15 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.

15.1 Units Convention

All data exchanged conforms to the following sign convention:

$\fbox{positive value $\Longleftrightarrow$\ downward flux}$

And these unit conventions:

temperature
salinity
velocity
pressure
humidity
air density
momentum flux
heat flux
water flux
salt flux
coordinates: degrees north or east
area
domain mask: $0 \Longleftrightarrow$ an inactive grid cell

15.2 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).

15.2.1 Data sent to Coupler

domain data

grid cell's center coordinates, zonal (degrees north)
grid cell's center coordinates, meridional (degrees east)
grid cell area (radians squared)
grid cell domain mask ( 0 $\Longleftrightarrow$ 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.

15.2.2 Data sent to Component Models

time coordination data

date, seconds: the exact time the Coupler will start the simulation from.

15.3 Time Variant Data

This section provides a list of the time-evolving data sent exchanged between the Coupler and each component model. This list is also contained in the cpl_fields_mod module in cpl6. Generally a quantity is a state or a flux. Some state variables are used only as diagnostics and are denoted with a *.

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 received 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.