Propagation de K7RA

There were no zero-sunspot days over the past week.
In fact, the average daily sunspot number was a little more than double the previous week's numbers, rising over 17 points to 33.4. This was a nice little up-tick toward the solar cycle minimum, coming with the start of spring for the Northern Hemisphere.

Unfortunately for HF operators, the average geomagnetic numbers doubled as well. This and the associated aurora were triggered by a solar wind stream that hit Earth beginning on Saturday, March 18. Maximal effects were felt the following day, when the College A index, (measured less than two degrees latitude south of the Arctic Circle), rose to 51 on Sunday.

Saturday's College A index was 39, but on Friday, March 17 it was only 2, a very quiet number. The Planetary A index over those same days was 3, 26 and 37, and the mid-latitude A index was 2, 15 and 24.

This weekend is the CQ World Wide WPX SSB Contest, and there shouldn't be any nasty surprises regarding propagation. The predicted planetary A index for the next five days, March 24-28 is 12, 12, 10, 7 and 5.

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 and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page at,
http://www.arrl.org/tis/info/propagation.html. An archive of past propagation bulletins is found at, http://www.arrl.org/w1aw/prop/.

Sunspot numbers for March 16 through 22 were 22, 24, 27, 40, 33, 39 and 49 with a mean of 33.4. 10.7 cm flux was 72.4, 72, 72.4, 75.2, 76.9, 76.7, and 75.9, with a mean of 74.5. Estimated planetary A indices were 6, 3, 26, 37, 22, 13 and 10 with a mean of 16.7. Estimated mid-latitude A indices were 4, 2, 15, 24, 14, 8 and 9, with a mean of 10.9.

Tad Cook, K7RA

Source: The American Radio Relay League

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