The K7RA Solar Update
This week we saw only one sunspot, number 997, and only on Memorial Day, May 26. Alas, this was another sunspot left over from fading Solar Cycle 23 and its appearance was very brief. One day it weakly emerged, it quickly faded from view. The previous five days were spotless; spots appeared on the five days prior to that, and previous to those spotted days were 10 days of no spots. Sunspot numbers for May 22-28 were 0, 0, 0, 0, 12, 0 and 0 with a mean of 1.7. The 10.7 cm flux was 69.3, 67.8, 68.5, 68.3, 68, 67.9 and 67.8 with a mean of 68.2. Estimated planetary A indices were 9, 10, 7, 6, 4, 3 and 12 with a mean of 7.3. Estimated mid-latitude A indices were 7, 7, 4, 7, 3, 2 and 10, with a mean of 5.7.
If our Sun shows no more sunspots today and tomorrow, May 30-31, we will see a 3 month average of daily sunspot numbers centered on April -- just above the values for every 3 month average since the minimum, centered on October 2007. The values through April are 3, 6.9, 8.1, 8.5, 8.4, 8.4 and 8.9. Because this is a three month average, we won't know the value centered on May until the end of June.If these numbers suggest Solar Cycle 24 is stalled, we can compare with the previous minimum.
Using the same scheme, the 3 month averages of daily sunspot numbers centered on September 1996-March 1997 (this includes all the sunspot data from August through the following April) were 8.7, 10.2, 14.2, 16.4, 11.7, 11.3 and 16.4.
Those are slightly higher values 11 years ago compared with the current numbers, but notice the six months following the minimum also seemed to flatten out. And while the last bottom had slightly higher average sunspot numbers, it had one longer period of no spots. If we rank periods of spotless days back to the mid-nineteenth century, the period between Solar Cycles 22 and 23 had the 10th ranked spotless days period -- the 42 days from September 13-October 24, 1996. Now between Cycles 23 and 24, we have observed two stretches of spotless days of at least three weeks, a fifty-third ranked 22 days in September, and the twenty-ninth ranked 28 days in October and November of last year.
The three longest spotless periods since the mid-nineteenth century were 92 days leading up to Solar Cycle 15 in 1913 -- 69 days prior to Cycle 14 in 1901, and 54 days before Cycle 12 in 1879. You can peruse the 72 longest periods of zero sunspots lasting 20 days or more, all ranked from longest to shortest, here.
Recently we offered notes from Dr Kenneth Tapping that showed why he doesn't think this minimum is unusual. Anyone who sends a blank e-mail can receive these notes. So far, the response has been huge, with more than 900 requests, and the offer still stands.
Dr Tapping is an astrophysicist at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, British Columbia. They supply the world with their daily 10.7 cm solar flux readings, also reported here.
The notes were offered after Dr Tapping was widely misquoted several months ago on various Web sites. A source claimed Dr Tapping foresaw the possibility of decades of no sunspots and then tried to link this to several sorts of worldwide calamity. Some pieces even claimed that the sunspot cycle hit bottom a year and a half ago, and that no sunspots have been observed since -- a false claim easily refuted by existing data, widely available.
Last week this bulletin mentioned a free downloadable copy of Bob Brown's Little Pistol's Guide to HF Propagation, but it seems it isn't free after all. I knew the book was out of print, and had seen the PDF version at the Web address I gave for so long that I wrongly assumed downloading this was legal, but apparently not. It is actually still being published as the same PDF document on a CD ROM produced by World Radio magazine. It is available for purchase.
Expect more of the quiet geomagnetic conditions seen recently for the next week. The US Air Force and NOAA Space Weather Prediction Center predict planetary A index beginning May 30 at 10, 8, 10, 10 and then 5 from June 3-14. They also predict the next period when daily solar flux is above 70 to be June 12-20. Geophysical Institute Prague foresees unsettled conditions May 30-31, unsettled to active June 1, unsettled June 2, quiet to unsettled June 3 and quiet conditions June 4-5.
Currently we are just a few weeks away from the summer solstice, the longest day of the year. This officially occurs at midnight GMT on June 21. Our current sporadic-E season continues, with often unexpected openings on 6 and 10 meters.
Ray Soifer, W2RS, at his Texas vacation home observed 6 meter openings from EM00 to Colorado, Illinois, Tennessee and Mississippi. During last weekend's WPX contest using 100 W and a very simple antenna, he worked all continents on 20 meters in just 25 minutes on Saturday at 2220-2245 UTC.
Joaquin Montoya, EA2CCG, from Spain reports great openings from his mobile on 6 and 10 meters on Saturday, including 10 meter FM into Europe. On mid-day Saturday he worked 27 stations in Europe on 6 meters with great signals, and he heard a very strong signal from an EA8 in Africa. The next day, 10 meters was open again, although not as strong, but 6 meters was not.
Julio Medina, NP3CW, in San Juan, Puerto Rico, reported great conditions on 6 meters on May 22-23, working many stations across the US and into South America, Mexico and the Caribbean.
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.