At least that is what I do and it does well
@William.Hatheway Thanks, but I think it could be start at higher values like 25 Km!At least that is what I do and it does well
There is no need to use a domain that coarse when the input data have a grid spacing of 0.25 degrees. The ratio between the input data and your parent domain should be somewhere between 3:1 and 5:1, and starting with 9km falls within that interval. And then it is perfectly fine to use a 3:1 ratio between the parent and child (i.e., 9km, 3km).Thanks, but I think it could be start at higher values like 25 Km!
@kwerner thanks for your reply. I need to use a coarse domain (27 km) because I use chem_opt 202 which runs normally slow.There is no need to use a domain that coarse when the input data have a grid spacing of 0.25 degrees. The ratio between the input data and your parent domain should be somewhere between 3:1 and 5:1, and starting with 9km falls within that interval. And then it is perfectly fine to use a 3:1 ratio between the parent and child (i.e., 9km, 3km).
@kwerner So many thanks for your advice. But in one case I experienced something different. I considered 3 domains with 18, 9, and 3 km. I set thime_step to 72 seconds.I'm actually not sure what will happen if you use a domain that is more coarse than the input data. This is not something I've ever tested, but you could give it a try and see what happens.
Just so you know, although you set time_step for your outer domain (in this case, 27km), the variable parent_time_step_ratio (which is typically set to the same value as the parent_grid_ratio) determines the time_step for the child domains. Therefore, if your dx/dy = 27, 9, 3, and let's say, for example, that you set time_step = 135, then the model will still run a time step of the following per domain
d01 = 135
d02 = 45 (3 times to reach the d01 time step)
d03 = 15 (9 times to reach the d01 time step)
It would look something like this
d01: 0_________________________________________________________________135
d02: 0_____________________45
d03: 0_____15______30______45
d02: 45_____________________90
d03: 45______60______75_____90
d02: 90__________________135
d03: 90_____105____120__135
d01: 135_______________________________________________________270
...etc.
So including a larger parent domain is simply only adding additional time_steps you don't need, and ultimately will make the simulation longer.