QST de W1AW
Propagation Forecast Bulletin 11 ARLP011
From Tad Cook, K7RA Seattle, WA March 9, 2007
SB PROP ARL ARLP011
ARLP011 Propagation de K7RA
On March 1 sunspot 944 was pointed straight at us. It was a small sunspot, followed a few days later by another small spot, 945. Sunspot 945 is visible in photos from March 5, just behind 944, but both spots seemed to disappear a day or two later, before they would have rotated off the visible solar disk. Now the Sun is blank, and the sunspot number is zero.
The minimum non-zero sunspot number is 11, and lately sunspot numbers move from 0 to 11 to 23 or 24, and back to 11. No solar activity is expected for the next few days, so we will probably see at least several days with a zero sunspot number. Geomagnetic conditions are expected to remain quiet, at least until Monday or Tuesday, March 12-13. The USAF predicts a Planetary A index for March 9-15 of 5, 5, 7, 15, 20, 15 and 10. Geophysical Institute Prague predicts quiet conditions for March 9-10, quiet to unsettled March 11, active geomagnetic conditions for March 12, unsettled to active March 13, unsettled March 14 and quiet to unsettled March 15. A recurring solar wind stream is predicted for Monday, March 12, and should produce the expected geomagnetic instability.
New predictions for the solar minimum are coming frequently of late. The monthly smoothed sunspot number forecast for the rest of 2007 from the NOAA Space Environment Center in the weekly Preliminary Report and Forecast has been adjusted again, the third time since the first of the year. The revised tables are on page 9 of issue 1635, and page 10 of issues 1640 and 1644 at, http://www.sec.noaa.gov/weekly/index.html (the table in 1640 is mislabeled at the bottom of the page as 03 January when it is really 06 February). Currently they predict a solar minimum for right now, with a smoothed sunspot number of 6 for March and April 2007, then 7, 8, 10, 11, 13, 16, 18 and 21 for the remaining eight months of this year.
As mentioned in past bulletins, these are smoothed sunspot numbers, averaged over a year. So the prediction of 6 for this month means that if the prediction is accurate, at the end of September 2007 you could take half the average of daily sunspot numbers for that month, add it to half the average of daily sunspot numbers for September 2006, add the total to the monthly averages for each month in between, divide by 12, and get 6 as the result. Currently we're seeing higher values, with an average daily sunspot number of 19 for last week, 19.6 the week before, 14.6 for the week prior to that, 6.3 for the previous week, and 28.7 for the week prior to that, which was February 1-7.
You can see an explanation of the method for determining the 12 month smoothed sunspot number at, http://www.ngdc.noaa.gov/stp/IONO/sunspot.html.
Jim Headrick, W3CP of Stanfield, Oregon sent in a different prediction from the Australian government. It has the solar minimum centered on September 2007, and you can see it at, http://tinyurl.com/2ymk92. Note that the NOAA version mentioned previously ends in December 2007, but the one Jim sent goes through 2008 and 2009 as well. By the way, I don't know how long Jim has been a ham, but he was born early in sunspot cycle 15, and I'm sure he hopes to see the new cycle 24 all the way through. See a page of all the 20th century sunspot cycles at, http://wm7d.net/hamradio/solar/historical.shtml.
We heard from another ham enjoying low power operations at the bottom of the cycle. Bill Raiford, NI4Y of Fredericksburg, Virginia says he operates 10 watts on 20 meters from his car. Bill says, "Last week I worked VK2KM and this week I worked VK2GWK from my 10 watt mobile station. No, VK isn't rare DX, but just the thought of 10 watts propagating from my vehicle in VA to VK land is quite amazing. I am at 194 countries from my mobile."
Dave Green, VE5TLY of Ottawa, Ontario sent an interesting link from the BBC concerning the new STEREO (Solar Terrestrial Relations Observatory) satellites which will soon be observing coronal mass ejections traveling through space in 3D. Read the article at, http://news.bbc.co.uk/2/hi/science/nature/6411349.stm.
If you would like to make a comment or have a tip for our readers, email the author at, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL Technical Information Service at, http://www.arrl.org/tis/info/propagation.html. For a detailed
explanation of the numbers used in this bulletin see, http://www.arrl.org/tis/info/k9la-prop.html. An archive of past propagation bulletins is at, http://www.arrl.org/w1aw/prop/.
Monthly propagation charts between four USA regions and twelve overseas locations are at, http://www.arrl.org/qst/propcharts/.
Sunspot numbers for March 1 through 7 were 11, 23, 11, 24, 27, 26 and 11 with a mean of 19. 10.7 cm flux was 74.8, 75.5, 73.3, 72.5, 71.9, 71.9, and 72.9, with a mean of 73.3. Estimated planetary A indices were 11, 5, 2, 3, 8, 18 and 14 with a mean of 8.7. Estimated mid-latitude A indices were 7, 4, 0, 4, 6, 14 and 12, with a mean of 6.7.
