Customizing pyCMBS benchmarking environment

The model benchmarking framework can be easily customized and adapted to the user needs. In the following, we will cover the following topics:

• How to add new variables for an already existing model output format?
• How to add new observational datasets?
• How to integrate new variables in the analysis?
• How to use already existing external scripts together with the pyCMBS environment?
• How to add a new model format?

How to add new variables for an already existing model output format?

A particular model output format is represented in pyCMBS by its own class. For an already existing model class, one needs to implement a reader for each variable. In principle, this is just a small subroutine that has the logic implemented how to properly read the data. Typically this requires:

• generation of filename dependent on e.g. experiment ID
• reading data into a Data object

To implement a new variable reader, there are several ways. You can either implement one routine per variable or make use of generic I/O routines (see routine get_model_data_generic in modely.py)

How to add new observational datasets?

The integration of new observational datasets is very simple as long as the datasets you use follow some standard conventions:

• datasets are in netCDF format
• optional: datasets have metadata attributes in the netCDF file. pyCMBS is making automatically use of CF conventions like netCDF attributes like scale_factor, add_offset, _FillValue, units. In case these attributes are provided, they are automatically used
• lat/lon coordinates are provided either as vectors (for simple lat/lon projections) or as 2D fields (a (lat, lon) tuple for each grid cell).
• observations are stored in a single file (all timesteps included)

Steps to integrate a new observational dataset into pyCMBS are as follows:

• decide for the variable the observational dataset belongs to –> variable name; you can look in the configuration file (.cfg) to get the currently supported variable names
• modify the corresponding INI file

• let’s say, that you have chosen sis (surface solar irradiance) as the variable and you have a new surface radiation dataset. Then the corresponding INI file would be sis.ini. The INI files can be found in the configuration folder.

• You can however also generate an own, new configuration folder, by simply typing pycmbs.py init in a fresh directory

• The content of the INI file is self explanatory. You have a global section which specifies how the analysis for this particular variable shall be made (e.g. which diagnostics and plots shall be generated). Below, you have for each observational dataset a section which specifies the details for each observation. Such a section looks e.g. like the following:

  [CERES]
  obs_file = #get_data_pool_directory() + 'data_sources/CERES/EBAF/ED_26r_SFC/DATA/CERES_EBAF-Surface__Ed2.6r__sfc_sw_down_all_mon__1x1__200003-201002.nc'#
  obs_var  = sfc_sw_down_all_mon
  scale_data = 1.
  gleckler_position = 2
  add_to_report = True
  valid_mask = global
  

The different entries have the following meaning

[id] : str

id of observational dataset. Will be used e.g also as labels for plots

obs_file : str

path to the netCDF file with the observations here you can either specify an absolute path or you can out a python code snipped between two hashes ‘#’. The latter approach is usefull, when you have some function that directs to a particular directory, like in the example given. Otherwise, the easiest way is to just put the absolute path to the netCDF file.

obs_var : str

specifies the name of the variable in the netCDF file

scale_data : float

a multiplicative scaling factor that is applied to the data when it is read

gleckler_position : int

[1...4]; This number specifies, where the observational dataset will be placed in the portraet diagram (???)

add_to_report : bool

[True,False], specifies if the observational dataset should be included in the report or not. This allows to have a lot of configurations in the INI file, but use only a few of them.

valid_mask : str

[land,ocean,global], specifies which area(s) are supposed to contain valid data. Other regions are automatically masked. Thus if you specify e.g. land, then the ocean will be masked. It is important, that you use a

Adding a new observation is as simple as copy/paste an already existing section and modify the entries like you need it. That’s it ... well at least on a technicla point. If everything is working properly and if the diagnostics you want to apply for this observational dataset are usefull is a different question.

Recepies for handling problems

In 80% of the cases, pyCMBS will handle your new data smoothly. However, it might happen that your file(s) are different from the files pyCMBS was tested so far with. For these cases the following steps might help to solve your problem:

Is the file o.k?

• Have a look at the file with other tools like e.g. ncview or panoply
• make also an “ncdump -h” to check the metadata of the file

Can cdo’s work with the file?

The preprocessing capabilities of pyCMBS largely rely on the usage of the climate data operators (cdo). If the cdo’s can not work with your file, then pyCMBS will most likely have also problems.

• check if cdo’s can in general read the file: cdo sinfo <filename>
• check if grid of the file is recognized by trying to remap the file manually using cdo remapcon,t63grid <infile> nothing.nc

If one of the two tests above fail, then your file is missing some essential metadata or has a strange grid or grid description that is not automatically recognized. In these cases, it would be best, if you try to figure out, why the cdo’s are not capable to work with your dataset. Try to pose your question to the cdo’s help forum (don’t forget to provide details about your file; e.g. by sending the results of ncdump -h)

How to integrate new variables in the analysis?

To add new variables in pyCMBS implies the following steps:

1. Define I/O routine: Implement for each model class that shall support the new variable a routine that allows to read the data. Let’s say you have a variable sis, then you would need e.g. to implement a routine get_sis() for the CMIP5 model class. Note that there is already a routine which can be used for generic I/O.

2. Register I/O routine: After you have implemented the routine to read the data, you need to let the program know about it. All data is read using a routine called get_data(). This routine gets the information which subroutines to call from details provided in a configuration file. The configuration file is found in:

./configuration/model_data_routines.json

The file is a simple JSON dictionary. Make yourself a bit familar with the structure and it should not be a problem to implement your new routine there.

3. Analysis script: Now you have the analysis script that can be used to read the data. However, you still need to tell pyCMBS how to make use of this new information. This you do by implementing an analysis routine in analysis.py. For most variables supported so far, this analysis routine is just a wrapper which is calling a very generic analysis routine that basically does everything you tell it to do. What to do is specified in the INI files for each variable. Note however, that you are free to do what you want and you can implement a new analysis routine which is doing right the thing you want it to do.

4. Last step is to tell pyCMBS that the analysis script you implemented is existing. This is again done, by simply registering it in the following file:

./configuration/analysis_scripts.json

How to add a new model format?

Each model is represented by its own class which is herited from the Model class. Each model object/class needs to support reading of the variables that should be used for the analysis. Please look at the current code in models.py to see how the actual implementation can look like. Important is a coherent support of the routines which are importing data from files for a model specific file format.