The K7RA Solar Update
As mentioned in last week's report, Carl Luetzelschwab, K9LA, is filling in for your regular reporter Tad Cook, K7RA. For the reporting period August 1-7, solar activity was at very low levels and the geomagnetic field was at quiet levels. Solar activity is expected to continue to be very low for the next several days. As for geomagnetic field activity, the Australian Space Forecast Centre issued a geomagnetic disturbance warning on August 6 for quiet to unsettled, and then unsettled to active conditions (with possible minor storm periods) on August 8 and August 9, respectively.
Sunspot numbers for July 31-August 6 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 65.5, 66.1, 66.2, 65.5, 66.2, 66.5 and 67 with a mean of 66.1. Estimated planetary A indices were 4, 3, 3, 4, 4, 3 and 4 with a mean of 3.6. Estimated mid-latitude A indices were 4, 2, 2, 3, 3, 3 and 5 with a mean of 3.1.
Other than a new-cycle magnetic dipole on August 3 that didn't turn into a sunspot region, the Sun was again blank for the entire reporting period. Kind of sounds like a recording, doesn't it? A good summary is:
Here we sit at solar min
Wondering when Cycle 24 will begin
It seems like we've been at solar minimum forever. In fact, there have been several news releases hinting that this solar minimum period between Solar Cycle 23 and 24 is unusual.
The analysis of recent spotless days compared to historical spotless days led NASA solar physicist Dr David Hathaway to conclude that nothing is unusual about this solar minimum period. Another way to view solar minimum is to look at the duration when the smoothed sunspot number is below 20. Historically, this duration has ranged from a short 17 months to a long 96 months, with an average of 37 months. Solar Cycle 23 descended below 20 in February 2006, and Cycle 24 is predicted to ascend above 20 in early 2009. That's around 36 months, so everything appears to be pretty normal so far and agrees with Dr Hathaway's conclusion. We'll just have to be patient until Cycle 24 starts ramping up. The good news is that we have seen three sunspot regions tied to Cycle 24 (January 4, April 13 and May 5), so it's coming.
What can you do around solar minimum? One activity would be to get on the low bands for the fall/winter season -- the low bands should be very good. Another activity would be to take advantage of summer sporadic-E (and in December, too, but it's not as prevalent). For example, last weekend provided some excellent 6 meter propagation. And participants (your author included) in the CW running of the North American QSO Party (sponsored by NCJ) enjoyed 10 15 meter sporadic-E openings; this likely happens a lot more than we think -- a dead band may not be dead, just unoccupied. And since mid-latitude sporadic-E is not tied to sunspots, we can have fun throughout an entire solar cycle.
Speaking of sporadic-E, last week's Update reported Dave Greer, N4KZ, of Frankfort, Kentucky, working EA8/DL6FAW on 6 meters on both CW and SSB. This brought a reply from Norbert Scherer, DL6FAW. Norbert reports that he's been operating on 2 meters for many years, but his 6 meter activity is relatively new. Since 2006, he has been running 100 W to a simple 5-element Yagi when in Spain.
Norbert continues: "In the first weeks I only heard North America in the middle of the day. I never expected any opening after midnight local time. But by carefully monitoring the beacons, I was surprised to hear, for example, WZ8D/B late in the evening. Sometimes I started to call CQ and there was no reply at all. The following day, when I heard the beacon again and nothing else, there were 10 people calling at the same time. Tim, KY5R, told me last week that I was the only signal on the band he could hear. I hope there will be more good propagation to North America in the coming weeks, although the sunspot number is 0! I checked out some Web sites listing solar activity, sunspot number, K-index, solar winds and such for July 2008, but I couldn't find any correlation between the data provided there and my log."
Norbert's attempt to correlate 6 meter E-skip to sunspots came out as expected -- as stated earlier, there doesn't appear to be any tie between where we are in a sunspot cycle and the occurrence of mid latitude sporadic-E.
Finally, in last week's Update, Jim Henderson, KF7E, of Queen Creek, Arizona, provided some good observations and comments about the day-to-day variability of the ionosphere. A good supporting example of his observations is the F2 region MUF over the Millstone Hill ionosonde (in Massachusetts), assuming it's the mid-point of a 3000 km hop.
In July, when the solar flux was for all intents and purposes constant, the 3000 km MUF varied from a low of 8.9 MHz to a high of 19.6 MHz. Jim's comments, along with the Millstone Hill data, are in agreement with ionospheric studies showing that although solar radiation is the instigator of the ionization process, two other factors appear to be more significant in determining what the F2 region ionosphere is doing right now: geomagnetic field activity and events in the lower atmosphere coupling up to the ionosphere.
What does all that mean? It simply means plugging the daily solar flux into your favorite propagation prediction program really doesn't tell you what the ionosphere is doing today. This day-to-day variability is the reason our prediction programs were designed to be statistical over a month's time frame. We do not have daily predictions and the developers never intended that they be daily predictions, as they were aware of the unpredictability of the day-to-day variation of the ionosphere. Perhaps some day we'll figure all this out, but for now the best way to tell if one of the higher bands is open is to listen to the NCDXF/IARU beacons).
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.