CGD's Dr. Akira Kasahara

Kasahara, A., 2007: Initial-value approach to study the inertio-gravity waves without the "traditional Approximation". Journal of Computational Physics, 225, 2175-2197.

Abstract

The dynamical framework for the current weather prediction and climate models are generally based on the nonhydrostatic primitive equations with some major approximations. Those approximations seem to lead to the errors in the dynamical part on the order of few percent which is on the same order of errors expected from the physical processes. Since more detailed physical processes, such as the influence of aerosols, will be included in the next-generation earth system models, it is desirable to reduce the errors in the dynamical part by eliminate major dynamical approximations.

This article will contribute to understanding the nature of one of the major model assumptions, called the "traditional approximation" which neglects the role of horizontal component of Coriolis force in the models.

An initial-value problem is formulated with linear Boussinesq equations to study the inertio-gravity waves without the traditional approximation. Motions are assumed to be horizontally periodic, but bounded vertically at the top and bottom. The evolution of the vertical structure of wave motions is calculated from given initial conditions with or without forcing/dissipation under a variable thermal buoyancy condition in height.

This program is intended to use as a simple numerical laboratory to study the time-evolution of inertio-gravity waves. Examples show for (1) the free oscillations using the normal mode solutions as initial conditions, and (2) the forced oscillations as a simulation of near-inertial currents in the oceans generated by atmospheric storms. An emphasis is made to asses the role of the horizontal component of the earth's rotation which has been traditionally neglected in the study of inertio-gravity waves.

Support: Private fund and National Science Foundation.