The K7RA Solar Update


Again this week, we saw a new, but brief sunspot, sunspot 993. Judging from the polarity of the spot, it looks to be from new Solar Cycle 24; this spot was south of the solar equator, so it has the same polarity as any Cycle 23 spot that was north of the equator. After two days it was gone, not from drifting over the edge of the visible solar disk -- it just disappeared.

Geomagnetic indices were mostly quiet this week, except for some only slightly unsettled planetary A index numbers for May 2-3. The next active geomagnetic period is expected May 20, with a planetary A index of 25. For May 9-15, the predicted planetary A index is 8, 5, 5, 5, 12, 8 and 5. Sunspot numbers for May 1-7 were 0, 0, 0, 13, 15, 0 and 0 with a mean of 4. The 10.7 cm flux was 68.5, 68.1, 67.3, 68.3, 67.6, 67.2 and 66.5 with a mean of 67.6. Estimated planetary A indices were 9, 12, 12, 8, 11, 10 and 4 with a mean of 9.4. Estimated mid-latitude A indices were 6, 7, 9, 6, 8, 9 and 5, with a mean of 7.1. For May 9-15, Geophysical Institute Prague predicts quiet conditions May 9, quiet to unsettled May 10, unsettled May 11-13, quiet to unsettled May 14 and quiet again on May 15.

An e-mail from Martin McCormick, WB5AGZ, of Stillwater, Oklahoma, mentioned sporadic-E propagation and meteor showers. Last Saturday, May 3, he tuned to Channel 2 -- a television frequency centered on 55.25 MHz -- with his receiver set to CW mode, upper sideband. He said that the closest Channel 2 station is 50 miles from him in Tulsa, so that makes spotting on this frequency possible, because locally from his position it is quiet. He quickly heard a ping, then another, then a very loud ping with the slide-whistle effect associated with Doppler shift. This was from the eta Aquarids meteor shower, which peaked two days later on May 5. The eta Aquarids occur when earth passes through dust left behind from Halley's Comet.

Martin noted that on February 17, 2009, when analog television goes dark, we will lose a large group of powerful beacon stations for the low VHF spectrum that is useful for detecting 6 meter openings. There are about 50 active broadcasters on Channel 2 in the US, I assume most operating around the clock. So for the Sporadic-E seasons, we only have this summer remaining to use this tool, plus the shorter Sporadic-E winter season. After that, it's all quiet. I don't know what will eventually replace television broadcasting in the spectrum just above our 6 meter band when television channels are refarmed.

Last week's bulletin mentioned locations of magnetometers such as the Boulder and Fredericksburg monitoring stations that are used to generate separate mid-latitude K and A indices. I've wondered if these same geomagnetic indicators were generated for other stations, such as the one at Newport, Washington, close to the Idaho border.

Steve Lybarger, NU7T of Sparks, Nevada sent a link showing seven hourly K index readings from nine magnetometers, most in North America. The locations of most stations were shown in last week's bulletin; for Meanook, Ottawa and St Johns, check here for National Resources Canada information. For Hartland, which is in southwest England, check here. Note that first link, does not only show a new K index every hour, but an hourly planetary A index based on the planetary K index for the past 3 and 24 hours, updated every hour.

Each of the three countries has a slightly different method of showing location coordinates. The United Kingdom uses the standard system that most of us are accustomed to, rather than the rather arcane scheme outlined last week for USGS sites; the Canadian method seems to combine both, using standard figures for latitude, but longitude extending to 360 degrees. So for locating Canadian magnetometers, use their stated latitude under geographic coordinates, but subtract their stated longitude from 360 to obtain west longitude.

When comparing geomagnetic data, we are mostly interested in latitude, because during active geomagnetic periods the activity is more intense at higher latitudes.

Note that from the Canadian site, you can drill down to get the 3-hour geomagnetic K index for Ottawa, Victoria and Meanook.

Last week's bulletin promised to go over some simple methods for finding the best times and frequencies that are likely to produce good propagation from your location to any other. This uses the free program, W6Elprop. You can find past bulletins which outline uses for the program here.

W6Elprop uses predicted smoothed sunspot numbers to show the user propagation paths that are most likely. I have been advised that these sorts of programs do not produce better results by using today's actual solar flux or sunspot number. Rather, it calculates the Maximum Usable Frequency (MUF) based on predicted smoothed sunspot number, designed so that about half the time the actual MUF is above the predicted MUF, and half the time below. Remember that MUF is calculated for a specific path between two specific points on the globe at a particular time and season (based on date).

You can usually find the current predicted smoothed sunspot number updated monthly in the Preliminary Report and Forecast from the Space Weather Prediction Center. For instance, on page 9 of this week's issue shows the May 2008 predicted smoothed sunspot number as either 5 or 6, based on a lack of consensus among panel members who predict the next Solar Cycle. So use either number, or 5.5 if you wish.

If you want to use a sunspot number that more closely reflects recent activity, you can average the latest three sunspot number readings. For today, I would use a sunspot number of zero. If it was May 6, and the table only showed data through May 5, I would use an average of 9.3. You can set up W6Elprop to default to either solar flux or sunspot number entries. If you want to change at any time, or insure your intended figures are used, precede the number with the letter S for sunspot number, or F for flux.

You can also change or add frequencies to the predictions, for 12, 17 and 30 meters, shortwave listening or the relatively new 60 meter band. Users can add atlas info to add target locations. You end up with some possible signal levels and ratings for each half hour. The A designator means the path is likely to be available close to 100 percent of the time, and of course, higher signal levels are good. If you want to add the latest K index, you can get it from NOAA.

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.