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SEATTLE, WA, Sep 16, 2005--This week the sun has given us a tremendous amount of activity in the form of large solar flares. A geomagnetic storm is still in progress, and the planetary A index from Saturday through Thursday, September 10-15, was 30, 105, 66, 51, 25 and 43. These are high numbers.
The average planetary A index for this week more than doubled to 43.1. Average daily sunspot numbers more than quadrupled to 71.1. These numbers compare the seven days ending Wednesday, September 14 with the previous seven-day period.
Next week is the Northern Hemisphere's autumnal equinox. This period could be a good one for HF propagation, but only if solar flares quiet down and the sunspot count doesn't sink back toward zero. The sunspot number rose above 100 on Sunday, September 11, the first time it's done that since August 3.
The source of all this excitement is a single, large sunspot group, number 798. This spot was just peeking around the edge of the visible solar disk on September 9, but by September 14-15 it was aimed squarely at our planet. The last time around it was much smaller and still emerging. Although not aimed at Earth on September 7, that day it produced an X17 solar flare--the fourth largest detected over the past three decades. Over the next week it produced eight more flares, each causing HF radio blackouts.
Of course, VHF operators probably didn't mind all the disruption. You can check the 50 MHz Propagation Logger to see what they've been up to on 6, and The DX World Web site provides a further look back.
Steve Lyon, WB6RIB, and several others sent in an article from NASA about all this activity in the year before the solar cycle bottom, titled "Solar Minimum Explodes."
Over the next few days look for declining geomagnetic numbers, but fairly good sunspot and solar flux values. (Remember, HF operators generally want the sunspot and the somewhat-related solar flux numbers to remain high, with the geomagnetic A index and related K index as low as possible). Predicted solar flux for Friday through Monday, September 16-19 is 115, 110, 110 and 105. Predicted planetary A index for those same days is 25, 15, 10 and 10. Geophysical Institute Prague predicts active to minor storm conditions for September 16, active conditions on September 17 and 20, unsettled to active conditions September 21, unsettled conditions for September 18 and 22, and quiet to unsettled conditions on September 19.
Ed Douglass, AA9OZ, is trying for his second 5-Band DXCC award. The first time around was as 7P8DX in Lesotho from 1986-1992. This time he wants to do it from Sturgeon Bay, Wisconsin--just below the 45th parallel on a peninsula extending into Lake Michigan. He aims to work 100 countries on 75 and 80 meters during the sunspot minimum, and he asked if the absence of sunspots might improve his chances on lower frequencies.
Certainly the MUF (maximum usable frequency) is lower with fewer sunspots, so openings on 10-15-20 meters are much less common. But I seemed to recall Carl Luetzelschwab, K9LA, having something to say about the absence of solar activity producing better conditions overall on the low frequencies.
Carl referred me to an interesting article he wrote for the September/October 2005 issue of The DX Magazine titled "Getting Ready for Solar Minimum." Among other issues, the article discusses what happens with 160 and 80 meter propagation passing through the auroral zone. This includes West Coast North America-to-Europe, Midwest-to-Europe and Japan, and East Coast-to-Japan paths. During the solar minimum, there is less chance of ionospheric disturbance in northern latitudes.
Carl writes, "In general, a quiet high latitude ionosphere provides the best propagation on the lower bands for paths near or going through the auroral zone." Although this excellent article is not online, you can find similar material by entering a query for +K9LA + "auroral zone" in a search engine such as Google. One link returned was for our bulletin #8 from 2004, which talked about this same issue, and mentions that Carl wrote about this in the March 2004 issue of Worldradio. The Space Weather site has current conditions in the auroral zone north of North America.
Terry Oldham, KH6MT, wrote asking about 10 meters--an often difficult band at the bottom of the cycle. He lives in north-central Florida, between Jacksonville and Tampa, and wants to know when 10 might be open to El Paso, Texas. He mentioned that the window used to run from September through April, but last year he saw no window at all.
I told Terry about W6ELprop, the free propagation program for the PC, and mentioned he could plug in numbers for that path to see what pops up. I tried it, and over the approximately 1500 miles at this time of year, a sustained sunspot number a little higher than we've seen recently would help. Still, if you plug in the average sunspot number for the past week (71.1), according to this program propagation is quite possible. With about 10 more points, or perhaps going over to the 12-meter band, the odds look quite good.
For more information concerning radio propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page. An archive of past bulletins is on the ARRL Web site.
Sunspot numbers for September 8 through 14 were 36, 59, 59, 101, 62, 95 and 86, with a mean of 71.1. 10.7 cm flux was 94.1, 99, 116, 109.7, 118, 114, and 116.6, with a mean of 109.6. Estimated planetary A indices were 8, 17, 30, 105, 66, 51 and 25, with a mean of 43.1. Estimated mid-latitude A indices were 5, 12, 15, 53, 32, 26 and 13, with a mean of 22.3.
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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