There are two types of frontal surface. One of them is conspicuous on the ground and loses its frontal characteristic with the increase of height, while in the other no conspicuous front is recognizable on the ground, but with the increase of height the disparity of temperature becomes larger.
The authors calculated the energy releasable from such horizontally labile situations, adopting the idealized models of the above two frontal surfaces.
The result shows that the former type of frontal surface is more horizontally labile than the latter, though the difference is small.