From AMS Glossary
Revision as of 19:20, 26 January 2012 by Perlwikibot
The potential difference between the conductive earth and the conductive upper atmosphere, approximately +250 kV.
This voltage difference is maintained by worldwide cloud electrification. Most of the 250 kV is realized well below the formal ionospheric height of maximum ionization because of the rapid increase of electrical conductivity with height in the atmosphere.