The Solar Wind - often cascades of particles caused when...

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The Solar Wind Early evidence of the Solar Wind Before the satellite age and the ability to measure the interplanetary medium directly there were two pieces of evidence that some sort of solar wind existed. (The solar wind in this case would be a tenuous atmosphere of the sun that permeated the spaces between the planets, and moving outwards from the sun.) The first piece of evidence came from Cosmic Rays. Cosmic Ray Modulation In 1912 Victor Hess discovered a "weak but penetrating" radiation which increased with height. It was soon realised this came from outside the Earth, and the term "cosmic rays" coined to describe it. It was also soon realised it comprised of high-energy particle injection, where the particles were mainly protons, electrons and neutrons, with energies from 10's of MeV to many GeV. It has further been discovered that these comprise two types - particles of solar origin (generally the lower energy ones) and those of "galactic" origin - i.e from outside the solar system. What we see at ground level are not generally the primary particles but secondaries -
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Unformatted text preview: often cascades of particles caused when the primary particles collide with the atmosphere. If the strength of the galactic cosmic ray influx is measured over a period os measured over a period of time we find that it varies with the solar cycle, only with the opposite phase to solar radiation fluxes like the 10.7 cm flux: This decrease of the cosmic ray flux at solar maximum is known as the "Forbush Decrease" after its discoverer. It is seen to be more marked with altitude. It is believed this is due to the modulation of galactic cosmic rays by the solar wind and Interplanetary Magnetic Field as they diffuse inwards from the heliopause. The stronger the solar wind/IMF, the more the particles diffuse and effectively deflected away from the inner solar system. This effect is so marked that it is thought that cosmic ray detection on the Pioneer spacecraft might have been a better way of detecting the heliopause than direct measurement of the organisation of the solar wind particles....
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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