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Last month, data from the joint National Aeronautics and Space Administration and European Space Agency Ulysses solar mission revealed that the solar wind is at a 50-year low, potentially opening up the solar system to more dangerous rays from outer space.Researchers were not surprised that the solar wind has decreased. In fact, the amount of radiation sent off by the sun operates in an 11-year cycle, but this dip was lower than those recently observed. Still, it may be in line with centuries-long patterns, said Nancy Crooker, a research professor at Boston University.
In the late 1990s the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the sun, and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about 4 solar radii from the photosphere; but the transition (or "sonic point") now appears to be much lower, perhaps only 1 solar radius above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the sun.