of an air parcel at the 700 hPa pressure level, and is the potential temperature at the surface.

It was first introduced as a simple but useful measure of the strength of the inversion that caps the planetary boundary layer on earth, and also indicates the level of convective stability of an air column at a given location. Regions with negative LTS have a larger potential temperature on the surface than in the mid-troposphere, which makes the air column unstable and encourages convection. There