article_snippet.sent: As they develop, air acts as an insulator between the positive and negative charges in the cloud, and between the cloud and the ground.
article_snippet.sent: Positive charge builds up in one area of the cloud, while negative charges build up in the other - typically the top and bottom of the cloud respectively.
article_snippet.sent: As negative charges gather in the bottom of a cloud, the negative charges in the ground are forced from the surface, leaving the negative charges in the ground positive.
article_snippet.sent: When a so-called 'streamer' of negative charges leaps from the bottom of the cloud, When a so-called 'streamer' of negative charges leaps from the bottom of the cloud is therefore attracted to the ground, which in turn emits a streamer of positive charges from the ground up.
article_snippet.sent: As they develop, air acts as an insulator between the positive and negative charges in the cloud, and between the cloud and the ground. 
article_snippet.sent: When a so-called 'streamer' of negative charges leaps from the bottom of the cloud, it is attracted to the ground, which in turn emits a streamer of positive charges from the ground up.