The K7RA Solar Update


Our Sun is in the news again, unfortunately not due to any hoped-for activity, but for the eerie quiet instead. The Sun is surprisingly calm by several measurements -- including the large number of spotless days -- with an average 10.7 cm solar flux and low solar wind pressure.

According to an April 1 release from NASA (that I wish was just an April Fool's Day joke), we are witnessing a 50 year low in solar wind pressure -- a 20 percent drop since the mid 1990s. Of course the advantage to this is geomagnetic storms are very rare. But that is a disadvantage for VHF operators who enjoy using aurora to propagate radio waves. The news release claimed that the 10.7 cm solar flux is at a 55 year low, although this figure has only been tracked for the past 65 or so years. They also tell us that 2008 had more spotless days than any year since 1913.

In this bulletin, we have calculated a running 3 month average sunspot number; the average for January-March -- centered on February at 2.1 -- was the lowest 3month average since July and August of 2008.

Here are the averages since January 2007:

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 3.0
Nov 07 6.9
Dec 07 8.1
Jan 08 8.5
Feb 08 8.4
Mar 08 8.4
Apr 08 8.9
May 08 5.0
Jun 08 3.7
Jul 08 2.0
Aug 08 1.1
Sep 08 2.5
Oct 08 4.5
Nov 08 4.4
Dec 08 3.7
Jan 09 2.3
Feb 09 2.1

Using this table, we have been fooled before, thinking that an up-trend would continue. Take a look at the periods centered on October 2007 or August 2008.

The first bulletin of 2008 noted that one year prior we commented that 2007 would likely see the transition from Solar Cycle 23 to 24. Then in the fifth bulletin of last year, we saw that uptick in the 3 month moving average, suggesting that the new cycle was commencing. The same bulletin noted that four years prior to that, a reader asked if we might be at the end of Solar Cycle 23. We've looked at various predictions for the next cycle, and that same NASA article referenced above has a plot of the various predicted maxima. Quite a range! At one time we were excited by the prediction of Dikpati et al, because it foretold a robust Solar Cycle 24. But note in the chart (that you can zoom in on by clicking) there were actually four predictions more optimistic that her team's projection. My favorite -- since it is the most wildly optimistic -- is the 2005 forecast by Horstman that crunched data from the last five solar cycles, starting with 19, of course, for a sunspot peak of 185 in 2010 or 2011.

Right now there are no sunspots, but the 10.7 cm solar flux is up a bit lately. The latest prediction has the usual quiet planetary A index at 8 for April 3-4, then back to 5, then 15 and 10 for April 9-10. Predicted solar flux is 71 for April 3-9, then back to 70 for April 10-22 then to 72 for April 23 and into May. Sunspot numbers for March 26-April 1 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 69.1, 71.6, 70.6, 70.9, 70.9, 71.2 and 70.8 with a mean of 70.7. The estimated planetary A indices were 7, 4, 4, 5, 4, 4 and 4 with a mean of 4.6. The estimated mid-latitude A indices were 6, 2, 2, 4, 3, 2 and 3 with a mean of 3.1.

Recent mail indicates operators are still enjoying the HF bands, even without sunspots. Matthew Chambers, W1JEQ, of Newark, Missouri, said he had fun working HI3TEJ, ZW5B, YW4D, PY6HD and several US stations in a recent DX contest, using just a barefoot transceiver and a 20 meter monoband mobile whip attached to a fire escape. He notes, "If this is what zero sunspots can sound like, then I can't wait to hear the bands with sunspots!"

Tim Hickman, N3JON, of Timonium, Maryland, wrote: "After a more quiet-than-normal week, if that is even possible, the bands were popping late afternoon and early evening on Thursday April 2, 2009. On 20 meters, strong signals from CN8KD at 2100 show up in Maryland, then VKs and JA start showing up on 20 meters, then 2 hours later, AG1AB is working the East Coast with solid 59s on 40 meters. The spotter's net reports start showing up of DX on 10 meters that I can hear, but not well enough to work. It was nice to see the bands come alive at least for a moment -- we all can hope this is the harbinger of things to come!

Russ Ward. W4NI, of Nashville, Tennessee, likes the new book Midlatitude Ionospheric Dynamics and Disturbances by Kintner and Coster, although he says it is very advanced and notes it is "not for the unmotivated. I noticed also that the book is very expensive."

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.