Rerun

Now that we've seen the output for Gen-Ens-Prod without any control ensemble members, let's change the run slightly by selecting one of the previous ensemble members as the control. Because the required changes will be performed in the run command, no edits will be made to the configuration file.

Run the following command. Note the change to the wildcards, additional flag, and change in output file name:

gen_ens_prod \

-ens ${METPLUS_DATA}/met_test/data/sample_fcst/2009123112/*gep[23567]/d01_2009123112_02400.grib \

-out ./GenEnsProd_APCP24_run2_ctrl.nc \

-config GenEnsProdConfig_tutorial \

-ctrl ${METPLUS_DATA}/met_test/data/sample_fcst/2009123112/arw-fer-gep1/d01_2009123112_02400.grib \

-v 2

When MET has successfully finished running, 1 new netCDF file will be in the current directory containing the same ensemble products that were available in the first run. However, the output is now changed by using one of the original ensemble members as the control member.

Take a look at the contents of the new netCDF file with ncview:

ncview GenEnsProd_APCP24_run2_ctrl.nc

You'll see as you click through the variables that the only difference between the two runs of Gen-Ens-Prod is APCP_24_A24_ENS_STDEV. The mean (APCP_24_A24_ENS_MEAN) and all of the categorical thresholds still use all 6 ensemble members. This is quickly confirmed by viewing APCP_24_A24_ENS_VLD for both, which shows 6 ensembles were used for both runs across the domain.

To better illustrate the difference in the APCP_24_A24_ENS_STDEV products, let's calculate the difference of the two fields using PCP-Combine, and plot the results using Plot-Data-Plane.

Use the following command to subtract the control standard deviation field from the full ensemble standard deviation field, saving it to the netCDF file and variable name provided:

pcp_combine -subtract \

GenEnsProd_APCP24.nc 'name="APCP_24_A24_ENS_STDEV"; level="(*,*)";' \

GenEnsProd_APCP24_run2_ctrl.nc 'name="APCP_24_A24_ENS_STDEV"; level="(*,*)";' \

Full_Ensemble_STDDEV_minus_ctrl_STDDEV.nc -name STDDEV_DIFF

Now, take the PCP-Combine output and create a plot of the results:

plot_data_plane Full_Ensemble_STDDEV_minus_ctrl_STDDEV.nc STDDEV_diff.ps \

'name="STDDEV_DIFF"; level="(*,*)";'

Finally, view the contents of the plot:

display STDDEV_diff.ps

If the differences weren't apparent before, this plot makes it very clear how using a control ensemble member can drastically change a product. As long as it's desired, the -ctrl option is a quick way to run Gen-Ens-Prod without control members for some products, while including it in others.

jopatz Thu, 01/19/2023 - 15:22