Can you say "Maunder Minimum"? "Little-Ice-Age"? - HLG
Are Sunspots Disappearing?
Based on a science@NASA release
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Summary: The Sun is in the deepest solar minimum in nearly a century. Some observers are starting to wonder, are sunspots disappearing? Sunspots can have profound effects on the Earth's climate as well as human and satellite missions in orbit.
Sunspots as darkened knots of magnetic energy and rising hot plasma. Credit: SOHO
The Sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?
"Personally, I'm betting that sunspots are coming back," says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, "there is some evidence that they won't."
Penn's colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline.
"Sunspot magnetic fields are dropping by about 50 gauss per year," says Penn. "If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015."
Sunspot magnetic fields measured by Livingston and Penn from 1992 - Feb. 2009 using an infrared Zeeman splitting technique.
This disappearing act is possible because sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the Sun's interior. If Earth lost its magnetic field, the solid planet would remain intact, but if a sunspot loses its magnetism, it ceases to exist.
"According to our measurements, sunspots seem to form only if the magnetic field is stronger than about 1500 gauss," says Livingston. "If the current trend continues, we'll hit that threshold in the near future, and solar magnetic fields would become too weak to form sunspots."
"This work has caused a sensation in the field of solar physics," comments NASA sunspot expert David Hathaway, who is not directly involved in the research. "It's controversial stuff."
The controversy is not about the data. "We know Livingston and Penn are excellent observers," says Hathaway. "The trend that they have discovered appears to be real." The part colleagues have trouble believing is the extrapolation. Hathaway notes that most of their data were taken after the maximum of Solar Cycle 23 (2000-2002) when sunspot activity naturally began to decline. "The drop in magnetic fields could be a normal aspect of the solar cycle and not a sign that sunspots are permanently vanishing."
Penn himself wonders about these points. "Our technique is relatively new and the data stretches back in time only 17 years. We could be observing a temporary downturn that will reverse itself."
Zeeman splitting of spectral lines from a strongly-magnetized sunspot.
The technique they're using was pioneered by Livingston at the McMath-Pierce solar telescope near Tucson. He looks at a spectral line emitted by iron atoms in the Sun's atmosphere. Sunspot magnetic fields cause the line to split in two—an effect called "Zeeman splitting" after Dutch physicist Pieter Zeeman who discovered the phenomenon in the 19th century. The size of the split reveals the intensity of the magnetism.
Astronomers have been measuring sunspot magnetic fields in this general way for nearly a century, but Livingston added a twist. While most researchers measure the splitting of spectral lines in the visible part of the Sun's spectrum, Livingston decided to try an infra-red spectral line. Infrared lines are much more sensitive to the Zeeman effect and provide more accurate answers. Also, he dedicated himself to measuring a large number of sunspots—more than 900 between 1998 and 2005 alone. The combination of accuracy and numbers revealed the downturn.
If sunspots do go away, it wouldn't be the first time. In the 17th century, the Sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the Sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.
"Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," Livingston and Penn caution in a recent issue of EOS. "Other indications of solar activity suggest that sunspots must return in earnest within the next year."
Solar activity tends to peak on roughly an 11-year cycle.
Credit: SOHO
Whatever happens, notes Hathaway, "the Sun is behaving in an interesting way and I believe we're about to learn something new."
Solar activity can have a profound effect on the Earth's climate and biosphere. For instance, some studies indicate that sunspot activity could be linked to weather patterns on Earth. Understanding the behavior of the Sun can help scientists determine what effects the solar cycle will have on Earth in the years to come
2 comments:
As a geologist I am very comfortable with the multiple working hypothesis - I would like someone to start publicizing the other ideas out there. The Danes have been on the case for a long while, studying the sun; who would have thought the sun would be involved in warming? The first paper to read is Friis-Christensen and Lassen (Science; 1991) If you can find the entire issue in the reference library, you will see the editors comment referred to this paper as hitting the ball into the anthropogenic court. The causation is under scientific review, however, and while the radiation from the sun varies only in the fourth decimal place, the magnetism is awesome.
The important correlation between warming and cooling is the sunspot peak frequency, not the actual number of spots. However, we all realize correlation is not causation. Sunspot peak frequency proxies for the rise and fall of the sun’s magnetic field. Cosmic radiation is currently at its highest ever measured because the sun and earth’s magnetic shields is down; climate is changing. The climate celebrities, however, are linking climate and the carbon economy. Maybe not evil; just wrong.
The third ranking gas is CO2 (0.0383%), and it does not correlate well with global warming or cooling either; in fact, CO2 in the atmosphere trails warming which is clear natural evidence for its well-studied inverse solubility in water: CO2 dissolves rapidly in cold water and bubbles rapidly out of warm water. CO2 has been rising and Earth and her oceans have been warming. However, the correlation trails.
Svensmark of the Danish National Space Center has experiments scheduled for the Hadron collider to test his basement experiment. Elevated solar flux (> 10 protons per cc) appears to cause fog in the Great Lakes and clouds too. The hypothesis of the Danish National Space Center goes as follows: quiet sun allows the geomagnetic shield to drop. Incoming galactic cosmic ray flux creates more low-level clouds, more snow, and more albedo effect as more is heat reflected resulting in a colder climate. Active sun has an enhanced magnetic field which induces Earth’s geomagnetic shield response. Earth has fewer low-level clouds, less rain, snow and ice, and less albedo (less heat reflected) producing a warmer climate.
That is how the bulk of climate change likely works, coupled with (modulated by) sunspot peak frequency there are cycles of global warming and cooling like waves in the ocean. When the waves are closely spaced, all the planets warm; when the waves are spaced farther apart, as they have been for this century, all the planets cool.
Many answers yield many new questions: the change in cloud cover is only a small percentage, and the ultimate cause of the solar magnetic cycle may be cyclicity in the Sun-Jupiter centre of gravity. We await more on that.
Although the post 60s warming period appears to be over, warming and attendant humidity have allowed the principal green house gas, water vapour, to kick in with more clouds, rain and snow depending on where you live to provide the negative feedback that scientists use to explain the existence of complex life on Earth for 550 million years. We can likely kick much of the carbon economy sometime late the twenty-first century, but we must not rush to judgement for the wrong reason. The planet heats and cools naturally and our gasses are the thermostat. Nothing unusual is going on except for the Orwellian politics.
Correlation is not causation? Wow, that is profound! So, how long have you been able to meauser the solar flux to the "4th decimal place"? Where are those numbers during the Maunder Minimum? What "thermostat gases" varied so suddenly during the Little Ice Age to cause the sudden cooling that WAS corelated with the minimum in solar activity? You casually duck that issue, of course. What dramatic flux in "thermostat gasses" lead to the Younger-Dryas? Please provide that data, with measurements to the "4th decimal place"! - HLG
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