How to set the time step to 0.2 seconds?

[KiyoTom]

Hello all!

How do I set the time step to 0.2 seconds when doing data assimilation by 4DVar?

I am forecasting a 2 domain model and want to do data assimilation with 4DVar for domain 2.

When I was forecasting a 2-domain model without data assimilation, I was able to forecast domain 2 with a 0.2 second time step by specifying a time step in namelist.input.

&domains
time_step = 2,
time_step_fract_num = 0,
time_step_fract_den = 1,
parent_time_step_ratio = 1, 10,
/

Specifying namelist.input for data assimilation by 4DVar resulted in the error For 4DVAR, in the &domains namelist, "time_step" must be set to a non-zero value.

&domains
time_step = 0,
time_step_fract_num = 2,
time_step_fract_den = 10,
/

How do I set a time step of 0.2 seconds?

Best regards.

 

[Ming Chen]

Your option below is correct for setting a time_step of 0.2.

&domains
time_step = 0,
time_step_fract_num = 2,
time_step_fract_den = 10,
/

Unfortunately DA has special requirement for time step. I don't think time step of 0.2 could work for DA.

 

[KiyoTom]

Hi Ming.

Thanks for the reply.

When I run 4DVar with the namelist.input settings you gave me, I get an error.

---------------------------- FATAL ERROR -----------------------
Fatal error in file:  da_solve.inc  LINE:     113
For 4DVAR, in the &domains namelist, "time_step" must be set to a non-zero value
----------------------------------------------------------------

For 3DVar, there is no error.

If you look around line 113 of "da_solve.inc", it checks if time_step is zero only in the case of 4DVar.

Best regards.

 

[KiyoTom]

Thank you.

I also adjusted the size of the model and reconfigured it to run in integer seconds.

Best regards.