EMRFD Message Archive 2843
Message Date From Subject 2843 2009-04-02 14:35:31 jr_dakota OT: Sun has fewest sunspots since 1913, better GPS (Not so great for HF DXing though ...)
WASHINGTON â" The sun has been unusually quiet lately, with fewer sunspots and weaker magnetic fields than in nearly a century. A quiet sun is good for Earth: GPS systems are more accurate, satellites stay in orbit longer; even the effects of manmade global warming are marginally reduced, though just by three-tenths of a degree at most.
It's all a normal part of the strange but regular cycles of the sun's activity. Scientists don't know why it happens, but "for humankind it's probably a good thing," said David Hathaway, chief solar physicist at NASA's Marshall Space Flight Center in Huntsville, Ala.
This lower activity is shrinking our atmosphere a bit, too. Again, not a problem. The sun isn't bombarding the Earth with the usual amount of short-wave radiation that expands the atmosphere. Researchers at the University of Texas in Dallas found the Earth's upper atmospheric boundary at the lowest in the history of the space age. It's about 125 miles lower than normal.
For centuries, people have been counting sunspots, which are cooler, darker areas of intense magnetic fields that form on the sun's surface. The number of sunspots in recent months has been the lowest since 1913, according to NASA. Scientists are looking as far back as the early 1800s for similar quiet periods. They generally last about five years. This quiet spell, which started in 2007, may follow suit.
Scientists last fall were fooled when sunspot activity briefly ramped up and experts figured the quiet cycle was over. They were wrong.
Marc Hairston, a space scientist at UT-Dallas, compared it to the stock market. Just when you think it can't sink anymore, it does.
"This is the lowest we've ever seen," Hairston said of the solar activity. "We thought we'd be out of it by now, but we're not."
Generally sunspots, the easiest measurement of solar activity, follow a predictable 11-year cycle of high, then low, activity.
During the last high solar period, there were sunspots each day â" sometimes hundreds of them â" from January 1998 to February 2004. So far this year, there have been only 14 days with sunspots. The sun is more spot-free now than it was last year when scientists thought solar action had hit bottom.
Thomas Bogdan, director of the National Oceanic and Atmospheric Administration's Space Weather Prediction Center in Boulder, Colo., said solar activity should be increasing "anytime now."
Others think this may be a replay of 1913 or the even deeper solar ditch of 200 years ago, the Dalton Minimum. The deepest ditch of all was in the 1600s.
A deep minimum probably drops global temperatures temporarily about two-tenths to three-tenths of a degree Fahrenheit, not nearly enough to make up for global warming, said Tom Woods of the University of Colorado's atmospheric and space physics lab.
Generally the heating effect from manmade greenhouse gases is 13 times greater than the variations from solar activity, said Ralph Cicerone, president of the National Academy of Sciences and an expert in atmospheric sciences.
Heavy solar radiation slows down electrons and creates radio waves that interfere with the frequencies used by GPS receivers. So during high solar activity peaks, GPS tracking can be off by nearly a football field because of the distortion from receivers to satellites, NOAA's Bogdan said. But during solar minimums like the current one, GPS is accurate to within a foot or so, he said.
The sun's shrinking of Earth's atmosphere reduces the physical drag on satellites and space junk, keeping both the good and the bad in orbit, Hathaway said.
2854 2009-04-03 11:14:15 Graham / KE9H Re: OT: Sun has fewest sunspots since 1913, better GPS JR:
How much did the temperature of the earth drop during the Maunder
Minimum in the 1600's? Associated with mini ice-age in Europe.
How much did the temperature of the Earth rise during preceding warmer
period 800-1400AD when Greenland coast was actually green, colonized,
and named by the Norse?
2856 2009-04-03 13:12:51 jr_dakota Re: OT: Sun has fewest sunspots since 1913, better GPS Heck I don't know, in fact I didn't really pay that much attention to that part of the article .... I posted it as an article about (lack of) sunspots and RF propagati 2857 2009-04-03 13:56:22 Dave - WB6DHW Re: OT: Sun has fewest sunspots since 1913, better GPS It turns out that global temperatures are directly related to the
sunspots. At least one forcast made in 2003 says cycle 24 will be very
low and cycle 25 sunspots will be non-existent, much like the Maunder
minimum. Has to do with the influence of Jupiter and the other large
planets on the suns rotation on its axis.
Dave - WB6DHW
> Heck I don't know, in fact I didn't really pay that much attention to that part of the article .... I posted it as an article about (lack of) sunspots and RF propagati