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The K7RA Solar Update


The past few days have had very stable geomagnetic conditions. After unsettled to active geomagnetic indicators on March 26-28, conditions quieted down dramatically. Combined with the nearly two-week run of sunspots and the spring season, this makes good HF conditions. There were actually three sunspots, beginning on March 23 with the first one and a sunspot number of 14. March 24 and 25 each brought one new spot; the sunspot number rose to 35 and 52 on those days. Activity peaked between March 26-29 with daily sunspot numbers of 63, 57, 63 and 50. Yesterday, April 3, the sunspot number was back to 14 again, as one-by-one, the three spots drifted from view. Today's sunspot number may be back to zero, and it may stay that way until April 18-20. Sunspot numbers for March 27 through April 2 were 57, 63, 50, 41, 45, 25 and 24 with a mean of 43.6. The 10.7 cm flux was 84.8, 82.9, 82.6, 80.5, 79.2, 77.8 and 75.9 with a mean of 80.5. Estimated planetary A indices were 31, 21, 8, 8, 4, 4 and 1 with a mean of 11. Estimated mid-latitude A indices were 19, 13, 6, 6, 2, 5 and 1, with a mean of 7.4.

Conditions were remarkably quiet on April 2-3 with many periods having a K index of zero, no matter the latitude. April 2 near Fairbanks, Alaska, the College K index as measured by the local magnetometer was zero during all eight three-hour periods. Of course, this resulted in an A index for the day of zero. You can go here to see the K index and A index for the past 30 days, as measured at Fredericksburg, Virginia and Fairbanks, Alaska, as well as the Planetary index, derived from a number of predominately higher latitude magnetometers. With eight K index measurements per day, times three indexes, times 30 days, you will see more than 700 readings.

This weekend, April 5-6, will probably see the return of solar wind and associated geomagnetic activity. Predicted Planetary A index for April 4-13 is 10, 15, 15, 12, 12, 12, 12, 10, 5 and 5. Geophysical Institute Prague predicts quiet to unsettled conditions for April 4, active conditions for April 5, unsettled to active April 6, unsettled April 7, unsettled to active April 8 and unsettled April 9-10.

Because we now have all sunspot numbers for March, we can take another look at our three-month moving average to try to spot the sunspot minimum. The latest number, 8.4 for February 2008, is the average for all the daily sunspot numbers from January, February and March. We simply add up all the daily sunspot numbers (the sum is 763) and divide by the number of days (91) to get an average of 8.3846 that we approximate as 8.4. It still looks as if the sunspot minimum must have occurred in October 2007.

May 06 39.7

Jun 06 28.9

Jul 06 23.3

Aug 06 23.5

Sep 06 21.2

Oct 06 24.1

Nov 06 23.1

Dec 06 27.3

Jan 07 22.7

Feb 07 18.5

Mar 07 11.2

Apr 07 12.2

May 07 15.8

Jun 07 18.7

Jul 07 15.4

Aug 07 10.2

Sep 07 5.4

Oct 07 3

Nov 07 6.9

Dec 07 8.1

Jan 08 8.5

Feb 08 8.4

For a less-smoothed look, here are the monthly averages:

Apr 2007 6.9

May 2007 19.8

Jun 2007 20.7

Jul 2007 15.6

Aug 2007 9.9

Sep 2007 4.8

Oct 2007 1.3

Nov 2007 2.9

Dec 2007 16.3

Jan 2008 5.1

Feb 2008 3.9

Mar 2008 15.9

The monthly averages above still point to October 2007 as the sunspot minimum, but you can see the data is not as smoothed as the three-month averages.

Michael Best, WD4DUG, of Greensboro, North Carolina, sent a link to a NASA article about the recent three sunspots from the last solar cycle. Bill Balzerini, KL7BB, of Federal Way, Washington, sent the link about an ionospheric sounder in Alaska at the HAARP facility.

Amateur solar observer Tad Cook, K7RA, of 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. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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