Vavrek, R. J.; Kithil, R.; Holle, R. L.; Allsopp, J.; Cooper, M. A. (17 July 2006) [4 April 2006]. "Section 6.1.8: The Science of Thunder". National Lightning Safety Institute. Archived from the original on 17 July 2006. Retrieved 11 June 2022.
Vavrek, R. J.; Kithil, R.; Holle, R. L.; Allsopp, J.; Cooper, M. A. (17 July 2006) [4 April 2006]. "Section 6.1.8: The Science of Thunder". National Lightning Safety Institute. Archived from the original on 17 July 2006. Retrieved 11 June 2022.