[10201] | 1 | Data assimilation |
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| 2 | ================= |
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| 3 | |
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| 4 | .. include:: .global.rst |
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| 5 | |
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| 6 | .. contents:: |
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| 7 | :local: |
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| 8 | |
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| 9 | The assimilation interface to NEMO is split into three modules. |
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| 10 | - OBS for the observation operator |
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| 11 | - ASM for the application of increments and model bias correction (based on the assimilation increments). |
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| 12 | - TAM the tangent linear and adjoint model. |
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| 13 | |
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| 14 | Please see the `NEMO reference manual`_ for more details including information about the input file formats and |
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| 15 | the namelist settings. |
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| 16 | |
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| 17 | -------------------------------------- |
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| 18 | Observation and model comparison (OBS) |
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| 19 | -------------------------------------- |
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| 20 | |
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| 21 | The observation and model comparison code (OBS) reads in observation files (profile temperature and salinity, |
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| 22 | sea surface temperature, sea level anomaly, sea ice concentration, and velocity) and |
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| 23 | calculates an interpolated model equivalent value at the observation location and nearest model timestep. |
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| 24 | The resulting data are saved in a feedback file (or files). |
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| 25 | The code was originally developed for use with the NEMOVAR data assimilation code, but |
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| 26 | can be used for validation or verification of model or any other data assimilation system. |
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| 27 | This is all controlled by the namelist. |
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| 28 | To build with the OBS code active ``key_diaobs`` must be set. |
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| 29 | |
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| 30 | More details in the `NEMO reference manual`_ chapter 12. |
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| 31 | |
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| 32 | Standalone observation operator (SAO) |
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| 33 | ------------------------------------- |
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| 34 | |
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| 35 | The OBS code can also be run after a model run using saved NEMO model data. |
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| 36 | This is accomplished using the standalone observation operator (SAO) |
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| 37 | (previously known the offline observation operator). |
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| 38 | |
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| 39 | To build the SAO use makenemo. |
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| 40 | This means compiling NEMO once (in the normal way) for the chosen configuration. |
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| 41 | Then include ``SAO`` at the end of the relevant line in ``cfg.txt`` file. |
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| 42 | Then recompile with the replacement main program in ``./src/SAO``. |
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| 43 | This is a special version of ``nemogcm.F90`` (which doesn't run the model, but reads in the model fields, and |
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| 44 | observations and runs the OBS code. |
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| 45 | See section 12.4 of the `NEMO reference manual`_. |
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| 46 | |
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| 47 | ----------------------------------- |
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| 48 | Apply assimilation increments (ASM) |
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| 49 | ----------------------------------- |
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| 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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| 53 | These are read into the model from a NetCDF file which may be produced by separate data assimilation code. |
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| 54 | The code can also output model background fields which are used as an input to data assimilation code. |
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| 55 | This is all controlled by the namelist nam_asminc. |
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| 56 | To build the ASM code ``key asminc`` must be set. |
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| 57 | |
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| 58 | More details in the `NEMO reference manual`_ chapter 13. |
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| 59 | |
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| 60 | -------------------------------- |
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| 61 | Tangent linear and adjoint (TAM) |
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| 62 | -------------------------------- |
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| 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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| 65 | |
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| 66 | .. _NEMO reference manual: http://doi.org/10.5281/zenodo. |
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