the coordinate transfo error exceeds 0.02*dx

[victoria.sinclair@…]

I am trying to run FLEXPART-WRF (forward) using WRF input data on a mercator grid. I keep getting the error:

test_xyindex_to_ll_wrf calling map_set -- map_proj_id, map_set_proj_code = 3 1

test_xyindex_to_ll_wrf -- lgrid, rmserr (km) = 0 1.03E+03

• *
• WARNING - the coordinate transfo error exceeds 0.02*dx *
• *

problem with the projection. wrf+flexpart stops.

I have attached my input file I am using. The WRF output is at 9km grid spacing and has 249 points in the east-west direction and 255 points in the north-south direction. Any advice in how to solve this problem would be appreciated.

[victoria.sinclair@…]

input file

[adingwell]

Hi Victoria,

the error you get is due to large scaling errors from your map projection. FLEXPART-WRF makes a test for this to prevent the user from setting up too distorted grids. You can view the scaling errors in your WRF-output (the MAPFAC_* fields). FLEXPART-WRF is hard-coded to abort if the error is above 2%.

You can solve this problem by:

• Changing the map projection to something more suitable for the region you're studying
• Setting up a smaller model domain in flexpart-wrf (the highest errors are usually near the domain borders unless you're using an unsuitable map projection)
• Changing the threshold in map_proj_wrf.f90 (not recommended)

[adingwell]

I'm marking this as solved due to inactivity.

[ahilboll]

We're running in the same problem here with WRF output on 40m resolution. The MAPFAC_ values are all below 1.0002, using Lambert projection. So in principle, the domain should not affected by scaling.

So I don't understand how come that the RMS is above 2%. Do WRF and FLEXPART-WRF use different formulas to calculate lat/lon from the map projection parameters?

And, for now, more importantly: Can we safely use the WRF output in this situation?

[pesei]

Replying to ahilboll:

So I don't understand how come that the RMS is above 2%. Do WRF and FLEXPART-WRF use different formulas to calculate lat/lon from the map projection parameters?

They should not but maybe there have been changes in newer versions of WRF? Might be worthwhile to compare.

[ahilboll]

Replying to pesei:

Replying to ahilboll:

So I don't understand how come that the RMS is above 2%. Do WRF and FLEXPART-WRF use different formulas to calculate lat/lon from the map projection parameters?

They should not but maybe there have been changes in newer versions of WRF? Might be worthwhile to compare.

I just compared map_proj_wrf_subaa.f90 from FLEXPART-WRF v3.3.2 to module_llxy.F from WRF v4.1 and the respective ijll_lc subroutines seem to be equivalent.