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Unformatted text preview: The solar wind as a fluid It is important when looking at the behaviour of the solar wind to know whether we have to treat it as individual particles, or whether we can treat it as a fluid (which makes calculations of its bulk behaviour much simpler). To decide on this we need to know on what scale sizes the particles interact. Here the concept of the "effective mean free path" is important. A particle entering a group of others must be affected if we are to assume it acts as a fluid - seen from far away its properties are altered: this is the concept of LOCALIZATION. From standard gas theory you will remember that the mean free path of a particle is the average distance it goes between collisions. As a very rough approximatin we can say that at distance scales over this we can consider this we can consider the particles as a fluid, since they interact by collisions and this "spreads" effects between them at scales larger than those in which they collide. At scale sizes below the mean free path we have to deal with individual particles. For a collide....
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- Fall '10