time step in CCM3

[a_s_vonderheydt@phys_uu_nl]

Dear CCM and CAM users,

I am using the CCM3.6.6. within Paleo-CCSM simulations with continents different from today. With some
continental geometries everything worked fine, but now I tried a new one, and then the atmosphere model
crashes at some point with the error message:

CUBYDR: Departure point out of bounds: jcen,icount,pgls= 39, 1726, 1728

which seems to have to do with the length of the time step.
I use the T31 resolution with a time step

DTIME=1800

as it should be for this resolution. The problem seems to be solved by just setting the time step to 1200
seconds as is recomended for the T42 resolution. However, then physical parametrizations also change, and I
don't know what I have to expect from that. Can I just change the time step without changing other
parameters?

It would be nice if I could get some help with that.

Best regards,

Anna

--------------------------------
Dr. Anna von der Heydt
Institute for Marine and Atmospheric Research
Utrecht University
The Netherlands

 

[pjr]

Dear CCM and CAM users,

I am using the CCM3.6.6. within Paleo-CCSM simulations with continents different from today. With some
continental geometries everything worked fine, but now I tried a new one, and then the atmosphere model
crashes at some point with the error message:

CUBYDR: Departure point out of bounds: jcen,icount,pgls= 39, 1726, 1728

which seems to have to do with the length of the time step.
I use the T31 resolution with a time step

DTIME=1800

as it should be for this resolution. The problem seems to be solved by just setting the time step to 1200
seconds as is recomended for the T42 resolution. However, then physical parametrizations also change, and I
don't know what I have to expect from that. Can I just change the time step without changing other
parameters?

It would be nice if I could get some help with that.

Best regards,

Anna

--------------------------------
Dr. Anna von der Heydt
Institute for Marine and Atmospheric Research
Utrecht University
The Netherlands

The nominal time step to use with the model is really controlled by
the strength of the wind field, in relation to a CFL criterion. For present day conditions the strongest winds occur in the northern hemisphere polar night in the middle atmosphere, and it is this wind speed that
controls the required time step length. Shifting the continents etc will
obviously change the wind behavior and it is no surprise to me that
you require a smaller time step. My response to your question about
the possible need for retuning is that it depends on your experimental setup. If you are going to compare to a present day simulation you would want to run both simulations with the same (shorter) time step length.
Then, depending on how far off your present day simulation is, you will need to consider the need for a retuning exercise.

Phil