Propagation de K7RA

Solar activity remains low, and was lower this week than the week before. Average daily sunspot numbers dropped over six points to 19.4, and solar flux was down over five points to 70.7.

July 13 saw the solar flux dip just barely below 70 to 69.9. During extended periods with zero sunspots, we will see solar flux around 67 or 68. I believe the solar flux hasn't been below 70 in almost exactly nine years, back to July 17, 1997 when it was also 69.9.

Today the sun appears spotless, although the sunspot number is above zero. Expect continued low levels of solar activity. For the next few days expect solar flux around 70, rising to 75 after Sunday, July 23. This is not a big change. It is roughly equivalent to the sunspot number rising from 11 to 18. This doesn't mean that solar flux and sunspot numbers are completely independent. This week we saw average solar flux around 71 and average sunspot number around 19.
Five years ago with an average solar flux around 141, average daily sunspot numbers were around 162.

Geomagnetic indices should be quiet, with a planetary A index of five. The next period of higher geomagnetic activity due to recurring coronal holes rotating into view is some moderate activity expected around Tuesday, July 25, and then some higher activity centered on August 1. This is a prediction from the U.S. Air Force Space Weather Operations. Geophysical Institute Prague predicts quiet conditions for July 21-24, unsettled conditions July 25-26, and quiet to unsettled July 27.

Check this article on Space Weather from The Industrial Physicist:
http://www.aip.org/tip/INPHFA/vol-9/iss-6/p18.html. Note the nice illustration of magnetic and solar convection patterns about half way down the page.

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/ .

Sunspot numbers for July 13 through 19 were 11, 15, 17, 20, 23, 26 and 24 with a mean of 19.4. 10.7 cm flux was 69.9, 70.9, 70.2, 70.8, 71, 71.2, and 71.1, with a mean of 70.7.

Estimated planetary A indices were 5, 14, 6, 4, 4, 3 and 2 with a mean of 5.4. Estimated mid-latitude A indices were 3, 10, 5, 2, 2, 2 and 2, with a mean of 3.7.

Source: The American Radio Relay League

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