Boyden index
From Glossary of Meteorology
A measure of the mean thermodynamic stability in a layer beneath 700 mb.
The Boyden index is given by I-Z-T-200, where I is the Boyden index, Z is the 1000–700- mb thickness in dam, and T is the 700-mb temperature in °C.
Boyden, C. J. 1963. Meteor. Mag.. 92. 198–210.