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WRFDA for nested domains

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I've been searching the forum and documentation but still no luck for a more detailed explanation of running 4dvar for both the parent and nested domains of a WRF forecast simulation setup.

It's clear that no nesting is supported in WRFDA and one must separately run 4dvar for each domain.

After running real.exe for a 2 way nested run you get the wrfbdy_d01 boundary file only for the parent domain, needed for the assimilation together with wrfinput_d01.
1. How do we continue with the nested domains? Which boundary conditions file wrfbdy_d0? do we use for the nested domains.
Are the namelist.input options grid_id, parent_id, i&j_parent_start relevant when assimilating data over the nested domains?
2. Do we have to use ndown to provide wrfbdy_d02, d03, etc. ?
3. Do we have to run WPS and WRF in single domain mode for each domain (parent and child domains)?

Any help will be appreciated,
You are right that WRFDA does not support nested run and you have to run WRFDA separately for different domains.
So for 4DVAR, you need to create a wrfbdy file for each domain you want to analyze.