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geoschem / gchp_legacy

Repository for GEOS-Chem High Performance: software that enables running GEOS-Chem on a cubed-sphere grid with MPI parallelization.
http://wiki.geos-chem.org/GEOS-Chem_HP
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[QUESTION] The dimensions of gchp restart file #72

Closed hongjianweng closed 4 years ago

hongjianweng commented 4 years ago

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hongjianweng commented 4 years ago

The dimensions of restart file for gchp are different from GEOS-Chem Classic. Take initial_GEOSChem_rst.c24_standard.nc for example: 1 netcdf initial_GEOSChem_rst.c24_standard { 2 dimensions: 3 lon = 24 ; 4 lat = 144 ; 5 lev = 72 ; 6 time = 1 ; lon = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 ; lat = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144 ; } As shown above, this is the region restart file, not the global file. Why not use a global file? Does it affect the simulation?

lizziel commented 4 years ago

Hi @hongjianweng,

Thanks for reaching out about this since it is rather confusing. The latitude and longitude values in the files are indexes and not actual latitude and longitude values. The mapping of these indexes to the global cubed-sphere grid is specific to the NASA GEOS system and is done internally within GCHP. For the case of c24, there are 6 faces of 24x24 grid cells, so a total of 3456 cells. This matches the total number of unique (lat,lon) indexes in the file (24*144). To cover all faces, the latitude index is unique across all faces and so goes from 1 to 24*6. This allows the fewest possible dimension values to get unique (lat,lon) index combinations for all 3456 cells. Does this make sense?

You may notice that the GCHP output diagnostics have a different format for exactly the same c24 grid. In those files the face dimension is split from latitude and longitude. This is because the GMAO MAPL library handles restarts and diagnostics separately. They have not yet updated their restart code to use the same new format as the diagnostics. Hopefully this will change in the future to avoid this kind of confusion, as well as the need for post-processing if using the output of the two types of files in the same computation.

lizziel commented 4 years ago

I am closing out this issue. Feel free to reopen if you have still have questions after reading my explanation above.