The K7RA Solar Update

SEATTLE, WA, Jul 21, 2006--Solar activity remains low, and was lower this week than the week before. Average daily sunspot numbers dropped by more than 6 points to 19.4, and solar flux was down by more than 5 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.

The Industrial Physicist has an interesting article, "Understanding and predicting space weather," by Dawn Lenz, on its Web site. Note the illustration of magnetic and solar convection patterns about halfway down the page.

For More Information

For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page and the article "The Sun, the Earth, the Ionosphere: What the Numbers Mean, and Propagation Predictions," by Carl Luetzelschwab, K9LA. An archive of past bulletins is on the ARRL Web site.

Weekly Sunspot Numbers

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.

Amateur solar observer Tad Cook, K7RA, 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. Readers may contact the author via e-mail.

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