A Variant of Modification of Monin–Obukhov Similarity Theory with a Threshold Two-Layer Turbulence Model for the Convective Surface Layer

A double‑layered model of the convective atmospheric surface layer (ASL) with a fixed in-ter‑layer boundary is considered. It enables the approximation of a family of turbulent moments by one‑parameter relations and has clear physical justification. The ASL is assumed to consist of a frictional‑heat sublayer, adjacent to the underlying surface, and a sublayer of forced con-vection. The inter‑layer boundary is fixed and is associated with the bifurcation level that marks the emergence of coherent structures of small convective thermals within the turbulent surface layer. Approximations of the turbulent moments are derived independently for each sublayer in the form of truncated Taylor expansions in the modified dimensionless layer height. The pro-posed approach is of practical interest for processing the results of field observations. The one‑parameter model, validated through comparison with available experimental data, shows that the proposed piecewise‑linear approximation is accurate throughout the entire convective ASL and demonstrates high universality.