*** IFS analyses for ECOMIP Robin Hogan 24 September 2025 Updated 2 October 2025 FILES The subdirectories from this directory contains global atmospheric and surface analyses for initializing forecasts as part of ECOMIP - the EarthCARE-ORCESTRA Model Intercomparison Project. The filename format is ecomip_ifs_od-0001_analysisTZ__. where "ifs" indicates ECMWF's Integrated Forecasting System, od-0001 is the class/experiment-id of the operational 9-km forecasts, is the date of the analysis, is the time of the analysis, is either "native-grid" indicating the cubic-octahedral of the IFS or "0.05deg" indicating a regular longitude-latitude grid with 0.05 degree resolution, is "ml" for model-level fields and "sfc" for surface and single-level fields, while is either "nc" for NetCDF4/HDF5 format or "grib" for GRIB format. Note that the native grid is only provided in GRIB format. PRESSURE COORDINATE The IFS is a hydrostatic model that uses a terrain-following hybrid pressure vertical coordinate system. The model consists of 137 levels which can be thought of as layers of finite thickness defined by the pressure at the 138 "half-levels" between them, including the surface and the top-of-atmosphere (where the pressure is zero). The pressure of half-level i, in Pascals, counting from 0 at top-of-atmosphere to 137 at the surface, is given by p_i = a_i + b_i * exp(lnsp) where "lnsp" is the logarithm of the surface pressure given in the model-level ("ml") files (even though it is not a function of level), and the "a" and "b" coefficients are given by: ---half-level-index--- ---a-coefficient--- ---b-coefficient--- 0 0 0 1 2.000365 0 2 3.102241 0 3 4.666084 0 4 6.827977 0 5 9.746966 0 6 13.605424 0 7 18.608931 0 8 24.985718 0 9 32.98571 0 10 42.879242 0 11 54.955463 0 12 69.520576 0 13 86.895882 0 14 107.415741 0 15 131.425507 0 16 159.279404 0 17 191.338562 0 18 227.968948 0 19 269.539581 0 20 316.420746 0 21 368.982361 0 22 427.592499 0 23 492.616028 0 24 564.413452 0 25 643.339905 0 26 729.744141 0 27 823.967834 0 28 926.34491 0 29 1037.201172 0 30 1156.853638 0 31 1285.610352 0 32 1423.770142 0 33 1571.622925 0 34 1729.448975 0 35 1897.519287 0 36 2076.095947 0 37 2265.431641 0 38 2465.770508 0 39 2677.348145 0 40 2900.391357 0 41 3135.119385 0 42 3381.743652 0 43 3640.468262 0 44 3911.490479 0 45 4194.930664 0 46 4490.817383 0 47 4799.149414 0 48 5119.89502 0 49 5452.990723 0 50 5798.344727 0 51 6156.074219 0 52 6526.946777 0 53 6911.870605 0 54 7311.869141 0 55 7727.412109 7e-06 56 8159.354004 2.4e-05 57 8608.525391 5.9e-05 58 9076.400391 0.000112 59 9562.682617 0.000199 60 10065.978516 0.00034 61 10584.631836 0.000562 62 11116.662109 0.00089 63 11660.067383 0.001353 64 12211.547852 0.001992 65 12766.873047 0.002857 66 13324.668945 0.003971 67 13881.331055 0.005378 68 14432.139648 0.007133 69 14975.615234 0.009261 70 15508.256836 0.011806 71 16026.115234 0.014816 72 16527.322266 0.018318 73 17008.789062 0.022355 74 17467.613281 0.026964 75 17901.621094 0.032176 76 18308.433594 0.038026 77 18685.71875 0.044548 78 19031.289062 0.051773 79 19343.511719 0.059728 80 19620.042969 0.068448 81 19859.390625 0.077958 82 20059.931641 0.088286 83 20219.664062 0.099462 84 20337.863281 0.111505 85 20412.308594 0.124448 86 20442.078125 0.138313 87 20425.71875 0.153125 88 20361.816406 0.16891 89 20249.511719 0.185689 90 20087.085938 0.203491 91 19874.025391 0.222333 92 19608.572266 0.242244 93 19290.226562 0.263242 94 18917.460938 0.285354 95 18489.707031 0.308598 96 18006.925781 0.332939 97 17471.839844 0.358254 98 16888.6875 0.384363 99 16262.046875 0.411125 100 15596.695312 0.438391 101 14898.453125 0.466003 102 14173.324219 0.4938 103 13427.769531 0.521619 104 12668.257812 0.549301 105 11901.339844 0.576692 106 11133.304688 0.603648 107 10370.175781 0.630036 108 9617.515625 0.655736 109 8880.453125 0.680643 110 8163.375 0.704669 111 7470.34375 0.727739 112 6804.421875 0.749797 113 6168.53125 0.770798 114 5564.382812 0.790717 115 4993.796875 0.809536 116 4457.375 0.827256 117 3955.960938 0.843881 118 3489.234375 0.859432 119 3057.265625 0.873929 120 2659.140625 0.887408 121 2294.242188 0.8999 122 1961.5 0.911448 123 1659.476562 0.922096 124 1387.546875 0.931881 125 1143.25 0.94086 126 926.507812 0.949064 127 734.992188 0.95655 128 568.0625 0.963352 129 424.414062 0.969513 130 302.476562 0.975078 131 202.484375 0.980072 132 122.101562 0.984542 133 62.78125 0.9885 134 22.835938 0.991984 135 3.757813 0.995003 136 0 0.99763 137 0 1 See also https://confluence.ecmwf.int/display/UDOC/L137+model+level+definitions The mean pressure of each level/layer is simply taken to be the linear mean of the half-level pressures at the top and bottom of the layer. SURFACE OROGROPHY The height of the orography in the model may be computed by dividing the geopotential "z" in the surface ("sfc") file by standard gravitational acceleration (9.80665 m/s.) REGRIDDING The recommended way to convert the files to the grid of your own model is to use the "cdo" tool with conservative remapping, applied to the two files on the native grid. First create a file of weights as follows: cdo -f nc gencon, -setgrid,TCo1279_grid.nc weights.nc where TCo1279_grid.nc is a file provided in this directory that describes the ECMWF 9-km model grid, and is an equivalent file for your own model. is then one of the IFS grib files you want to convert, e.g. ecomip_ifs_od-0001_analysis20240902T0000Z_native-grid_sfc.grib. Then remap the input file with: cdo -f nc --eccodes remap,,weights.nc -setgrid,TCo1279_grid.nc The output file will be in NetCDF format. CONTACT If you have any problems converting to your own format, please first look at the cdo documentation (https://zenodo.org/records/10020800) - if you are still stuck I will try to direct your query to someone who can help.