.. _recipes_esaccioc:
   
Ocean chlorophyll in ESMs compared to ESA-CCI observations.
===========================================================

Overview
--------

This recipe compares monthly surface chlorophyll from CMIP models to ESA CCI ocean colour chlorophyll (ESACCI-OC). The observations are the merged sensor geographic monthly L3S chlor_a data Sathyendranath et al. (2019). Multiple models and different observational versions can be used by the script.

The recipe_esacci_oc.yml produces an image showing four maps. Each of these four maps shows latitude vs longitude and the chlorophyll value. The four plots are: ESACCI-OC v5.0 chlorophyll, the CMIP6 model, the bias model-observation and the ratio model/observations. The script also produces a scatter plot for all coordinates with the model on the x-axis and the observations on the y axis and a line of best fit with the parameter values given in the panel.


Available recipes and diagnostics
---------------------------------

Recipes are stored in esmvaltool/recipes/ocean/

    * recipe_esacci_oc.yml

Diagnostics are stored in esmvaltool/diag_scripts/ocean/

    * diagnostic_model_vs_obs.py


User settings in recipe
-----------------------

#. Script diagnostic_model_vs_obs.py

   *Required settings for script*

   * observational_dataset: name of reference dataset (e.g. {dataset: ESACCI-OC,})


Variables
---------

* chl (ocean, monthly mean, longitude, latitude, time)


Observations and reformat scripts
---------------------------------

* ESACCI-OC (chl)

  *Reformat script:* reformat_scripts/obs/reformat_obs_esacci_oc.py


References
----------

* Sathyendranath, S., et al. (2019), An ocean-colour time series for use in climate studies: the experience of the Ocean-Colour Climate Change Initiative (OC-CCI). Sensors: 19, 4285. doi:10.3390/s19194285.
* ESACCI-OC dataset: http://dx.doi.org/10.5285/00b5fc99f9384782976a4453b0148f49

Example plots
-------------

.. _fig_ocdiag_maps:
.. figure::  /recipes/figures/ocean/model_vs_obs_MassConcentrationofTotalPhytoplanktonExpressedasChlorophyllinSeaWater_NorESM2-LM_ESACCI-OC__maps.png
   :align:   center
   :width:   12cm

   Surface chlorophyll from ESACCI-OC ocean colour data version 5.0 and the
   CMIP6 model NorESM2-LM. This model overestimates chlorophyll compared to
   the observations.

.. _fig_ocdiag_scatter:
.. figure::  /recipes/figures/ocean/model_vs_obs_MassConcentrationofTotalPhytoplanktonExpressedasChlorophyllinSeaWater_NorESM2-LM_ESACCI-OC__scatter.png
   :align:   center
   :width:   8cm

   Scatter plot of surface chlorophyll from ESACCI-OC ocean colour data
   version 5.0 and the CMIP6 model NorESM2-LM.