EMS WRF

2014-03-06

EMS-WRF for Coimbatore region using four domains
Five simple steps required for the execution of EMS (Environmental modeling system) WRF.

After the successful installation of EMS follow these steps,

Step 1: Create a computational domain with the Domain Wizard(DW) GUI

Start the DW by executing the command “dwiz” in the terminal.
DW window should appear and gives an option to select from creating a new domain or modifying an existing Domain. The current run directory also is shown in this window.
Select “Create a new Domain” and then the “Continue” button.
“Name your domain challenge window” should appear and give the name to Domain. Name of Domain should be in lower case characters without any spaces. Example: cbrwrf. Which creates a new directory cbrwrf underneath wrfems/runs/cbrwrf.
Click on the “Continue” button to move on to the “Horizontal Editor” window.
The Horizontal Editor window allows defining a model domain by drawing a bounding box on a map. Edit the “Centerpoint Lon = 77.03 “and “Centerpoint Lat =11.03 “in Projection, Options to get specific region of interest( Coimbatore).
On the right side of the window, in Domain menu map section allows to change the “Scale = 12.5%” and “Center = Over 180 degrees longitude”. In Projection Options (degrees) change the “Type = Lambert Conformal”. The grid points in X & Y directions and resolution of geographic data in Grid options can be changed.
Click on “Update Map,” this will create a primary domain of region.
Nested domain configuration by selecting “Nests” menu gives the option to create new nested domains or edit/delete existing ones.
To create a new sub-domain, click on the “New” button to bring up the “New Nest” configuration window. Here Nest properties section allows for editing the parent ID, Grid spacing ratio to parent, Geographic data resolution and Nest coordinates defines the coordinates of particular Domain.
Created four domains to stimulate Coimbatore region with 1KM resolution.
Click on the “Next” button to run the Localization in Run Preprocessors window. Localization serves to extract the terrestrial data over the area covered by the Domain (s) from the large global files at the resolution(s) that specified during domain creation.
Click on “Localize Domain.”
After successful execution geogrid created four output files such as geo.em.d01.nc , geo.em.d02.nc , geo.em.d03.nc , geo.em.d04.nc. These files will reside in wrfems/runs/cbrwrf/static.
Click on the “Next “button and select each Domain to visualize the outputs by clicking on “view in panoply”. Gives dataset window and double click on any dataset to display.
Click “Exit” to finish the work.

Step 2: Prepare to run a simulation.

A new domain “cbrwrf” is created and placed in the directory wrfems/runs/cbrwrf. From this directory, Simulation happens.
The EMS default configuration should be sufficient for running simulations. However, sometimes it will change so two configuration files can review to make sure everything is correct.
In the “conf/emsrun/runncpus.conf” configuration file, make sure that the number of CPUs correct for the computer. Check the following parameters :
```
REAL_NODECPUS = local:3
WRFM_NODECPUS = local:3 
```
Where 3 represents the number of processors on the system.
The other file that might want to examine is “conf/emsrun/runphysics.conf”, which contains all the model physics settings for Simulation. If your grid spacing is less than 8 KM then change the parameter CUPHYSICS = 1,0 to CUPHYSICS = 0,0 or CU_PHYSICS = 5,0

Step 3 : Processing your Initialization data

This step assumes that have an internet connection so that the initialization data can be accessed. By running the following command in Domain (Directory: wrfems/runs/cbrwrf):
```
% ems_prep --dset gfs --length 24 
```
If bandwidth is limited, then try running:
```
% ems_prep --dset gfsptiles --length 24 
```
Running either command causes the ems_prep routine to download and process the first 24 hours of forecast files from the most recent Global Forecast System (GFS) operational model run. These files will serve to provide initial and boundary condition data for a 24-hour simulation (“–length 24”).

For nested domains try the following command

% ems_prep –dset gfsptiles –domains 2,3,4 (for 3 nested domains) or
% ems_prep –dset gfsptiles –domains 4  (this will automatically activate 2,3 domains too)

Domain 1 is the parent of all domains and so by default included.
Check wrfems/runs/cbrwrf/wpsprd , where all the WRF intermediate files located.

Step 4: Running the Simulation

Change directory to wrfems/runs/cbrwrf , and run the following command
```
% ems_run
```
For nested domains, run the command
```
% ems_run –domains 2,3,4
```
Output files will reside in wrfems/runs/cbrwrf/wrfprd

Step 5: Processing the model output files

WRF output files are created after successful Simulation. These data is in netCDF format and viewed using ncview command. So try the command
```
% ncview <netCDF file>, ex
% ncview wrfbdy_d01
```