Solar wind

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The ideas of Fitzgerald and others were further developed by the Norwegian physicist Kristian Birkeland. His geomagnetic surveys showed that auroral activity was nearly uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". In 1916, Birkeland was probably the first person to successfully predict that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds". In other words, the solar wind consists of both negative electrons and positive ions .Three years later in 1919,Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun

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However, the acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. The first numerical simulation of the solar wind in the solar corona including closed and open field lines was performed by Pneuman and Knopp in 1971. The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration

 

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.

In 1990, the Ulysses probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's ecliptic plane

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Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space (as seen during total eclipses). Later spectroscopic work confirmed this extraordinary temperature. In the mid-1950s the British mathematician Sydney Cgapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, a German scientist named Ludwing Biermann became interested in the fact that no matter whether a comet is headed towards or away from the Sun, its tail always points away from the Sun. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away.Wilfried Schröder claims in his book, Who First Discovered the Solar Wind?, that the German astronomer Paul Ahnert was the first to relate solar wind to comet tail direction based on observations of the comet Whipple-Fedke

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