=============
MPAS Overview
=============

The Model for Prediction Across Scales - Atmosphere (MPAS-A) is a non-hydrostatic atmosphere model that is part of a family of Earth-system component models collectively known as MPAS. All MPAS models have in common their use of centroidal Voronoi tessellations for their horizontal meshes, which has motivated the development of a common software framework that provides a high-level driver program and infrastructure for providing parallel execution, input and output, and other software infrastructure.

|

|

Features
========

**Important features of MPAS-A include:**

*   Fully-compressible, non-hydrostatic dynamics
*   Split-explicit Runge-Kutta time integration
*   Exact conservation of dry-air mass and scalar mass
*   Positive-definite and monotonic transport options
*   Generalized terrain-following height coordinate
*   Support for unstructured variable-resolution (horizontal) mesh integrations for the sphere and Cartesian planes
*   Support for global and limited-area simulation domains

|

|

**MPAS-A includes support for the following parameterizations of physical processes.** |br|
*These are taken from the* `Weather Research and Forecasting (WRF) Model <https://www.mmm.ucar.edu/models/wrf>`_.
    
*   Radiation: CAM and RRTMG long-wave and short-wave radiation schemes
*   Land-surface: NOAH land-surface model
*   Surface-layer: Monin-Obukhov and MYNN
*   Boundary-layer: YSU and MYNN PBL schemes
*   Convection: Kain-Fritsch Tiedtke, New Tiedtke, and Grell-Freitas convection parameterizations
*   Cloud microphysics: WSM6, Kessler, and Thompson schemes

|

|

|

.. _Model Components:

Model Components
================

MPAS-A is comprised of the following two primary components:

#.   **Initialization component**
       Generates initial conditions for the atmospheric and land-surface state, updates files for sea-surface temperature and sea ice, and lateral boundary conditions

#.   **Model**
       Includes atmospheric dynamics and physics

Both components are built as cores within the MPAS software framework and make use of the same driver program and software infrastructure. However, each component is compiled as a separate executable.

|

.. figure:: ../../images/ug/mpas-a_components.png
   :width: 250px
   :height: 250px
   :align: center

   *The initialization and model components of MPAS-A are built as separate \*cores\* within the MPAS framework.*

|

*   `See the Quick Start Guide <./quick_start.html>`_ for a succinct description of building and running MPAS-A. 
*   `See Building MPAS <./building_mpas.html>`_ for detailed instructions for building these components.
*   `See Running MPAS <./running.html>`_ for basic steps to create initial conditions and run the MPAS-A model.

|

|

|

|

|

.. rst-class:: horizbuttons-next-m

* `Next: Quick Start Guide -> <./quick_start.html>`_

|