The height above ground level at which there is change in sign of the normal temperature
'
lapse rate',

(the rate of change of the temperature with height). Several temperature inversions
may be present in the air over a given site at different altitudes as result of various
meteorological factors.
Source:
PAC, 1990, 62, 2167
(Glossary of atmospheric chemistry terms (Recommendations 1990))
on page 2197