============= Model Options ============= | Beyond the basic process of running a global simulation with standard output files outlined in `Running MPAS-Atmosphere <./running.html>`_, the MPAS-Atmosphere model provides several options that can be described in terms of variations on the basic simulation workflow. In the sections that follow, major model options are described in terms of the deviation from the basic global simulation process. | | Periodic SST and Sea-ice Updates ================================ The stand-alone MPAS-Atmosphere model is not coupled to fully prognostic ocean or sea-ice models, and accordingly, the model SST and sea-ice fraction fields generally do not change over the course of a simulation. For simulations shorter than a few days, invariant SST and sea-ice fraction fields are generally not problematic. However, for longer model simulations, it is typically recommended to periodically update the SST and sea-ice fields from an external file. The surface data to be used for periodic SST and sea-ice updates could originate from any number of sources, though the most straightforward way to obtain a dataset in a usable format is to process GRIB data (e.g., GFS GRIB data) using the *ungrib* program from the WRF model's pre-processing system (WPS). See detailed instructions for `building the WPS `__ and `running the WPS `__, including the process of generating intermediate data files from GFS data. | The following steps summarize the process of generating an SST and sea-ice update file, *surface.nc*, using the *init_atmosphere_model* program: * Include surface data intermediate files in the working directory * Include a *static.nc* file in the working directory (`see Static Fields <./running.html#static-fields>`_) * If running in parallel, include a *graph.info.part.\** in the working directory (`see Graph Partitioning with METIS <./preparing_meshes.html#graph-partitioning-with-metis>`_) * Edit the *namelist.init_atmosphere* configuration file (see below) * Edit the *streams.init_atmosphere* I/O configuration file (described below) * Run *init_atmosphere_model* to create *surface.nc* | | **&nhyd_model** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_init_case = 8, must be 8 - the surface field initialization case config_start_time = '2010-10-23_00:00:00', time to begin processing surface data config_stop_time = '2010-10-30_00:00:00', time to end processing surface data | **&data_sources** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_sfc_prefix = 'SST', the prefix of the intermediate data files containing SST and sea-ice config_fg_interval = 86400, interval between intermediate files to use for SST and sea-ice | **&preproc_stages** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_static_interp = false |br| config_native_gwd_static = false |br| config_vertical_grid = false |br| config_met_interp = false |br| config_input_sst = true |br| config_frac_seaice = true, only the *input_sst* and *frac_seaice* stages should be enabled | **&decomposition** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_block_decomp_file_prefix = 'graph.info.part.', if running in parallel\, this needs to match the grid decomposition file prefix | After editing the *namelist.init_atmosphere* file, the names of the static file and the surface update file to be created, must be set in the XML I/O configuration file, *streams.init_atmosphere*. Specifically, * the *filename_template* attribute must be set to the name of the static file in the "input" stream definition, * the *filename_template* attribute must be set to name of the surface update file to be created in the "surface" stream definition. * ensure that *output_interval* is set to the interval at which the surface intermediate files are provided | | | Regional Simulation =================== Beginning in MPAS v7.0 is the capability to run simulations over regional domains on the surface of the sphere. Setting up and running a limited-area simulation requires, as a starting point, a `limited-area SCVT mesh <./preparing_meshes.html#creating-limited-area-scvt-meshes>`_ . Given a limited-area mesh, the key differences from a global simulation arethat for regional simulations: * blending the MPAS terrain field with the "first-guess" terrain data along the boundaries of the limited-area domain; * generate a set of files containing lateral boundary conditions (LBCs); and * apply LBCs during the model integration. | | Terrain Blending ---------------- Terrain blending takes place when generating the limited-area initial conditions, which are prepared as in `Vertical Grid Generation and Initial Field Interpolation `_, except that the *config_blend_bdy_terrain* option should be set to *true* in the *namelist.init_atmosphere* file. This instructs the *init_atmosphere_model* program to perform averaging of the model terrain field from the *static.nc* file with the terrain field from the atmospheric initial conditions dataset along the lateral boundaries of the mesh. | | LBC File Generation ------------------- LBC file generation requires running *init_atmosphere* one additional time, with namelist options set as described below. | **&nhyd_model** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_init_case = 9, the LBC's processing case config_start_time = '2010-10-23_00:00:00', time to begin processing LBC data config_stop_time = '2010-10-30_00:00:00', time to end processing LBC data | **&dimensions** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_nfglevels = 38, number of vertical levels in the intermediate file | **&data_sources** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_met_prefix = 'GFS', the prefix of the intermediate data files to be used for LBCs config_fg_interval = 10800, interval between intermediate files | **&decomposition** .. csv-table:: :width: 80% :widths: 40, 40 :escape: \ config_block_decomp_file_prefix = 'graph.info.part.', if running in parallel\, this needs to match the grid decomposition file prefix | When processing LBCs, * the *output_interval* for the "lbc" stream in the *streams.init_atmosphere* file must match the value of *config_fg_interval* in the *namelist.init_atmosphere* file. * the file to be read by the "input" stream must contain vertical grid information; typically, the model initial-conditions file can be used as the source for the "input" stream. Following this step, a set of netCDF files containing LBCs for the model integration are produced. | | Application of LBCs During Model Integration -------------------------------------------- To apply LBCs during the model integration, * set *config_apply_lbcs* to *true* in the model's *namelist.atmosphere* file * set the *input_interval* for the "lbc_in" stream in the *streams.atmosphere* file to match the interval at which the LBC netCDF files were produced. | | | Separate Stream for Invariant Fields ==================================== By default, the MPAS-Atmosphere model reads time-invariant fields (e.g., *latCell*, *lonCell*, *areaCell*, *zgrid*, *zz*, etc.) from the "input" and "restart" streams (for cold-start and restart runs, respectively), and it writes time-invariant fields to the "restart" stream. In the case of large ensembles, the time-invariant fields replicated in the restart files for all ensemble members can account for a substantial amount of storage. Since these time-invariant fields do not change in time or across ensemble members, only one copy of these fields needs to be stored. MPAS-Atmosphere v8.1.0 introduces a capability to omit time-invariant fields from model restart files. When the model restarts, a new "invariant" stream may be used to read time-invariant fields from a separate file, and many ensemble members can share this file. To make use of the "invariant" stream, several changes to the standard MPAS-Atmosphere workflow are needed. | | Preparing an Invariant File --------------------------- Through the use of the *init_atmosphere* model program, a file containing all required time-invariant fields must be prepared. Since the model initial conditions file (typically *init.nc*) contains time-invariant fields, the initial conditions file from any ensemble member may be used. If a file containing purely time-invariant fields is desired, run the following pre-processing stages, and then the output from the *init_atmosphere_model* program will suffice: * config_static_interp = true * config_native_gwd_static = true * config_vertical_grid = true | .. note:: These pre-processing stages do not need to be run all at once. It is possible, for example, to first produce a *static.nc* file using the first two of these pre-processing stages, and to then produce an invariant file (e.g., *invariant.nc*) by running the vertical grid generation stage using the *static.nc* file as input. | | Activating the Invariant Stream ------------------------------- When running the model itself (*atmosphere_model*), the use of the new invariant stream may be activated by defining the "invariant" immutable stream in the *streams.atmosphere* file as follows: .. code-block:: | In the definition of the "invariant" stream, *filename_template* should be set to the actual name of the invariant file. When the "invariant" stream exists in *streams.atmosphere*, the model omits all time-invariant fields from any restart files that are written. When the model restarts, all time-invariant fields are read from the "invariant" stream rather than from the "restart" stream. | | | | | .. rst-class:: horizbuttons-next-m * `Next: Visualization -> <./visualization.html>`_ |