We now leave theory for a moment to discuss a little what goes on in the real world. Temperature lapse-rates are often expressed in terms of a decline in temperature as a function of altitude. In reality though, it turns out that pressure is a more convenient vertical coordinate to use. From soundings one finds the following approximate relation between temperature and pressure:
The Theta symbol stands for the ground temperature. This is better confirmed by soundings than the dry adiabatic lapse rate expressed in terms of altitude as
dT/dz = -g/Cp.
It is worthwhile to think for a moment what it means.