Diagnostic determination of mixing layer height and entrainment layer thickness in the convective boundary layer using a spectral entraining jet model

Abstract

Simple parcel theory is known to fail for the determination of the entrainment layer thickness (ELT) in the convective boundary layer (CBL). In this paper a new semi-empirical method is proposed to diagnose the mixing layer height (MLH) and ELT under convective conditions from an ensemble of individual rising air parcels. The model combines a statistical description of the generation of warm updrafts within the surface layer (SL), and a simple one-dimensional entraining jet model for the determination of the height of updraft tops. It considers dynamical, thermodynamical as well as microphysical processes of entraining jets. The model is validated using measurements from the SANA experiment and compared to different diagnostic parameterizations of the ELT. The ELT from the new model agrees well with sodar measurements as well as with parameterized values. Observed differences are discussed. The method proposed here overcomes the shortcomings of simple parcel theory and allows the determination of the ELT by a more sophisticated thermodynamic approach.