Nudging namelist confusion

[arunn]

Hi,
I am running a month-long simulation. I'm trying to nudge the meteorological fields every 24hrs.
For this, issuing these in the namelist before running real.

 grid_fdda                           = 1
 gfdda_inname                        = 'wrffdda_d<domain>'
 gfdda_interval_m                    = 1440
 gfdda_end_d                         = 30
 io_form_gfdda                       = 2

However the wrffdda file, I get met fields and 'Times' stamps every 6 hours daily.
What am I doing wrong here?

 

[kwerner]

Hi,
The wrffdda file will have times that match the boundary condition times in your wrfbdy file. However, since you set the gfdda_interval_m = 1440, then nudging will only happen every 24 hours. If you have a reason for only nudging less often than the times are available, it will be fine. You will just get warning messages in the output, like

**WARNING** Time in input file not equal to time on domain **WARNING**
 **WARNING** Trying next time in file wrffdda_d01 ...

but it should run to completion. Otherwise, you could just set the interval to the 6-hour interval available in the wrffdda file.

 

[arunn]

Thanks, kwerner for the clarification.
I have one more doubt, what does fgdt do? In the user manual, it is said "calculation frequency (in mins) for analysis nudging; 0=every time step (which is recommended)"
But I am not really sure how to interpret it. Could you please explain

 

[kwerner]

Similar to the model time step (time_step), this value (fgdt) is the time step that is used for nudging. This is how often the model is nudged, and you can set to a value different from the model time_step, but there is not usually a need to do so. As it states, it's recommended to leave that value as 0, which means nudging will happen with every model time_step.

 

[arunn]

Thanks once again, Kwerner!

 

[wangjm]

Hi, I am also confused about the two parameters "gfdda_interval_m" and "guv", how to understand "guv"? do the have the relationship like this: "gfdda_interval_m*60 =1/guv "? however, the example from Steps to run analysis nudging: ( the following picture) seems to have no such relationship. Thank you.

 

[kwerner]

Hi, I am also confused about the two parameters "gfdda_interval_m" and "guv", how to understand "guv"? do the have the relationship like this: "gfdda_interval_m*60 =1/guv "? however, the example from Steps to run analysis nudging: ( the following picture) seems to have no such relationship. Thank you.

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