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The K7RA Solar Update

10/17/2008

Finally, we are seeing Solar Cycle 24 sunspots that don't emerge on one day, only to evaporate the next. That's right -- sunspots, as in two or more. On Friday, October 10, sunspot 1005 emerged at high latitude over our Sun's eastern limb; that day's sunspot number was 12. On the following day, the sunspot number rose to 16 and a solar wind emerging from a coronal hole caused a geomagnetic storm. The planetary A index rose from a quiet 3 on Friday to 37, and the mid-latitude A index was 20. The 3-hour planetary K index reached a maximum of 7 that day, a high value for that scale. Conditions have quieted again since then.

On Sunday, Monday and Tuesday -- as the spot progressed toward the center-north of the solar disk -- sunspot numbers were 16, 15 and 14 as the dark spot began to fade. On Wednesday, the sunspot number faded another point to 13, but on Thursday, October 16, sunspot 1006 emerged, but this time in the southwest corner, about to rotate out of view. The sunspot number for Thursday jumped to 24.

On Wednesday of this week, a reading of activity on the side of the Sun facing away from Earth found another possible sunspot. This was detected using a method called helioseismic holography that depends on pressure waves bouncing around our Sun's interior. Take a look here and here for more detail.

Sunspot numbers for October 9-15 were 0, 12, 16, 16, 15, 14 and 13 with a mean of 12.3. The 10.7 cm flux was 68.7, 68.9, 70.8, 70.1, 70.9, 70.4 and 70.9 with a mean of 70.1. The Estimated planetary A indices were 2, 3, 37, 13, 9, 4 and 8 with a mean of 10.9. The Estimated mid-latitude A indices were 1, 2, 20, 10, 7, 3 and 7 with a mean of 7.1.

Mike Donnelly, KG9M, of Woodstock, Illinois, wrote to ask "What the heck does 'unsettled conditions' really mean? Good for DX or not??? Same question for 'quiet,' too." Unsettled, active and quiet refer to geomagnetic indices, the K index and the A index. We generally want those numbers to be low, or quiet, as absorption is lower and polar propagation paths work better. An exception would be VHF aurora propagation, when the numbers are high.

The effects of geomagnetic activity are much greater when operating from the far north. Sam Vigil, WA6NGH, of San Luis Obispo, California, says that during the summer of 2005, he and his wife Eve, KF6NEV, paddled 720 miles down the Teslin and Yukon rivers from near Whitehorse in Yukon Territory to Circle, Alaska. They brought a 40 meter QRP transceiver and a general coverage shortwave receiver on the trip that ran from July 25 to August 28.

Sam notes there were long stretches when he heard nothing at all on either radio. The latitude ranged from 60.7 degrees north to 65.8 degrees north. He was searching for archives of A and K index for northern latitudes, and noticed that our bulletin -- archived on the ARRL Web site -- only gives a mid-latitude and a planetary number. He will be giving a talk about his trip at Pacificon this weekend and is looking for historical data.

When I checked out this Web Site, I noted that periods of high geomagnetic activity corresponded to periods when Sam heard no signals. The index to watch for far northern latitudes is the college A and K index, which is from a magnetometer at University of Alaska, which is at 68.68 degrees north.

Peter Thulesen, OX3XR, of Nuuk, Greenland (64 deg N, 51 deg W), wanted geomagnetic data that is appropriate for his high latitude. I suggested he look at the recent data updated daily from the Space Weather Prediction Center (SWPC). This is the same source we use for the indices at the end of our bulletin, but we don't list the Alaska college index here.

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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