Assimilation of Accumulated Precipitation Data

Reference: Precipitation Data Assimilation in the WRFDA Users' Guide

Source code

Get the pre-compiled code, if you have not done so.

WRFDA/var/build/da_wrfvar.exe is the executable that will be used in this practice session.

Working directory

We recommend you create a new working directory for this exercise:

mkdir /classroom/users/$USER/DA/rainfall
cd /classroom/users/$USER/DA/rainfall

Input data

The test data for this rainfall tutorial case can be found in /classroom/wrfhelp/DATA/WRFDA/Rainfall This test case is the same domain as the 3dvar test case (continental US, February 5, 2008), but at a lower resolution due to the constraints of the classroom computers ln -fs /classroom/wrfhelp/DATA/WRFDA/Rainfall/ob/ob.rain.2008020518.06h ob07.rain ln -fs /classroom/wrfhelp/DATA/WRFDA/Rainfall/rc/wrfinput_d01 ./fg ln -fs /classroom/wrfhelp/DATA/WRFDA/Rainfall/rc/wrfinput_d01 . ln -fs /classroom/wrfhelp/DATA/WRFDA/Rainfall/rc/wrfbdy_d01 . ln -fs /classroom/wrfhelp/DATA/WRFDA/Rainfall/be/be.dat . These are the observation, first guess, boundary, and background error files, respectively. It is necessary to link a few more files for a 4D-VAR precipitation run

ln -fs /classroom/users/${USER}/DA/WRFDA/run/RRTM_DATA_DBL ./RRTM_DATA
ln -fs /classroom/users/${USER}/DA/WRFDA/run/*.TBL .

Edit namelists

A very basic namelist.input file for running this tutorial case is available at /classroom/wrfhelp/DATA/WRFDA/Rainfall/namelist.input.

cp /classroom/wrfhelp/DATA/WRFDA/Rainfall/namelist.input .
vi namelist.input

Pay special attention to the following namelist variables, making sure they are set to these values:

&wrfvar1
var4d=true, Remember: precipitation DA only works with 4DVAR.
var4d_lbc=false,
var4d_bin=3600,
var4d_bin_rain=21600,
...
/
...
&wrfvar4
use_rainobs=true,
thin_rainobs=true,
thin_mesh_conv=20.,
/

Run 4D-VAR with Accumulated Rainfall Observations

mpirun -np 6 /classroom/users/${USER}/DA/WRFDA/var/build/da_wrfvar.exe

Note! In the provided namelist, we haven't set a small limit for ntmax (maximum number of iterations of the cost function minimization) like we did for some other exercises. Therefore, on the classroom computers this case will take some time, probably more than 10 minutes. If you would rather move on quickly and do not care about reaching the full minimization, set ntmax=5; this will still not be instantaneous, but will only take a minute or two.