|MadSci Network: Earth Sciences|
Here are two websites that will (I hope) answer your question. Just one point of clarification: no mass is transferred in a lightning stroke. First, protons have no involvement in lightning - we are dealing entirely with ionized atoms (those which have lost electrons and hence are positively charged), and free electrons. The electrons themselves travel from atom to atom as the lightning stroke takes place, exactly as they would in an electrical cord. http://www.lightningrod.com/manual5_how.html http://www.lightningstorm.com/lightningstorm/learning/index.jsp
Try the links in the MadSci Library for more information on Earth Sciences.