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Subsections

# 7 Data Exchanged with Component Models

```Each component model exchanges data with the Coupler only. Component models have
no direct connection with each other -- all data is routed through the Coupler.
Most data is in the form of 2D fields.  This data is accompanied by certain
timing and control information (arrays of scalar real or integer values), such
as the current simulation data and time.
```

## 7.1 Units Convention

```All data exchanged conforms to this units convention:

o Sign convention:
positive value <=> downward flux
o Unit convention:
temperature   ~ Kelvin
salt          ~ g/kg
velocity      ~ m/s
pressure      ~ N/m^2 = Pa
humidity      ~ kg/kg
air density   ~ kg/m^3
momentum flux ~ N/m^2
heat flux     ~ W/m^2
water flux    ~ (kg/s)/m^2
salt flux     ~ (kg/s)/m^2
coordinates   ~ degrees north or east
domain mask   ~ 0 <=> an inactive grid cell
```

## 7.2 Time Invariant Data

```This section provides a list of the time invariant data exchanged between the
Coupler and each component model.  Generally this data is the "domain" data:
coordinate arrays, domain mask, cell areas, etc.  It is assumed that the
domain of all models is represented by a 2D array (although not necessarily a
latitude/longitude grid).

Data sent to Coupler

domain data
* grid cell's center coordinates, zonal      (degrees north)
* grid cell's center coordinates, meridional (degrees east)
* grid cell's four vertex coordinates, zonal      (degrees north)
* grid cell's four vertex coordinates, meridional (degrees east)
* grid cell area (radians squared)
* grid cell domain mask ( 0 <=> not in active domain)
* ni,nj: the dimensions of the underlying 2D array data structure

time coordination data
* ncpl: number of times per day the component will communicate (exchange
data) with the Coupler.

other information
* IC flag: indicates whether the Coupler should use model IC's contained
on the Coupler's restart file or IC's in the initial message sent from
the component model.

Data sent to Component Models

time coordination data
* date, seconds: the exact time the Coupler will start the simulation from.
```

## 7.3 Time Variant Data

```This section provides a list of the time-evolving data sent exchanged between
the Coupler and each component model. Generally this is state, flux, and
diagnostic quantities.

Each component model provides the Coupler with a set of output fields.
Output fields from a model include output states (which can be used by another
component to compute fluxes) and output fluxes (fluxes that were computed within
the model and which need to be exchanged with another component model.

The Coupler provides each component model with input fields. Input fields
sent to a model include input states (the state variables of other models,
which are needed to do a flux calculation) and input fluxes (a forcing fields
computed by some other component).

Flux fields sent to or from the Coupler are understood to apply over the
communication interval beginning when the data was received and ending when the
next message is received.  The component models must insure that fluxes sent to
the Coupler are computed with this in mind -- failure to do so may result in the
non-conservation of fluxes.  For example, if the atmosphere component
communicates with the Coupler once per hour, but takes three internal time steps
per hour, then the precipitation (water flux) sent to the Coupler should be the
average precipitation over an hour (the average precipitation over three
internal time steps).  Similarly, if the ocean component has a communication
interval of one day, but takes 50 internal time steps per day, then the
precipitation flux field it receives from the Coupler should be applied as
ocean boundary condition forcing for all 50 time steps during the next
communication interval.
```

### 7.3.1 Atmosphere Model

```Data sent to Coupler

states
* layer height (m)
* zonal      velocity (m/s)
* meridional velocity (m/s)
* temperature (Kelvin)
* potential temperature (Kelvin)
* pressure (Pa)
* equivalent sea level pressure (Pa)
* specific humidity (kg/kg)
* density humidity (kg/m^3)

fluxes
* precipitation: liquid, convective  ((kg/s)/m^2)
* precipitation: liquid, large-scale ((kg/s)/m^2)
* precipitation: frozen, convective  ((kg/s)/m^2)
* precipitation: frozen, large-scale ((kg/s)/m^2)
* shortwave radiation: downward, visible      , direct  (W/m^2)
* shortwave radiation: downward, near-infrared, direct  (W/m^2)
* shortwave radiation: downward, visible      , diffuse (W/m^2)
* shortwave radiation: downward, near-infrared, diffuse (W/m^2)

diagnostic quantities

states
* albedo: visible      , direct
* albedo: near-infrared, direct
* albedo: visible      , diffuse
* albedo: near-infrared, diffuse
* surface temperature (Kelvin)
* snow height (m)
* ice   fraction
* ocean fraction
* land  fraction  (implied by ice and ocean fractions)

fluxes
* zonal      surface stress (N/m^2)
* meridional surface stress (N/m^2)
* latent heat   (W/m^2)
* sensible heat (W/m^2)
* evaporation ((kg/s)/m^2)

diagnostic quantities
* 2 meter reference air temperature (Kelvin)
```

