.. _icon_model_control:

Control Simulation
##################

The ICON control simulation covers 20 years in total (1990–2009) and is used to assess whether the coupled system starts close to equilibrium. Both the atmosphere and ocean use a horizontal grid resolution of 5 km (public ICON grid id: R02B09).

+----------+------------------------------------+--------------+-------------+-------------------------------------------------+-----------------------------------+
| Model    | Spatial Resolution                 | Time         | Realization | Experiment ID                                   | DestinE Data Lake (bridge site)   |
+==========+====================================+==============+=============+=================================================+===================================+
| ICON     | 5km atmosphere; 5km ocean          |   1990-2009  | 1          |  climatedt-gen2-icon-baseline-cont-5km-r1       | LUMI data bridge                  |
+----------+------------------------------------+--------------+-------------+-------------------------------------------------+-----------------------------------+

Forcing data
------------

In this control simulation, global mean concentrations of greenhouse gases, ozone, and aerosols are fixed at 1990 levels.

The ocean initial state (1990-01-01) is taken from a spun-up ocean model run with climatological forcing, as described in :ref:`icon_initial_conditions_and_forcing`. The atmosphere, solid moisture, snow cover, and soil and surface temperature are derived from ECMWF operational analyses without additional spin-up for the chosen start date and are interpolated onto the horizontal grid during pre-processing.


.. Assessment of the Control Simulation
.. ------------------------------------

.. Gregory Plot
.. ^^^^^^^^^^^^

.. The Gregory plot (:numref:`c1`) shows the co-evolution of global mean 2 m air temperature and net top-of-atmosphere (TOA) radiation over the control period. In 1990, ERA5 has a global mean temperature of 14.24°C, while ICON is colder by ~0.6°C and exhibits a negative TOA imbalance of approximately −0.59 W m\ :sup:`-2`, indicating an adjustment of the ocean spin-up to the atmosphere. In subsequent years, ICON remains colder than ERA5, with the cold bias increasing to about 0.8°C. At the same time, the TOA imbalance becomes positive and falls within the CERES observational range, indicating rapid atmospheric adjustment. The persistence of the cold bias suggests that the coupled system has not reached equilibrium within the 10-year simulation period, though with a slight tendency towards equilibrium.

.. .. _c1:
.. .. figure:: ../../../../evaluation/mn5/figures/Tco2559_Control_Gregory_ICON.png
..    :align: center
..    :width: 100%

..    Gregory plot for ICON, where each year has a different color, along side with observational reference data of ERA5 for 2m temperature for the year 1990 and CERES for net radiation at TOA from 2001-01-01 to 2020-12-31.

.. Ocean drift from the spin-up
.. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. :numref:`c2` displays a Hovmöller diagram of the global mean temperature anomalies of the 3D structure of the ocean.  
.. The cold bias development of ICON is clearly observed with impact in the uppermost layer of the ocean, between 0-100 m, with a strong seasonal cycle.
.. In the uppermost layer, the cold bias anomalies intensify up to 1997, with a later reduction in bias by the end of the simulation, with negative values between 0.4 and 0.5.
.. Thus, the uppermost layer seems to develops a trend towards equilibrium, but is still far from it.

.. Below the uppermost layer of the ocean, ICON displays a systematic anomaly warm bias between 100 and 200 m depth. 
.. This bias is likely a response of the ocean to its heat distribution from the surface through deepening of the thermocline or enhanced vertical mixing during the adjustment of the spin-up time. 
.. Deeper levels remain largely stable with near-zero anomalies.

.. .. _c2:
.. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_temperature_anomalies_control.png
..    :align: center
..    :width: 100%

..    Time-depth (monthly mean) Hovmöller diagram of global mean ocean temperature anomalies (K) relative to the initial state in ICON control simulation. 


.. Salinity anomalies (:numref:`c3`) show a complementary vertical structure to the temperature drift of the ocean. 
.. In the uppermost levels, ICON displays a reduction in salinity, indicating a refreshing due to increased precipitation (to be discussed in :ref:`icon-control_regional_bias`). 
.. Below this, at depths between 100 and 200 m, a salinification signal is quite evident, penetrating deeper with time. 
.. This pattern indicates an adjustment of the haline stratification during the spin-up time. Similar to temperature, the deeper parts of the ocean do not show significant changes and remain unaffected.

.. .. _c3:
.. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_salinity_anomalies_control.png
..    :align: center
..    :width: 100%

..    Time-depth (monthly mean) Hovmöller diagram of global mean ocean salinity anomalies (PSU) relative to the initial state of ICON control simulation

.. .. _icon-control_regional_bias:

.. Regional bias
.. ^^^^^^^^^^^^^

.. Overall, ICON displays an increase in precipitation globally with respect to MSWEP, going from 0.32 mm d\ :sup:`-1` towards 0.25 mm d\ :sup:`-1`. 
.. :numref:`c4` displays the regional precipitation bias using the two-year mean, initial (1990-1991), middle (1994-1995) and last year (1999-2000). 
.. In the equatorial Pacific basin, ICON displays a negative precipitation bias, which becomes stronger at the end of the simulation, especially near the warm pool. 
.. Over land, ICON shows an overall increase in precipitation, except in the Amazon forest, which can be explained by a shift of the inter-tropical convergence zone in the Atlantic. 
.. The maritime continent shows the strongest persistent positive bias of precipitation.

.. .. _c4:
.. .. figure:: ../../../../evaluation/levante/Fig/ICON_bias_pr_control.png
..    :align: center
..    :width: 100%

..    Comparison of precipitation bias of ICON with respect of MSWEP (1990) of the first (left) and last (right) two years

.. :numref:`c5` encompasses and can explain part of the precipitation bias in ICON. 
.. In the Pacific, a strong cold tongue develops from the start of the simulations, which reaches a maximum reduction of temperature in the order of 4°C at the last period of the simulation. 
.. The strong cold bias in the Pacific, Africa, and the western coastline of the USA is compensated by a warm bias in the midlatitudes over land and the southern ocean.  

.. .. _c5:
.. .. figure:: ../../../../evaluation/levante/Fig/ICON_bias_2t_control.png
..    :align: center
..    :width: 100%
   
..    Comparisson of surface temperature bias of ICON with respect of ERA5 (1990) of the first (left) and last (right) two years