Single observation impact experiment

General

The results of single observation impact experiment provide useful information of the observation operator and error statistics. Among others, it is a useful tool for diagnosing background error statistics. The procedure described below is the recommended one and it has been tested on HARMONIE harmonie-43h21. The example below with the new system is for a AROME domain covering Denmark (DOMAIN=DKCOEXP). Three TEMP observation types have been implemented in scr/Create_singe_obs as deviations to the background:

• A temperature increase of 1K
• A wind speed increase of 1 m/s
• A specific humidity reduction to 90% of the background.

Illustrative example of single observation impact experiment on ECMWF

1. Folow instructions to create an experiment e.g. at ECMWF.

2. Edit ecf/config_exp.h as follows:

   • set ANASURF=none,
   • set SINGLEOBS=yes,
   • set LSMIXBC=no,

3. Edit scr/include.ass as follows:

   • set USEOBSOUL=1,

4. Do a checkout of bator_lectures_mod.F90

   ./Harmonie co src/odb/pandor/module/bator_lectures_mod.F90

   and change lines 296-300 to use the free format

   296 READ (NULOBI,*,iostat=iret) &
   297           & ival1,iotp,ioch,zval1,zval2,cval,ival2,ival3,zval3,inbw,ival1,ival1,&
   298           & (ztval(:),j=1,inbw)
   299 
   300   !READ(NULOBI,*,iostat=iret) (ztval(:),j=1,inbw)

5. In Env_submit set

   34 if ( $job eq 'Forecast' or $job eq 'Dfi' or $job eq 'Listen2file' ) {
   35  $nprocx=16;
   36  $nprocy=31;
   37 } else {
   38  $nprocx=1;
   39  $nprocy=1;
   40 }

6. Launch the single observation impact experiment:

   ./Harmonie start DTG=2012061003 DTGEND=2012061006

7. The resulting analysis file be found as $SCRATCH/hm_home/<exp>/archive/2012/06/10/06/MXMIN1999+0000. You can now diagnose the 3D-VAR analysis increments of the sinob-experiment taking the difference between the analysis MXMIN1999+0000 (analysis) and the first guess, $SCRATCH/hm_home/<exp>/archive/2012/06/10/03/ICMSHHARM+0003. Plot horizontal and vertical cross-sections of temperature and other variables using your favorite software (EpyGram for example).

Note that you can change position of observation, observation error, variable to be observed etc. Investigate these options by taking a closer look at the script Create_single_obs.

Read more about radiance single observation experiments here. In ec:/smx/sinob_wiki_ml you will also find OBSOUL_amsua7, a file for generating a satellati radiance amsu a channel 7 single observation impact experiment.