[10460] | 1 | ***************** |
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| 2 | Data assimilation |
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| 3 | ***************** |
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[10201] | 4 | |
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| 5 | .. contents:: |
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| 6 | :local: |
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| 7 | |
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| 8 | The assimilation interface to NEMO is split into three modules. |
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| 9 | |
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[11707] | 10 | - ``OBS`` for the observation operator |
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| 11 | - ``ASM`` for the application of increments and model bias correction |
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| 12 | (based on the assimilation increments). |
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| 13 | - ``TAM`` the tangent linear and adjoint model. |
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| 14 | |
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| 15 | Please see |DOI man OCE|_ for more details including information about the input file formats and |
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[10201] | 16 | the namelist settings. |
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| 17 | |
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[11707] | 18 | Observation and model comparison (``OBS``) |
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| 19 | ========================================== |
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[10201] | 20 | |
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[11707] | 21 | The observation and model comparison code (OBS) reads in observation files |
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| 22 | (profile temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration, |
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| 23 | and velocity) and calculates an interpolated model equivalent value at |
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| 24 | the observation location and nearest model timestep. |
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[10201] | 25 | The resulting data are saved in a feedback file (or files). |
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| 26 | The code was originally developed for use with the NEMOVAR data assimilation code, but |
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| 27 | can be used for validation or verification of model or any other data assimilation system. |
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| 28 | This is all controlled by the namelist. |
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[11707] | 29 | To build with the OBS code active ``key_diaobs`` must be set. |
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[10201] | 30 | |
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[11707] | 31 | More details in |DOI man OCE|_ "Observation and Model Comparison (``OBS``)" chapter. |
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[10201] | 32 | |
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[11707] | 33 | Standalone observation operator (``SAO``) |
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| 34 | ----------------------------------------- |
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[10201] | 35 | |
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| 36 | The OBS code can also be run after a model run using saved NEMO model data. |
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| 37 | This is accomplished using the standalone observation operator (SAO) |
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| 38 | (previously known the offline observation operator). |
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| 39 | |
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| 40 | To build the SAO use makenemo. |
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| 41 | This means compiling NEMO once (in the normal way) for the chosen configuration. |
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[11713] | 42 | Then include ``SAO`` at the end of the relevant line in :file:`cfg.txt` file. |
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| 43 | Then recompile with the replacement main program in :file:`./src/SAO`. |
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| 44 | This is a special version of :file:`nemogcm.F90` (which doesn't run the model, |
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[11707] | 45 | but reads in the model fields, and observations and runs the OBS code. |
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| 46 | See "Standalone observation operator (``SAO``)" section in |DOI man OCE|_. |
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[10201] | 47 | |
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[11707] | 48 | Apply assimilation increments (``ASM``) |
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| 49 | ======================================= |
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[10201] | 50 | |
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| 51 | The ASM code adds the functionality to apply increments to the model variables: |
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| 52 | temperature, salinity, sea surface height, velocity and sea ice concentration. |
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[11707] | 53 | These are read into the model from a NetCDF file which |
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| 54 | may be produced by separate data assimilation code. |
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[10201] | 55 | The code can also output model background fields which are used as an input to data assimilation code. |
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[11707] | 56 | This is all controlled by the namelist ``&nam_asminc``. |
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[10201] | 57 | To build the ASM code ``key asminc`` must be set. |
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| 58 | |
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[11707] | 59 | More details in |DOI man OCE|_ "Apply Assimilation Increments (``ASM``)" chapter. |
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[10201] | 60 | |
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[11707] | 61 | Tangent linear and adjoint (``TAM``) |
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| 62 | ==================================== |
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[10201] | 63 | |
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| 64 | This is the tangent linear and adjoint code of NEMO which is useful to 4D VAR assimilation. |
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