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.
All data exchanged conforms to this units convention:
Sign convention:
positive value <=> downward flux
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
area ~ radians^2
domain mask ~ 0 <=> an inactive grid cell
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).
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.
time coordination data
* date, seconds: the exact time the coupler will start the simulation from.
This section provides a list of the time-evolving data sent exchanged between the coupler and the data model. Generally this is state, flux, and diagnostic quantities.
Each data 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 data models must insure that fluxes sent to the coupler are appropriate in this context.
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)
* longwave radiation, upward (W/m^2)
* evaporation ((kg/s)/m^2)
diagnostic quantities
* 2 meter reference air temperature (Kelvin)
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)
* longwave radiation, downward (W/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
* net shortwave radiation (W/m^2)
Data from the input data sequence is assumed to be daily average data. This data is linearly interpolated in time to get instantaneous fields, and this data is sent to the coupler. All data sent to the coupler is taken directly from the input data files, with a few exceptions (see below). The datm input data files are in the same format as history files created by CAM3 (normally they are created by CAM3). The derivations below are based on algorithms that the CAM atmosphere model would have used if it were able to put these fields on a CAM history file.
