transition layer

1. The thin layer that separates thicker layers of different characteristics.
2. The capping inversion or entrainment zone at the top of the convective mixed layer.
   
3. The statically stable layer near the base of convective clouds in the Tropics.
   
4. A stratified layer of a body of water between the mixed layer and the undisturbed fluid beneath it; it refers to the uppermost (closest to the surface) thermocline at any given time.