CONTROL options

[akp]

I am wondering about option 15 (from users guide) in the CONTROL file: Number of simultaneous concentration grids. Is this for the output or input? I defined my grid with two nested model domains. From the users guide though it says if you define your grid over grids with differing resolution, hysplit will account for this if you specify the most fine resolution desired. If this is the case then what is the use of setting this parameter in the control file? Output can simply be displayed over differing grids without writing out to sperate grids.

[glenn.rolph]

I think you are confusing the input meteorological grid section of the CONTROL file (#7 in Users Guide) with the output concentration grid section (#15). HYSPLIT will perform its calculation internally at the meteorological grid resolution you provide, however you can define the concentration output grids independently from the meteorological grid resoutions and you do this in section 15 of the CONTROL file.

[akp]

I guess I am still a bit confused about this. Based on your explaination this is how I understand it now. If I have a large 3-km nest and a smaller 1-km nest for input and I produce output for a region that encompasses both grids at 1.0km then my output is at 1.0km for the entire output grid. But if instead I wanted two output grids to match the 1.0 and 3.0km inputs I could also do this by specifying 2 for item 15 in teh Control file and then fitting the hysplit grids to the met grids in items 16-18 and then name them in 19-20.

[akp]

So in essence if I just keep my settings as is - with two varied input resolutions and one output resolution, the output is being interpolated down to scale for the area of the domain where only the course resolution exists as input? But I could change this to have output match input domains by adding additional options for options 16-20.

[glenn.rolph]

No, the output concentration grid is totally independent on the meteorological grid resolution (input data). You must define an output grid in the CONTROL file otherwise you will run the model but not produce concentration output (it does not default to the input meteorological grid). Therefore, you can define one or multiple resolution output grids in the CONTROL file, but you must define at least one to get output.