### 7.3.2 Ice Model

```Data sent to Coupler

states
* ice fraction
* surface temperature (Kelvin)
* albedo: visible      , direct
* albedo: near-infrared, direct
* albedo: visible      , diffuse
* albedo: near-infrared, diffuse

fluxes
* atm/ice: zonal      surface stress (N/m^2)
* atm/ice: meridional surface stress (N/m^2)
* atm/ice: latent heat                (W/m^2)
* atm/ice: sensible heat              (W/m^2)
* atm/ice: longwave radiation, upward (W/m^2)
* atm/ice: evaporation ((kg/s)/m^2)
* ice/ocn: penetrating shortwave radiation (W/m^2)
* ice/ocn: ocean heat used for melting (W/m^2)
* ice/ocn: melt water ((kg/s)/m^2)
* ice/ocn: salt flux  ((kg/s)/m^2)
* ice/ocn: zonal      surface stress (N/m^2)
* ice/ocn: meridional surface stress (N/m^2)

diagnostic quantities
* 2 meter reference air temperature (Kelvin)

states
* ocn: temperature (Kelvin)
* ocn: salinity    (g/kg)
* ocn: zonal      velocity (m/s)
* ocn: meridional velocity (m/s)
* atm: layer height (m)
* atm: zonal      velocity (m/s)
* atm: meridional velocity (m/s)
* atm: potential temperature (Kelvin)
* atm: temperature           (Kelvin)
* atm: specific humidity (kg/kg)
* atm: density (kg/m^3)

fluxes
* ocn: dh/dx: zonal      surface slope (m/m)
* ocn: dh/dy: meridional surface slope (m/m)
* ocn: Q>0: heat of fusion    (W/m^2), or
Q<0: melting potential (W/m^2)
* atm: shortwave radiation: downward, visible      , direct  (W/m^2)
* atm: shortwave radiation: downward, near-infrared, direct  (W/m^2)
* atm: shortwave radiation: downward, visible      , diffuse (W/m^2)
* atm: shortwave radiation: downward, near-infrared, diffuse (W/m^2)
* atm: longwave  radiation, downward (W/m^2)
* atm: precipitation: liquid ((kg/s)/m^2)
* atm: precipitation: frozen ((kg/s)/m^2)
```

### 7.3.3 Land Model

```Data sent to Coupler

states
* surface temperature (Kelvin)
* albedo: visible      , direct
* albedo: near-infrared, direct
* albedo: visible      , diffuse
* albedo: near-infrared, diffuse
* snow depth (m)

fluxes
* zonal      surface stress  (N/m^2)
* meridional surface stress  (N/m^2)
* latent heat                (W/m^2)
* sensible heat              (W/m^2)
* evaporation    ((kg/s)/m^2)
* coastal runoff ((kg/s)/m^2)

diagnostic quantities
* 2 meter reference air temperature (Kelvin)

states
* atm layer height (m)
* atm zonal      velocity (m/s)
* atm meridional velocity (m/s)
* atm potential temperature (Kelvin)
* atm specific humidity (kg/kg)
* atm pressure (Pa)
* atm temperature (Kelvin)

fluxes
* precipitation: liquid, convective  ((kg/s)/m^2)
* precipitation: liquid, large-scale ((kg/s)/m^2)
* precipitation: frozen, convective  ((kg/s)/m^2)
* precipitation: frozen, large-scale ((kg/s)/m^2)
* shortwave radiation: downward, visible      , direct  (W/m^2)
* shortwave radiation: downward, near-infrared, direct  (W/m^2)
* shortwave radiation: downward, visible      , diffuse (W/m^2)
* shortwave radiation: downward, near-infrared, diffuse (W/m^2)
```

### 7.3.4 Ocean Model

```Data sent to Coupler

states
* surface temperature (Kelvin)
* salinity (g/kg)
* zonal      velocity (m/s)
* meridional velocity (m/s)

fluxes
* dh/dx: zonal      surface slope (m/m)
* dh/dy: meridional surface slope (m/m)
* Q>0: heat of fusion    (W/m^2), or
Q<0: melting potential (W/m^2)

states
* equivalent sea level pressure (Pa)
* ice fraction

fluxes
* zonal      surface stress (N/m^2)
* meridional surface stress (N/m^2)
* latent heat                  (W/m^2)  (note: derived from evaporation)
* sensible heat                (W/m^2)