HR: 11:30h
AN: A32A-07    [Abstracts]
TI: A New 3-D Potential-Enstrophy-Conserving, Compressible, Nonhydrostatic Model for Weather and Climate Simulation on All Scales and Its Application to San Francisco
AU: * Ketefian, G S
EM: gsk@stanford.edu
AF: Gerard Ketefian, Dept. of Civil & Environmental Eng. Terman Eng. Ctr. Rm. M-13 Stanford University, Stanford, CA 94305 United States
AU: Jacobson, M Z
EM: jacobson@stanford.edu
AF: Gerard Ketefian, Dept. of Civil & Environmental Eng. Terman Eng. Ctr. Rm. M-13 Stanford University, Stanford, CA 94305 United States
AB: We present a unique atmospheric dynamics model useful from the microscale to the global scale and discuss its application to flow through San Francisco. The model, PECCAN (Potential Enstrophy Conserving Compressible Atmospheric Nonhydrostatic), solves the governing equations for a fully compressible 3-D nonhydrostatic atmosphere. The model is unique because it conserves the domain integrals of all of the following quantities simultaneously: (1) potential enstrophy in the limit of barotropic flow in 2-D, (2) total energy (kinetic plus potential plus internal energy) for frictionless flow in 3-D, (3) mass in 3-D, and (4) potential enthalpy (the product of specific heat, density, and potential temperature) for adiabatic flow in 3-D. A new feature of this model is that it generalizes the potential enstrophy and energy conserving numerical scheme of Arakawa and Lamb (1981) for the 2-D shallow water equations to discretize the nonlinear terms in the governing momentum equations of 3-D atmospheric flow. Various authors have demonstrated that, at least for 2-D shallow water flow, using a numerical scheme that maintains the various global conservation properties of the governing equations, especially that of potential enstrophy (PE), leads to the correct transfer of energy among scales in the model and eliminates spurious numerical sources of momentum and energy. Arakawa and Lamb (1981) have also shown that a PE-conserving numerical scheme for 2-D shallow water flow converges to the correct solution on a significantly coarser grid than does a non-PE-conserving scheme. PECCAN is written in general orthogonal curvilinear coordinates. Thus, the model simulates flows in Cartesian, cylindrical, spherical, and Lambert (polar stereographic and Mercator) coordinate systems, with stretched coordinates in any spatial direction. Stretched coordinates allow the model to cover most of the globe with a coarse horizontal grid while covering one or more regions of interest with a much finer grid. This approach eliminates the need for the use of limited-area boundary conditions. In the vertical, the model uses the altitude coordinate, although the numerical scheme can be generalized to the sigma coordinate. To advance the equations forward in time, the model uses any one of several explicit time integration schemes. These include the leapfrog, third and fourth order Runge-Kutta, second order Adams-Bashforth, and Heun schemes. To overcome the time step limitation due to sound waves, the model has the option of using a time-splitting technique in which the velocity divergence terms in the continuity and thermodynamic energy equations and the pressure gradient terms in the momentum equations are advanced using either a small time step explicitly or a large time step implicitly while the remaining meteorologically important terms are advanced using a long time step. Results discussed here include those from flows around buildings and through and above street canyons. In particular, we use a stretched grid that encompasses the globe at coarse resolution but focuses in on the city of San Francisco at high resolution ($<$ 20 m). Idealized flow tests and comparison with results from other authors will also be discussed. REFERENCES Arakawa, A. and Lamb, V. R. (1981). A potential exstrophy and energy conserving scheme for the shallow water equations. Mon. Wea. Rev., 109:18-36.
DE: 3329 Mesoscale meteorology
DE: 3337 Numerical modeling and data assimilation
DE: 3354 Precipitation (1854)
DE: 3319 General circulation
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting