QST de W1AW
Propagation Forecast Bulletin 44 ARLP044
From Tad Cook, K7RA
Seattle, WA October 31, 2003
To all radio amateurs
SB PROP ARL ARLP044
ARLP044 Propagation de K7RA
Solar excitement continued this week. As this bulletin is being written Thursday night, an extreme geomagnetic storm is in progress. The mid latitude K index has been as high as 9, and severe space weather is predicted for the short term. Average daily sunspot numbers more than doubled this week to 201.4. Average daily solar flux was nearly double the previous week at 249. Average daily sunspot numbers for the week as reported in this bulletin have not been this high since the week of November 7-13, 2002, when it was 205.4. For solar flux, we go back to the week of January 24-30, 2002 when the average daily solar flux was 249.6.
On Friday, October 24, a coronal mass ejection swept by earth around 1500z. The planetary K index went as high as 7, and aurora borealis was seen as far as the southern United States. On Sunday, October 26 an X-class solar flare at 0650z was followed by another one twelve hours later at 1850z. On October 28 one of the most powerful solar flares seen in many years hurled a cloud of particles traveling 5,000,000 miles per hour toward earth. This triggered an S-3 class solar radiation storm, and the next day the planetary A index shot up to 189, and mid-latitude A index was 199. On that day, October 29, an intense geomagnetic storm raged in response to a coronal mass ejection that hit earth around 0630z. Another powerful coronal mass ejection hit earth on October 30. Check the web site, http://www.space.com/scienceastronomy/solar_flare_031028.html for a news article on the major flares and resulting storms.
This weekend is the ARRL November CW Sweepstakes. Conditions could be good if the geomagnetic disturbances cool down. Currently the predicted planetary A index for Friday through Monday, October 31 through November 3 is 100, 30, 15 and 15. The latest solar flux forecast for those same days is 265, 260, 255 and 255.
Peter Greene, N2LVI wrote to inquire about when a solar cycle starts and ends. It isn't easy to determine, and usually is some time after the peak or the minimum that we can say when it was, because in order to smooth out the solar cycle so that the peak can be seen, a running average must be run. In addition, a change of sunspot cycles means the polarity of the sunspots change, and spots from both the old and new cycles coexist. A good explanation for this is on this page: http://www.sunspot.noao.edu/PR/answerbook/sunspots.html#q94. Peter also sent us a link to http://www.qsl.net/w2vtm/hf_solar.html where he put up a graphic look at HF propagation and solar indices.
One of our readers has been taking photos of the sun. Jake, N0LX sent along a link to http://hometown.aol.com/n0lx/sun102403.htm showing his photos.
In closing, if the geomagnetic storms calm we could be in for some fantastic conditions, assuming the sunspot numbers stay high. Finally, a couple of graphs show the recent activity here, http://www.dxlc.com/solar/ and here: http://www.wm7d.net/hamradio/solar/index.shtml.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at http://www.arrl.org/tis/info/propagation.html.
Sunspot numbers for October 23 through 29 were 122, 160, 139, 191, 238, 230 and 330, with a mean of 201.4. 10.7 cm flux was 209.3, 190.6, 221.5, 298.3, 257.2, 274.4 and 291.7, with a mean of 249. Estimated planetary A indices were 7, 34, 14, 10, 15, 20 and 189, with a mean of 41.3.