Implicit Time Stepping and Preconditioning for Atmospheric Dynamics in the Community Atmosphere Model

Abstract:

High resolution, long-term climate simulations are essential to understanding regional climate variation on the decade scale. Implicit time stepping methods provide a means to maintain accuracy while taking time steps commensurate with the physical processes of interest. We present results utilizing a second order implicit time stepping method in the hydrostatic spectral element dynamical core of the Community Atmosphere Model (CAM-SE). Because this method can take much larger time steps and remain stable with measured accuracy, efficiency gains for some test cases and model configurations are realized, depending on the time scales of interest. The growth of linear iterations in the Newton-Krylov method for solving the nonlinear residual equation highlights the need for scalable preconditioning. We discuss the development of a block preconditioner for the hydrostatic equations to reduce the cost of ancillary linear system solves within each time step to improve solver efficiency and scalability.