Residual layer

From Glossary of Meteorology

residual layer

The middle portion of the nocturnal atmospheric boundary layer characterized by weak sporadic turbulence and initially uniformly mixed potential temperature and pollutants remaining from the mixed layer of the previous day.

Below the statically neutral residual layer is the stable boundary layer in contact with the radiatively cooled ground, and above it is the capping inversion that separates boundary layer air from free-atmosphere air.