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Abstract

We introduce a global spectral model that solves primitive equations with the use of the Hough harmonics, which are eigensolutions of the linearized rotating shallow-water equations on the sphere. This transforms the momentum and continuity prognostic equations into the set of equations for the Rossby and non-Rossby waves. The latter consist of the inertia-gravity, the Kelvin, and mixed Rossby-gravity (MRG) waves. The new model, named TIGAR - Transient Inertia-Gravity And Rossby wave dynamics, thus treats different types of waves explicitly, providing a framework to study wave-mean flow and wave-wave interactions directly in the model. Wave filtering, leading to simplified models aimed at particular dynamical regime such as that of tropical flows is straightforward and computationally efficient to implement. Numerically, high precision computation is achieved in TIGAR through the use of higher order integrating factor and exponential time-differencing schemes, which take advantage of the framework, leading to the major increase in computational efficiency and stability. In the talk, we present the model formulation, TIGAR solutions of some classical tests for dynamical cores, from barotropic steady state to barotropic and baroclinic instability tests, and compare them to the solutions of the conventional spectral model PUMA.