www.strikingimages.com
www.stormguy.com
www.chaseday.com
www.nationalgraphic.com
www.ghcc.msfc.nasa.gov/lisotd_old.html#types
www.ptius.com/pti/consult/dist/gallery/photogallery.htm
Golde, R.H. Lightning. (London, NY: Academic Press Inc, 1977)