Analysis resolution for grid nudging

[andreas-h]

I'm planning to run WRF(-Chem) using the new ERA5 reanalysis as initial/boundary condition.

My outermost domain (centered at 35N) has 81km resolution, and in 5 nests I'm going down to 1km. The reason for this is that my chemical boundary conditions are very coarse (3x2) and I want to give them time to go down to the target resolution of 1x1km.

ERA5 comes in 0.25 degree resolution. Now this is a lot finer than the 81km of my outer domain.

QUESTION: When analysis-nudging my two outer domains (81km and 27km), should I nudge them both to the same resolution ERA5? Or should I rather prepare the fdda input files (using real.exe) for the 81km domain with coarse ERA5 data, and for the 27km domain with original ERA5 resolution? (or something in between, e.g., 0.5 or 0.375 degree)?

 

[Ming Chen]

I would suggest you nudge the same resolution ERA5 data (the one your initial and boundary files derived from) into your 81-km and 27-km domains.

By the way, if you use new ERA5 data (0.25 degree) to drive WRF, why do you need to run 5-nested domains? If you are only concerned of the simulation in high-resolution domain, you may run in triple-nested domains like 9-3-1km.