SB PROP @ ARL $ARLP012<br />ARLP012 Propagation de K7RA<br /><br />ZCZC AP12<br />QST de W1AW <br />Propagation Forecast Bulletin 12 ARLP012<br />>From Tad Cook, K7RA<br />Seattle, WA March 21, 2003<br />To all radio amateurs <br /><br />SB PROP ARL ARLP012<br />ARLP012 Propagation de K7RA<br /><br />This has been quite a week for geomagnetic storms. The average daily<br />planetary A index, a measure of geomagnetic activity averaged over<br />24 hours from the planetary K indices in the same period, was about<br />20 points higher this week than last. This was caused by a near<br />constant strong solar wind accompanied by solar flares.<br /><br />The worst or most active day was Monday when the planetary A index<br />was 39 and the higher latitude college A index (measured in Alaska)<br />was 78. The college K index was as high as 8, indicating a severe<br />geomagnetic storm near the polar region.<br /><br />For an explanation of the relationship between K and A indices,<br />check
http://www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html. Looking at<br />the chart you can see that if the K index of 8 persisted for 24<br />hours, this would produce an A index of 207, almost unheard of.<br />Fortunately mid-latitude numbers weren't as bad.<br /><br />Solar flux and sunspot numbers declined this week over last.<br />Average daily sunspot numbers dropped nearly 82 points to 92, and<br />solar flux was down by over 14 points. This is expected to continue,<br />with solar flux below 100 through the middle of next week.<br /><br />Unsettled to active geomagnetic conditions also should continue, at<br />least over the next few days. Solar flux and sunspot numbers were<br />better over the last few years around this date. Average daily<br />sunspot numbers were 134.3 in 2002, 101.7 in 2001 and 183.3 in 2000<br />during this week. Average daily sunspot numbers were 180.9 in 2002,<br />144.2 in 2001 and 207.8 in 2000.<br /><br />The spring equinox begins today. Spring is a great time for HF<br />propagation, with all points on the earth today getting about 12<br />hours of sunlight. There actually is some variation in day length on<br />this day, dependent on the observer's latitude. This is explained by<br />the U.S. Naval Observatory at<br />
http://aa.usno.navy.mil/faq/docs/equinoxes.html.<br /><br />For more information about propagation and an explanation of the<br />numbers used in this bulletin see the Propagation page on the ARRL<br />Web site at
http://www.arrl.org/tis/info/propagation.html.<br /><br />Sunspot numbers for March 13 through 19 were 88, 114, 124, 121, 80,<br />64, and 53, with a mean of 92. 10.7 cm flux was 134.2, 138.9, 130.7,<br />128.6, 164.1, 118.4, and 108.2, with a mean of 131.9. Estimated<br />planetary A indices were 15, 25, 24, 23, 39, 26, and 14, with a mean<br />of 23.7.<br />NNNN<br />/EX
