1 | ***************** |
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2 | Data assimilation |
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3 | ***************** |
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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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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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16 | the namelist settings. |
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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 |
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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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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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29 | To build with the OBS code active ``key_diaobs`` must be set. |
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30 | |
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31 | More details in |DOI man OCE|_ "Observation and Model Comparison (``OBS``)" chapter. |
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32 | |
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33 | Standalone observation operator (``SAO``) |
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34 | ----------------------------------------- |
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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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42 | Then include ``SAO`` at the end of the relevant line in ``cfg.txt`` file. |
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43 | Then recompile with the replacement main program in ``./src/SAO``. |
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44 | This is a special version of ``nemogcm.F90`` (which doesn't run the model, |
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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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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 |
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54 | may be produced by separate data assimilation code. |
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55 | The code can also output model background fields which are used as an input to data assimilation code. |
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56 | This is all controlled by the namelist ``&nam_asminc``. |
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57 | To build the ASM code ``key asminc`` must be set. |
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58 | |
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59 | More details in |DOI man OCE|_ "Apply Assimilation Increments (``ASM``)" chapter. |
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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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