Page Comparison

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1. fluxes:  
   1. if source grid resolution >> target grid resolution:   FV→FV aave 
   2. if source grid resolution <= target grid resolution:   V3 is considering adopting TR 2nd-order with non-linear correction ("nlmap").  /wiki/spaces/COM/pages/3771301899 FV2+CAAS 
2. state and vector maps:  
   1. ocn→atm: currently this map must be the same as used for fluxes (FV→FV aave)
      1. This restriction is because the range of the state and vector maps must match the range of the flux map.  
      2. The "nlmap" FV2+CAAS  approach should be used for this map as well used  (not sure if this was tested in time for V3?).        
   2. lnd↔atm and atm→ocn
      1. if source grid resolution >> target grid resolution (fine-to-coarse):  "FV→FV aave"  
      2. if source grid resolution <= target grid resolution (nearly equivalent resolutions):   Use TR bilin
      3. if source grid resolution << target grid resolution (coarse-to-fine):  TR 2nd-order with non-linear correction ("nlmap")FV2+CAAS.   Needed for atm→lnd in trigrid.
      4. Why do we still recommend aave or bilin above?  intbilin or "nlmap" FV2+CAAS approach should be better in both cases.  
   3. riv → ocn
      1. continue to use custom maps generated by E3SM/cime/tools/mapping/gen_mapping_files/runoff_to_ocn

"FV2+CASS" refers to the nonlinear approach from /wiki/spaces/COM/pages/3771301899 where an aave and 2nd order FV map are used with Compute-And-Assured-Sum (CAAS) to provide a monotone conservative map that avoids the blocky artifacts of aave maps and is more accurate than aave maps.  

E3SMv2 with pg2

ATM FV grids with physics on the 2x2 physgrid (i.e. pg2) coupled to FV ocean and FV land. E3SMv2 will still use the spectral element dynamical core on the GLL grid, but the coupling between component always happens between the physics columns, which are now on a FV grid. 

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