Das Atmosphärische Modell (DAM)

Model Description

David M. Romps


Overview

Das Atmosphärische Modell, also known as DAM, is a three-dimensional, finite-volume, fully compressible, nonhydrostatic, cloud-resolving model with adaptive time stepping and MPI parallelization. Work on DAM began in April 2007 and DAM was first described in the following paper:

David M. Romps. The dry-entropy budget of a moist atmosphere”. Journal of the Atmospheric Sciences. 65. 3779–3799. 2008.

Equations

The prognostic variables in DAM are the momenta, virtual potential temperature, density (of moist air), and the mass fractions for six classes of water. A detailed description of the governing equations can be found here.

Grid

DAM uses the Arakawa C-type grid with uniform horizontal spacing and variable vertical spacing using geometric height as the vertical coordinate. The upper and lower boundary conditions are that of a no-slip, rigid lid and the horizontal domain is doubly periodic. There are eight types of grid points depending on whether the location of the grid point in each of the three dimensions is a scalar (denoted by an s) or interface (denoted by an i) level. The eight types of grid points are denoted by sss, iss, sis, ssi, iis, isi, sii, and iii.

Figure 1. An x-z slice of the Arakawa C-type grid for a single subdomain.

An x-z slice of the Arakawa C-type grid for a single subdomain.


For example, the grid point labeled as the location of pressure p is an sss grid point. The grid points at the locations of the u velocities are iss grid points. The grid points at the locations of the w velocities are ssi grid points. The corners of any of the solid-line boxes in this figure are isi grid points.

Integration

DAM uses a split-explicit time stepping approach to acoustic modes and gravity waves. The terms in the governing equations that are responsible for sound waves and gravity waves are integrated with a small time step (the acoustic loop) while the other terms are integrated with a larger time step (the Runge-Kutta loop). A detailed description of the integration method can be found here.

Advection

Quantities are transported around the grid with a conservative flux-based finite-volume scheme. Quantities are interpolated from scalar grid points to interface grid points (and vice versa) using a third-order upwind stencil. Those interpolated values are then refined to ensure monotonicity using the multidimensional flux limiter of Thuburn (1996).

Microphysics

The microphysics scheme is that of Lin, Farley, and Orville (1983), which was further modified by Lord, Willoughby, and Piotrowicz, and then further modified by Krueger et. al. (1995). It is a six-class bulk scheme comprising water, cloud liquid, rain, cloud ice, snow, and graupel.

Radiation

For shortwave and longwave radiation, DAM uses the Rapid Radiative Transfer Model of Clough, et. al. (2005) and Iacono et. al. (2008).