We have carried previous studies using a simple two-layer model of the atmosphere with a fairly complete surface energy budget. This allowed the dynamical analysis to be carried out on a coupled set of four ordinary differential equations. The present paper extends this work by examining additional bifurcation parameters and, more importantly, the analysis of a set of partial differential equations with full vertical dependence. Simple mathematical representations of classical problems in dynamical analysis often exhibit interesting behavior, such as multiple solutions, that is not retained in the behavior of more complete representations. In the present case the S-shaped bifurcation diagram remains with only slight variations from the two-layer model. For the parameter space in the fold-back region, the evolution of the boundary layer may be dramatically affected by the initial conditions at sunset. An eigenvalue analysis carried out to determine whether the system might support pure limit-cycle behavior showed that purely complex eigenvalues are not found. Thus, any cyclic behavior is likely to be transient.
In weather forecast and general circulation models the behavior of the atmospheric boundary layer especially the nocturnal boundary layer can be critically dependent on the magnitude of the effective model grid-scale surface heat capacity. Yet, this model parameter is uncertain both in its value and in its conceptual meaning for a model grid in heterogeneous conditions. Current methods for estimating the grid-scale heat capacity involve the areal/volume weighting of heat capacity (resistance) of various, often ill-defined, components. A bifurcation analysis with heat capacity as the bifurcation parameter shows that there are multiple solution regimes. Since heat capacity is a multiplying factor of the flux terms in the surface energy equations, it would appear that the model solutions would be highly dependent on this parameter. The bifurcation analysis shows that there are two regimes for sensitivity. For small values of heat capacity the system is highly sensitive to change in heat capacity. However, for large values of heat capacity the system shows little sensitivity to this parameter. This has important implications for numerical techniques for solving the surface energy budget. In most models only a very low order ODE solver is used for the surface temperature equation. This choice is probably rooted in the fact that since the flux terms are assumed to be uncertain a higher order scheme is not needed. However, the nonlinear analysis and numerical time dependent simulations show that in the small heat capacity regime numerical stability problems can exist.
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