==================
Restart Simulation
==================

|vspace|

The **restart** option allows users to extend a run when the entire simulation cannot be done at once (e.g., not enough wall-clock time). This creates a continuous run from two or more shorter runs.

To do this, run an initial WRF simulation. *restart_interval* in *namelist.input* must be set to the desired interval for restart output files (*wrfrst_d0\**). The restart simulation can start from the time stamp from one of the *wrfrst\** files.

|vspace|

.. note::
   Restart runs aid troubleshooting. If a simulation crashes, use restart files to resume just before the crash for easier debugging with print statements, avoiding a full simulation.

|vspace|

.. figure:: ./images/run_cases1_gray.png
   :align: center
   :width: 60%

|

|

Set-up WRF
==========

**If you successfully ran the Single Domain case, you should have restart files to use for this case.**

#.   Move to the **/glade/scratch/$USER/practice_exercises/wrf/test/em_real/** directory.

     |vspace|

#.   Edit **namelist.input**. The only values that need to be changed are in the *&time_control* record, and are highlighted below:

     |vspace|
     
     .. code-block::
        :emphasize-lines: 1,6,14-15

        run_hours = 12,
        run_minutes = 0,
        start_year = 2023,
        start_month = 03,
        start_day = 31,
        start_hour = 12,
        end_year = 2023,
        end_month = 04,
        end_day = 01,
        end_hour = 00,
        interval_seconds = 21600
        history_interval = 180,
        frames_per_outfile = 1,
        restart = .true.,
        restart_interval = 72000,

     |vspace|

#.   Make sure the original *wrfout_d0\** files are saved elsewhere (e.g., inside the *single_domain/* directory you created to store the output), so they do not get overwritten.

     |vspace|

#.   Restarts require the *wrfbdy_d01* file and the *wrfrst\** file at the restart initial time to be in the running directory. If you stored those files in a *single_domain/* directory, copy them back into the running directory.
     
     .. code-block::
        :class: copyable
        
        cp single_domain/wrfbdy_d01 .
        cp single_domain/wrfrst_d01_2023-03-31_12:00:00 .

#.   Restarts don't require a re-run of real.exe, as the *wrfrst\** file contains initial conditions (and serves as the *wrfinput_d01* file). Submit the *runwrf.sh* script to the queue.

     .. code-block::
        :class: copyable

        qsub runwrf.sh

     |vspace|

     Use the *qstat* command (as in the `Single Domain Run <./single_domain.html>`_ case) to check the status, and view *rsl.out.0000* for the "success" message. If successful, the following new history files should be available:

     .. container:: row m-0 p-0

        .. container:: col-md-6 pl-0 pr-3 py-3 m-0

           .. container:: card-blockquote

              wrfout_d01_2023-03-31_15:00:00 |br|
              wrfout_d01_2023-03-31_18:00:00 |br|
              wrfout_d01_2023-03-31_21:00:00 |br|
              wrfout_d01_2023-04-01_00:00:00 |br|

|vspace|

.. note::
   A *wrfout\** file is not output for the start time of 12 UTC. This is a safety feature to prevent overwriting the previously created file. To output a file for the initial time, add the following line anywhere in the *&time_control* namelist record.

   .. code-block::

      write_hist_at_0h_rst = .true.

|

|

Check your output
=================

*   View the log files (*rsl.out\**).
*   Tail the *rsl.out.0000* file and look for **SUCCESS COMPLETE WRF**.
*   Use the ``ncdump`` command to see output times available in the wrf history file.
*   Use the netCDF data browser 'ncview' to examine your wrf output file.
*   `Generate graphics <./graphics.html>`_ with one of the supplied packages.

|

|

Return to the Practice Exercise home to page to run another exercise. 

.. rst-class:: horizbuttons-primary-m

* `Return to Practice Exercises <./practices.html>`_

.. toctree::
   :maxdepth: 4
   :hidden:

|vspace|

|vspace|

|vspace|

|vspace|