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Sunspot counts for 2009 have dropped even lower. As of yesterday, no sunspots had been observed on 78 of the year's 90 days (87%). "We're experiencing a very deep solar minimum," says solar physicist Dean Pesnell of the Goddard Space Flight Center. "This is the quietest sun we've seen in almost a century," agrees sunspot expert David Hathaway of the Marshall Space Flight Center. Quiet suns are a natural part of the sunspot cycle; they come along every 11 years or so. “Sunspots are planet-sized islands of magnetism on the surface of the sun; they are sources of solar flares, coronal mass ejections and intense UV radiation. In the past, peaks of solar activity were always followed by valleys of relative calm—a clockwork pattern that has held true for more than 200 years. “The current solar minimum is part of that pattern. In fact, it's right on time. "We're due for a bit of quiet—and here it is," says Pesnell. “But is it supposed to be this quiet? “In 2008, the sun set the following records: “A 50-year low in solar wind pressure: Measurements by the Ulysses spacecraft reveal a 20% drop in solar wind pressure since the mid-1990s—the lowest point since such measurements began in the 1960s. The solar wind helps keep galactic cosmic rays out of the inner solar system. With the solar wind flagging, more cosmic rays are permitted to enter, resulting in increased health hazards for astronauts. Weaker solar wind also means fewer geomagnetic storms and auroras on Earth. This is one of the points of my
new book “Magnetic Reversals and “A 12-year low in solar "irradiance": Careful measurements by several NASA spacecraft show that the sun's brightness has dropped by 0.02% at visible wavelengths and a whopping 6% at extreme UV wavelengths since the solar minimum of 1996. These changes are not enough to reverse the course of global warming, but there are some other, noticeable side-effects: Earth's upper atmosphere is heated less by the sun and it is therefore less "puffed up.” Not enough to change the course of
global warming? Unless, of course, A 55-year low in solar radio emissions: After World War II, astronomers began keeping records of the sun's brightness at radio wavelengths. Records of 10.7 cm flux extend back all the way to the early 1950s. Radio telescopes are now recording the dimmest "radio sun" since 1955. Some researchers believe that the lessening of radio emissions is an indication of weakness in the sun's global magnetic field. No one is certain, however, because the source of these long-monitored radio emissions is not fully understood. All these lows have sparked a debate about whether the ongoing minimum is "weird", "extreme" or just an overdue "market correction" following a string of unusually intense solar maxima. "Since the Space Age began in the 1950s, solar activity has been generally high," notes Hathaway. "Five of the ten most intense solar cycles on record have occurred in the last 50 years. We're just not used to this kind of deep calm." "Five of the ten most intense solar
cycles on record have occurred in “Deep calm was fairly common a hundred years ago. The solar minima of 1901 and 1913, for instance, were even longer than the one we're experiencing now. To match those minima in terms of depth and longevity, the current minimum will have to last at least another year. “Modern technology cannot, however, predict what comes next. Competing models by dozens of top solar physicists disagree, sometimes sharply, on when this solar minimum will end and how big the next solar maximum will be. No one fully understands the underlying physics of the sunspot cycle. “Pesnell believes sunspot counts will pick up again soon, "possibly by the end of the year," to be followed by a solar maximum of below-average intensity in 2012 or 2013. But like other forecasters, he knows he could be
wrong. Stay tuned for updates.”
http://science.nasa.gov/headlines/y2009/01apr_deepsolarminimum.htm?list878321 |
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