Resolved Scales and Nonlinear Interactions in Limited-Area Models

Abstract

A procedure for identifying the resolved scales in nested limited-area models (LAMs) and for computing the nonlinear interactions between these scales is sketched in this paper. The spectral perspective is adopted and implemented semiempirically by analogy with global and r-periodic sectorial models. The analysis indicates that resolved scales are limited in LAMs and sectorial models compared to global models of similar resolution, and that nonlinear interactions may be treated less accurately in LAMs than in global models. A further result of the analysis is the evidence of the paramount importance of nesting, which acts as a type of closure scheme required by LAMs due to their limited computational domain. The assignment of lateral boundary values (LBVs) is responsible for making LAMs nonperiodic; these LBVs include scales exceeding the size of the LAM's domain and several other shorter scales that are nonperiodic on the limited computational domain.