Using 'lat-lon' map projection in WRF, assigns Cassini projection in DART

[braczka]

### Describe the bug

When using WRF-DART while applying WRF 'lat-lon' map projection for land/atmosphere -- DART misinterprets 'lat-lon' map projection as cassini.

Expectation:
When using WRF 'lat-lon', that DART uses the map_latlon and PROJ_LATLON options in model_mod to perform interpolation

What happens instead:
DART uses map_cassini and PROJ_CASSINI instead. This occurs because WRF assign an integer value of '6' for the 'MAP_PROJ' attribute using map_latlon, whereas DART assigns an integer value of '0' for PROJ_latlon. DART incorrectly calls subroutine llij_cassini instead of llij_latlon, which is the incorrect forward operator.

### Which model(s) are you working with?
Tested with WRF version 3.9 thru 4.5

### Version of DART
Latest tag

### Have you modified the DART code?
No -- but quick fix would be to reassign the integers within DART such that PROJ_LATLON = 6 and map_latlon = 6. Then assign cassini a different integer, such as PROJ_CASSINI = 106 or map_cassini = 106. See misc_definitions_module and
model_mod.f90 for more details.

All other WRF supported map projections are aligned properly with DART -- including lambert, mercator and polar. No changes required. The WRF-DART tutorial using the lambert map projection.

I thought this integer change for the latlon MAP_PROJ occured between WRF version 3 and more recent versions of WRFv4+, and this change was missed during the WRF-DART version 4 tutorial updates, however, both WRFv3 and v4 versions have this integer mismatch with DART.

Bug, first reported by Rui Sun (UCSD).

### Compiling information
Derecho using gfortan

[braczka]

Forgot to mention that DART uses the MAP_PROJ integer attribute from the WRF land/atm files to assign the integer in DART. This is read within read_wrf_file_attributes

[nancycollins]

what would happen with WRF files that did have 0 as the projection type integer? would those still work?

[braczka]

I don't know if WRF generates MAP_PROJ = 0 anymore. I guess at some point it did, perhaps the 'lat-lon' projection at one point was at '0', but testing version 3.9 for the latest versions 4.5 does not produce MAP_PROJ = 0 for any supported map projection that I can tell.

Currently, if MAP_PROJ = 0, DART interprets as 'lat-lon' which is incorrect. If I implemented suggested changes, a MAP_PROJ = 0 should cause DART to error out.

[nancycollins]

just for reference, i looked up some older wrfinput_d01 files from CONUS runs and they use map projection 1. so maybe this change wouldn't break anything.

[braczka]

just for reference, i looked up some older wrfinput_d01 files from CONUS runs and they use map projection 1. so maybe this change wouldn't break anything.

What was the WRF version of the wrfinput_d01? As far as I know map projection 1 has always referred to the lambert projection
Projection 1 --> lambert
Projection 2 --> polar
Projection 3 --> mercator
Projection 6 --> lat-lon, although at some point was '0' according to DART.

I would need to dig into the WRF code (WPS ) to find all possibilities when I find time

[nancycollins]

yes - the conus runs i usually saw were using a lambert projection, not straight lat/lon. plotted on a lat/lon grid, the area was a section of a wedge, not a square. that was one of the reasons we used the wrf utils to map from lat/lon to i/j index in the wrf arrays.