Propagation de K7RA

28 July, 2007

Average daily sunspot numbers and solar flux are down this week. Average daily sunspot number declined nearly 28 points to 1.7, and the daily solar flux average was down nearly 7 points to 67.4.

When the solar flux is less than 70, it often means no sunspots, and the sunspot number has been zero for a week. Predicted solar flux for the next week is 70, which suggests a sunspot or two, with the chance for sunspots increasing after August 2.

Currently the IMF (Interplanetary Magnetic Field) points south, making our planet vulnerable to geomagnetic upset. The effect from solar wind should be mild, with the planetary A index for July 27-31 predicted at 15, 5, 5, 8 and 15. Geophysical Institute Prague predicts quiet to unsettled conditions for July 27, quiet for July 28, quiet to unsettled July 29, unsettled July 30, quiet to unsettled July 31 and quiet again on August 1-2.

In response to our links to historical sunspot activity graphs at wm7d.net, Sid Sosin, W7SID of Bellevue, Washington commented, ''What data was available on sunspot activity in 1761 and the remainder of the 18th century, and the 19th century, for that matter?''

Galileo was an early observer and recorder of sunspots, and you can see his wonderful daily sketches from the 18th century at http://hsci.cas.ou.edu/exhibits/exhibit.php?
exbgrp=1&exbid=13&exbpg=2
. You can even watch animated versions of his drawings, showing the daily progression of sunspots across the sun's earth side face at the above-mentioned link, and at
http://galileo.rice.edu/sci/observations/
sunspot_drawings.html.

Jim Henderson, KF7E of Queen Creek, Arizona asked what the lowest recorded solar flux is. We went over that a couple of months ago in ARLP022, and the lowest value I've seen is right around 65.

Robert Wood, W5AJ of Midland, Texas sent a link to a picture of the sun and asked about a dark patch near the northern pole. I don't know what it is, but I assume it might be a cooler area, because sunspots are dark and they are cooler relative to nearby areas. It sure is a nice picture though. See it at http://umbra.nascom.nasa.gov/eit/images/
latest_eit_304_full.gif.

Don Josephs, K5DEJ of Fredericksburg, Texas wrote to ask about the relationship between solar flux, sunspot numbers and the A index, and what they mean to propagation.

You can see from this table at
http://www.sec.noaa.gov/ftpdir/indices/DSD.txt that solar flux tends to rise and fall with sunspot number. The flux is 10.7 cm wavelength (about 2.8 GHz) energy measured at a Canadian observatory in British Columbia. One advantage of measuring solar flux is that the measurements are objective, while the sunspot number is somewhat subjective. But for our purposes, if we want to predict radio signals on a certain day over a certain path, an average of recent sunspot numbers is a better value to use than solar flux.

The A index is derived from eight daily readings from magnetometers. We generally want to see those numbers low, especially if we are trying to propagate radio signals over polar paths, because higher geomagnetic activity signals greater absorption. But watch over the next few years as solar activity increases. Greater solar activity not only may signal more sunspots, but it also means more solar
flares and solar wind, which often affects earth's Geomagnetic field. So increased sunspot activity is a kind of double-edged sword. We want more sunspots, but along with that can come greater chances of geomagnetic storms.

A good way to visualize the effects of sunspot activity over a
particular path is to use a couple of free computer programs,
W6Elprop and VOAprop. W6Elprop will give you likely signal levels over a path between two locations, while VOAprop is great for visualizing how signal coverage shifts through the day. This link will take you to past bulletins which discuss these programs, and recommend ways to use them: http://tinyurl.com/2d8w87.

If you would like to make a comment or have a tip for our readers, email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL Technical Information Service at
http://www.arrl.org/tis/info/propagation.html.

For a detailed explanation of the numbers used in this bulletin, see http://www.arrl.org/tis/info/k9la-prop.html.

An archive of past propagation bulletins is at http://www.arrl.org/w1aw/prop/ .

Monthly propagation charts between four USA regions and twelve overseas locations are at http://www.arrl.org/qst/propcharts/.

Sunspot numbers for July 19 through 25 were 12, 0, 0, 0, 0, 0 and 0 with a mean of 1.7. 10.7 cm flux was 68.3, 67.3, 66.4, 66.2, 67.2, 68, and 68.6, with a mean of 67.4. Estimated planetary A indices were 3, 12, 12, 4, 3, 2 and 2 with a mean of 5.4. Estimated mid-latitude A indices were 3, 9, 10, 3, 4, 2 and 2, with a mean of 4.7.

Source: The American Radio Relay League

• All propagation reports can be found at:
http://www.southgatearc.org/propagation