon to 3 PM local time (1600-1900 UTC when local time is Eastern Daylight Time, which ends November 1 this year). He is experiencing a lot of fading, and the stations he is trying to work are about 300 to 700 miles away, mostly to the east and south of him.

Dan wonders if 30 meters will get better for this path with higher sunspot counts. I suggested he test some paths and seasonal variation using W6ELprop, a free program. Using either 0 or a smoothed sunspot number of 10, it looks like 40 meters is the best band, although 30 meters looks good 700 miles out to the southwest. I used 39.826 degrees north latitude, 84.896 degrees west longitude for Dan's location, based on the address in his FCC licensing record.

Philadelphia is about 500 miles almost directly east of him. At that distance, 30 meters doesn't look good until the smoothed sunspot number gets above 50, which is not where we are in the cycle. Same thing with Atlanta, at about 400 miles almost due south. But Dallas -- at about 800 miles and 237 degrees -- looks a lot better, with strong signals on 30 meters, 1400-2300 UTC (10 AM to 7 PM EDT) and a smoothed sunspot number of 2.

But 40 meters looks great for any of those paths, even with no sunspots, and he can test some assumptions using W6ELprop. He can look at any path on different dates, too, and should see seasonal variations. Instead of solar flux, use sunspot number with W6ELprop. If the program isn't set for sunspot number in the options, just precede the number by the letter "S." The program is designed to give a rough forecast using the predicted smoothed sunspot number for the month. It was 9 for September, and 10 for October. The most recent prediction is in PRF1774 here on page 8; there may be a new prediction next week in PRF1779. In the past couple of weeks, when we have actually had sunspots, I would average the three latest known sunspot numbers (a day's number is not available until the evening) from here.

The smoothed number changes for any month because it is based on actual sunspot numbers for the previous six months, and predicted sunspot numbers for about six months into the future. So the only smoothed sunspot numbers that we know for sure are at least six months old because they are all based on real sunspot data, with nothing predicted. To use current numbers, on September 26 during the day, the three latest known sunspot numbers were 31, 32 and 25, which averages to about 29.3. You can get the latest mid-latitude K index from WWV off the air, here or by calling (303) 497-3235. It is updated every three hours.

Meyersdale, Pennsylvania is about 300 miles due east of Dan, and for that short skip, 80 meters is the only realistic option, except for a dead period, 0230-1100 UTC. Forty meters is possible from 1600-1800 UTC, but the odds are against it on most days (this time of year). It looks better in the spring, 1600-2200 UTC, and a lot better when we get some sunspots.

Von Weddige, W5COW, of Hope, New Mexico (how did I guess his was a vanity callsign?), reported a surprising 6 meter opening on September 22. He made 19 contacts on SSB in 31 minutes, from 0022-0053 UTC. Von is in gridsquare DM72, and he worked stations in EM53, EM54, EM57, EM63, EM68, EM73, EM75, EM79, EM81, EM86, EM89, EN50, EN70 and EN71.

In last week's bulletin, Ken Tata, K1KT, talked about interesting conditions on 2 meters from his location in Rhode Island during a weeknight VHF sprint. Leo Halverson, WA2AMW, commented in response: "These conditions aren't all that rare at this time of year, although I usually encountered them later at night. They often go undetected because most of these openings happen during work-nights, when most people are asleep. I worked the second shift for many years and encountered these conditions during the homeward-bound commute.

"I found that they were most common, of greater duration, and with longer-distance propagation during the first two weeks of October. I also noticed that they were much more likely to occur on nights when a (mostly low) ground fog had risen and was very wide spread and thick, but very clear above. It also seemed that the sky was very clear and with good visibility of stars and distant high-altitude aircraft. The stars even seemed to have an extra twinkle to them. One night we had a roundtable going on one of the shore town repeaters, with stations from Nova Scotia to Kitty Hawk, North Carolina. One guy was on a handheld transceiver in his garage in Virginia Beach. I could copy all the stations on the input frequency on my mobile dual-band. The opening started fading out about 0330 EST. I never did find out why the ground fog was so indicative of these openings. I'm glad to be working the day shift, but I sure do miss those autumn midnight commutes."

Ken responded: "I don't have decades-long experience with fall tropo conditions, but Leo described the conditions to a 'T!' It was virtually dead calm. I also noticed the sky overhead was unusually clear. The stars did not twinkle and seemed a bit brighter than usual, perhaps because convection currents were minimal. We do get occasional ground fog here at this time of year but I didn't see any. As it cooled on my hilltop that evening, the formerly clear conditions gave way to a soaking fog at about 9:30. I was about 8 miles north of the beach and 2 miles west of Narragansett Bay. I think ground fog is not just an indicator. It's a medium with higher mass than the clear air above. It slows the lower part of the wavefront relative to the clear air above, tending to bend the wave along the surface of the Earth. Leo's observation of a '(mostly low) ground fog had risen' seems right on. As far as being not all that rare, well, I'll pay closer attention from now on! It was still a fun contest! And while I have experienced more extensive tropo propagation than that, I don't think I've ever heard so much widespread activity on 2 meters."

Tim Hickman, N3JON, confirmed that his long-path contact with VK4MA, mentioned in last week's bulletin, was in fact on 20 meters.

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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