Ionization- The process by which air becomes conductive. It is caused by a tremendous charge difference between two regions of opposite charge, and in the case of lightning it is the process that starts the discharge. The electrons in the negatively charged region are so strongly attracted to the positively charged region that they begin to move through the air towards the opposing charge and create a conductive channel. The ionized channel is a conducting path for the lightning discharge. Also called electrical breakdown. (See Leader, Stepped leader)