Regarding defaults value change of rhminl 0.8975 to 0.9900

[rajkmsaini]

Dear Friends,

I am using cesm1_2_2 and am new to use this software. It's a very big task for me to understand this and am going through it step by step. I am working on a problem where I need to define the user to define the value of relative humidity like rhminl = 0.800, 0.88 and 0.99 .

e.g.
I want to change the default value of rhminl 0.8975 to 0.9900.

I am not able to define because I am new to this software use. If you help me regarding this so It a great help me step by step to understand this.

Thank you in advance.

 

[mlevy]

cldfrc_rhminl is a CAM namelist variable, so its value is set in atm_in. From your case directory, you can look at CaseDocs/atm_in to see what namelist variables are set to but DO NOT EDIT THAT FILE. That file is auto-generated, and any changes you make will be overwritten. To change the value from 0.8975 to 0.99, add the line cldfrc_rhminl = 0.99 to the file user_nl_cam (also in your case directory). You can then run ./preview_namelists and see the updated value in CaseDocs/atm_in

 

[hannay]

I want to add that these are very extreme values. I am not sure the model will run for long.

 

[cacraig]

I would also like to point out that if you have not done so yet, I encourage you to read the CAM User's Guide. For the CESM1_2_2 version it is at:
User's Guide to the Community Atmosphere Model CAM-5.3.

In the User's Guide, it goes into detail on how to run and modify the model. There are a couple of sections in it which discuss the namelist and how to modify settings. There is also a link in that document which takes you to the complete list of namelist variables and their definitions.

 

[rajkmsaini]

cldfrc_rhminl is a CAM namelist variable, so its value is set in atm_in. From your case directory, you can look at CaseDocs/atm_in to see what namelist variables are set to but DO NOT EDIT THAT FILE. That file is auto-generated, and any changes you make will be overwritten. To change the value from 0.8975 to 0.99, add the line cldfrc_rhminl = 0.99 to the file user_nl_cam (also in your case directory). You can then run ./preview_namelists and see the updated value in CaseDocs/atm_in

is there the only way?

This one I have done. I am looking at how can be changed with the default value in the .xml file.

Please comment on it.

Thank you in advance.

 

[cacraig]

If you really want to get into the expert details of the namelist, they are documented for CESM1_2_2 in Appendix B in the CAM-5.3 User's Guide:

Appendix B. The build-namelist utility

This is really for Expert Users, and not something that we encourage beginner and even intermediate users to get into.

If you explain your reasoning for not wanting to set the value in a user_nl_cam file, we can perhaps advise you further.

 

[rajkmsaini]

If you really want to get into the expert details of the namelist, they are documented for CESM1_2_2 in Appendix B in the CAM-5.3 User's Guide:

Appendix B. The build-namelist utility

This is really for Expert Users, and not something that we encourage beginner and even intermediate users to get into.

If you explain your reasoning for not wanting to set the value in a user_nl_cam file, we can perhaps advise you further.

Thanks for the reply.

I know user_nl_cam file, it will do a great job there is no doubt about it.

There is one reason, my mentor wants to do it by XML change that the only reason.

if you could help with this. It's great input from your side.

 

[rajkmsaini]

I want to add that these are very extreme values. I am not sure the model will run for long.

I want to test the sensitivity analysis. That's it.

Thanks for comment on it .

 

[cacraig]

You can create a "use_case" that you would then use for your sensitivity studies. A use_case is basically a custom namelist which is used whenever it is specified. You can create a separate named use_case for each value that you test and it will serve as documentation for the run that you made. Sample use_case files can be seen at: $CAM_ROOT/models/atm/cam/bld/namelist_files/use_cases

If you are adamant that you want to change the namelist_defaults.xml file , which again we do not recommend at all, you may do so. Be aware that this is VERY dangerous as it will have implications on all future runs using your code base. It is very easy to forget that you have changed a value in this file and months from now spend considerable time hunting down a bug due to it.

 

[rajkmsaini]

You can create a "use_case" that you would then use for your sensitivity studies. A use_case is basically a custom namelist which is used whenever it is specified. You can create a separate named use_case for each value that you test and it will serve as documentation for the run that you made. Sample use_case files can be seen at: $CAM_ROOT/models/atm/cam/bld/namelist_files/use_cases

If you are adamant that you want to change the namelist_defaults.xml file , which again we do not recommend at all, you may do so. Be aware that this is VERY dangerous as it will have implications on all future runs using your code base. It is very easy to forget that you have changed a value in this file and months from now spend considerable time hunting down a bug due to it.

Thanks for your suggestion.