Comparisons of predicted bore evolutions by the Benjamin-Davis-Ono and Navier-Stokes equations for idealized mesopause thermal ducts

摘要

Numerical simulations are performed employing two numerical models to contrast nonlinear bore evolutions predicted by the Benjamin-Davis-Ono (BDO) equation with evolutions described by the Navier-Stokes (NS) equations. The first model is a simple one-dimensional solver of the BDO equation; the second describes the nonlinear two-dimensional dynamics of the NS equations. Both utilize the Boussinesq approximation. Owing to their simpler, horizontally isotropic nature, only isolated thermal ducts are considered in this study. Simulations assume an initial long-wave perturbation and address the influences of perturbation amplitude and wavelength, viscosity, and nonzero background stability on the resulting evolutions. Results indicate that the BDO equation provides reasonable predictions of bore character and evolution for conditions that satisfy its underlying assumptions. BDO predictions fail to describe bore character and evolution in cases where either the initial perturbations or the thermal environment differs significantly from BDO assumptions. Predictions employing the NS equations will thus provide more realistic guidance in the interpretation and understanding of bores observed in the mesopause region for general environments.