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 Previous: Surfin': It's Only Software |  Next: FCC Designates Hearings on Three Amateur Radio Applications |
SEATTLE, WA, May 25, 2007 -- This week saw a return to active geomagnetic conditions after a period of relative quiet. The planetary A index reached a high of 42 on Wednesday, May 23, and the mid-latitude A index that day was 28. At the same time, sunspot numbers are dropping -- from a high of 56 on May 16 to 44, 23, 15, 14, 12 and 0 on May 19-24. Currently the interplanetary magnetic field points south, making Earth susceptible to geomagnetic upsets from solar wind.
We could see a blank sun through the end of May. On Thursday, May 24 at 2134 UTC the US Air Force and NOAA released a second daily 45-day outlook, revised from the initial forecast 35 minutes earlier, calling for solar flux values through the end of the month of 70, 70, 65, 65, 65, 70 and 70 for May 25-31. When the sun is devoid of spots for extended periods, we often see solar flux values below 70, so predicting a solar flux of 65 implies no sunspots.
The three lowest solar flux values I'm aware of were between July 19-22, 1996, when they were 64.9, 66.1, 65.4 and 65.1. There you have it: The lowest, second lowest and third lowest solar flux values all during those four days. The fourth lowest value I'm aware of was 65.8 the year before, on May 27, 1995. During the current sunspot minimum and the previous one around 1996, I am not aware of any other solar flux values below 66, but my records only go back to January 1, 1989. My records of solar flux resolved to one-tenth of a point don't begin until May 27, 1992. Prior to that, they are all recorded as whole numbers.
Geomagnetic indices should remain active for the next few days, with predicted planetary A index for May 25-29 at 25, 25, 20, 10 and 5. Geophysical Institute Prague predicts active conditions for May 25-26, unsettled May 27, quiet to unsettled May 28, and quiet May 29-31. During the CQ World Wide WPX CW Contest this weekend, expect no sunspots and declining but still active or unsettled geomagnetic conditions.
Several readers this week reported recent 6-meter openings. Mark Bell, K3MSB, of Airville, Pennsylvania, (about 40 miles southeast of Harrisburg in grid square FM19) worked NP4A (FK68) and WP4N (FK78) on May 13 around 0000 UTC. Don't miss Mark's photos of old classic ham radio gear.
Mike Williams, W4DL, of Pompano Beach, Florida, sent a message from Dayton Hamvention about an opening on 6 meters on May 14.
"After work, I dutifully turned on the 6 meter gear and by 8 PM that evening, I had worked a page full of stateside stations on CW, (my favorite), SSB, FM and AM. What a pleasant early evening! There is much more activity on 52.525 and above and numerous CW stations as compared to last year."
Kenneth Tata, K1KT, of Warwick, Rhode Island, (FN41) wrote on May 22 that a strong 6 meter opening began at 2030 UTC toward the southeastern United States. A few days earlier, he sent his favorite links for spotting VHF openings. For 2 meters, there is a map based on APRS networks. Also see a description of the network.
Ken also likes these tropo ducting maps. He checks the 2 and 6 meter loggings at DXWorld.com. Ken says the VHF DX site is "much more ambitious."
"Gabriel has done a truly amazing job with this site! He collects VHF/UHF contacts BY BAND and presents them on a map TO USER SPECIFICATIONS!! It can also automatically email propagation warnings to subscribers! And there's a lot more there, too."
Ralph Burgess, VE3BSJ, asks: "Very simply, what figures should I hope for? Right now, I see on the top of my DX monitor: SF=70 A=37 K =3. What would show an improvement for me?"
Here's what I told him:
An A index of 37 is generally undesirable, although K of 3 means conditions have settled down a bit. The exception is if you want to use auroral propagation on 6 meters, in which case a higher number is desirable. Aurora appears at lower and lower latitudes as the A and K index rise.
We want the solar flux (70) to be as high as possible. It generally tracks with sunspot numbers. Minimum solar flux is below 70, when there are no sunspots. For good HF conditions, we want many sunspots with less geomagnetic activity.
Here is the relationship between A and K index. The A index is calculated every 24 hours and is based on the 8 K index readings done every 3 hours throughout the day.
From the nomograph at the URL above we can see that if we had 24 hours of K=1, A would be 4, A would be 7 if all the previous K index readings were 2, 15 if they were 3, and 27 if they were 4. So your A index of 37 probably means that most of the day's K index readings were around 4 or 5.
The latitude of your address in Parry Sound is 45.344 degrees north, which is actually 2.3 degrees south of my latitude in Seattle. The farther north we are, the more we are negatively affected by high A and K index. In fact, these geomagnetic indices can be measured anywhere, and when there is geomagnetic activity you will see higher numbers at higher latitudes.
See the Daily Geomagnetic Data from NOAA's Space Environment Center. The A index you are seeing may be from Boulder, Colorado, and is the number derived at the end of the day (in UTC) for yesterday, while the K index is the most recent reading: Or perhaps it is from some European source.
My general rule is that HF conditions are better when the K index is below 3, and worse when they are above 3. We have seen very quiet conditions most recently, but when we have more sunspots in a few years a Boulder A index of 3 will be about average.
You can see from that table of A and K index that the College (Fairbanks, Alaska, at 64.9 deg N) index (both K and A) yesterday (May 23) was much higher than the mid-latitude index, which is from Fredericksburg, Virginia, at 38.3 deg N latitude. The planetary indices are derived from a combination of magnetometers around the world. The Boulder numbers on WWV are from 40 degrees north latitude.
For More Information
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page and the article "The Sun, the Earth, the Ionosphere: What the Numbers Mean, and Propagation Predictions," by Carl Luetzelschwab, K9LA. An archive of past bulletins is on the ARRL Web site. The propagation charts that formerly appeared in QST now are available on the QST Propagation Charts page on the ARRL Web site.
Weekly Sunspot Numbers
Sunspot numbers for May 17 through 23 were 30, 45, 44, 23, 15, 14 and 12, with a mean of 26.1. The 10.7 cm flux was 76.5, 75.8, 74.8, 74.1, 73.2, 72, and 70.1, with a mean of 73.8. Estimated planetary A indices were 6, 18, 12, 6, 6, 11 and 42, with a mean of 14.4. Estimated mid-latitude A indices were 4, 15, 10, 6, 6, 10 and 28, with a mean of 11.3.
Amateur solar observer Tad Cook, K7RA, 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. Readers may contact the author via e-mail.
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