Propagation de K7RA

We just saw more 0-sunspot days, followed by the brief emergence of small spots, then more days with no sunspots. The average daily sunspot number for the past week was down nearly 70% from the previous week, to 5.9.

A solar wind hit earth on Tuesday, March 13, and a rise in
geomagnetic indices was the result, with the planetary A index rising to 26. The A index measured at Fairbanks, Alaska, the college A index, rose to 50. The next period of higher geomagnetic activity is predicted for March 27, then April 9 and April 23.

Last week's note about 11 being the smallest sunspot number greater than 0 brought several puzzled responses, including one from Darrell Bellerive, VA7TO of Grand Forks, British Columbia, who wondered if there were other gaps in the range of possible sunspot numbers.

Barry Pfeil, K6RM of Mountain View, California wrote, "I thought the sunspot number was LITERALLY the number of sunspots and could be anything from 1 on up."

One might think so, but the number is actually somewhat subjective, and factors in the number of groups of sunspots. The National Geophysical Data Center has a link at,
http://www.ngdc.noaa.gov/stp/SOLAR/SSN/ssn.html which explains the method. The number of groups of spots is counted, and that number is multiplied by 10, then added to the number of individual sunspots. So if you saw 7 sunspots in 4 groups, the sunspot number would be 47.
One spot would be 11, two spots in one group would be 12, etc. By subjective, I mean that someone must look at the spots, decide what constitutes a group, and count them.

Note that the Vernal Equinox is coming up in a few days. At 0007z on March 21 (which is Tuesday, March 20 in North America) the sunlight hitting the northern and southern hemispheres will be equal. All over the world, the sun will rise in the morning, and then set 12 hours later. Sunrise in Seattle at 47.67 degrees north latitude will be 1416z, sunset at 0216z. In Matto-Grosso Brazil at 15 degrees south latitude, sunrise at 0943z, sunset at 2143z. In England at
52.2 degrees north latitude, 1 degree west longitude, sunrise at 0611z, sunset at 1811z. With an equal measure of sunlight striking both hemispheres, the equinox is a good time for HF propagation, with the possible exception that we have very low sunspot activity.

A correction from last week: Dave Green, VE3TLY was wrongly identified as VE5TLY.

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 March 8 through 14 were 0, 0, 16, 14, 11, 0 and 0 with a mean of 5.9. 10.7 cm flux was 72.5, 71.6, 71.2, 71, 71.2, 71.4, and 70, with a mean of 71.3. Estimated planetary A indices were 4, 2, 4, 8, 9, 26 and 8 with a mean of 8.7. Estimated mid-latitude A indices were 3, 1, 2, 6, 7, 18 and 9, with a mean of 6.6.

Source: The American Radio Relay League

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