An Initialization Method for Idealized Channel Simulations

Abstract

Abstract Idealized model simulations have long been established as valuable tools to gain insight into atmospheric phenomena by providing a simplified, easier to comprehend version of the complex atmospheric system. A specific subgroup of idealized simulations, such as baroclinic channel models, requires the initialization of the model with balanced atmospheric fields to investigate the evolution of an introduced perturbation. The quality of these simulations depends on the degree of balance of the initial state, as imbalances result in geostrophic and hydrostatic adjustment processes that potentially skew the results. In this paper, a general method to create geostrophically and hydrostatically balanced initial conditions is introduced. The major benefit of this method is the possibility to directly define a basic state wind field with the pertinent atmospheric fields being derived given appropriate boundary conditions. Application of the method is exemplified by constructing initial conditions for a baroclinic test case with WRF and analyzing a perturbed and unperturbed numerical simulation. The unperturbed simulation exhibits weak inertia–gravity wave activity and minimal adjustment of the initial state during a 5-day simulation, which confirms the high degree of initial balance provided by the initialization technique. In the perturbed simulation, baroclinic instability is initiated, resulting in a cyclogenesis event similar to previous idealized baroclinic channel simulations. The proposed method is compared with initial conditions formulated in a Boussinesq framework, illustrating the difference in imbalances and their effect on perturbation growth.