In a book I have read that in the Van-Allen-Belt there are the protons and electrons from the solar wind.
What I do not get, is why they should behave that way illustrated in this image. Why should the protons be closer to Earth and the electrons farther away? And why should they bounce from pole to pole?

![Van-Allen-Belt][1]


  [1]: https://i.sstatic.net/ih8bU.jpg