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Good afternoon, I am coupling a reduced Gaussian grid atmosphere (OpenIFS) with an variable resolution unstructured grid ocean model (FESOM2). I would like use OASIS3-MCT conservative remapping for the atmospheric fluxes. Does oasis_write_corner work with an unstructured mesh? I calculate the "corners" around a mesh point as the center points of adjacent scalar volumes. In the open ocean we have about 6 adjacent scalar volumes (can be different between grid points). Near the coast this can go down all the way to 3 in narrow inlets. In areas of resolution change we can have as many as 8 adjacent scalar volumes and subsequently 8 corners. I am giving oasis_write_corners the maximum number of corners (8) in the grid and the missing corners (if less than 8) are replaced by repeating the first corner. I have gotten no complains from oasis_write_corners after doing this. I have however run into an issue where the flux values received by the ocean are many orders of magnitude bigger than those send by the atmosphere. I suspect there might be a connection with the corners messing up the conservative remapping? For a test case I send the value 1 everywhere and receive 2858036804.74055 on the ocean side. My namcouple configuration is: # --- Stresses for oce and ice --- [ifs fesom] A_TauX_oce:A_TauY_oce:A_TauX_ice:A_TauY_ice taux_oce:tauy_oce:taux_ico:tauy_ico 1 2700 3 rstas.nc EXPORTED A128 feom LAG=0 P 0 P 0 LOCTRANS SCRIPR CONSERV AVERAGE GAUSWGT D SCALAR LATITUDE 1 9 2.0 GLOBAL Best regards, Jan Streffing
Hi Jan, - If you want to perform a conservative remapping you must use in your namcouple (see the User Guide https://oasis.cerfacs.fr/wp-content/uploads/sites/114/2021/02/GLOBC-TR-oasis3mct_UserGuide3.0_052015.pdf, section 4.3) : CONSERV D SCALAR LATITUDE 1 FRACNNEI FIRST - You must provide grids.nc, masks.nc and areas.nc - The option CONSERV after SCRIPR will redistribute on the target grid the difference of the fuxes integrated on the source and the target grids (see the User Guide https://oasis.cerfacs.fr/wp-content/uploads/sites/114/2021/02/GLOBC-TR-oasis3mct_UserGuide3.0_052015.pdf, section 4.4, the options of CONSERV) - When you do remapping with gaussian reduced grid as a source grid, you must put north_thresh = 2.00_dbl_kind and south_thresh =-2.00_dbl_kind in oasis3-mct/lib/scrip/scr/remap_conserv.F and recompile OASIS3-MCT - You can use oasis_write_corner with an unstructured mesh - Your "volumes" must have no holes and cover the entire domain of simulation. By the way how do you define the adjacent scalar volumes ? From the other points ? Best regards, Laure
Hey Laure, thank you for the input. I changed north_thresh which was 1.45 before and replaced the scripr options. That seems to have done the trick. I have not yet verified that the fluxes are acutally conserved but the model no longer crashes due to erroneously large values. Progress! I have one more question. Could you elaborate on the function of north_thresh / south_thresh? You said I must use +-2.00. I also work on EC-Earth, and the OASIS source code I used was taken from the EC-Earth Model. There we do conservative remapping with a reduced gaussian source grid and we have north_thresh = 1.45_dbl_kind and south_thresh =-2.00_dbl_kind. Is that something we should worried about in the EC-Earth conserv remapping? Cheers, Jan
Hi Jan, north_thresh=+2 rad corresponds to lat=90° and south_thresh=-2 rad corresponds to lat=-90° The Lambert projection used for latitudes above north_thresh (south_thresh) give false results for the Gaussian reduced grid as the borders of the cells do not coincide in the projected space; this is because a corner of the cell is not necessarily a corner of the neighbour cell on a higher or lower latitude band. So you have to put north_thresh > 1.571 (=2) so to deactivate the projection in EC Earth. Best regards, Laure
