2.2 Information Exchanged with the Coupler

When CSIM5 is run coupled, it sends and receives forcing information from the other components via a flux coupler. Message passing between the ice model and the coupler is accomplished using MPI. Fluxes computed within the ice model and used by other components are sent to the flux coupler for distribution. Although CSIM5 contains an ice thickness distribution in each grid cell, and the ice state variables and fluxes depend on the ice thickness, only aggregate quantities of each grid cell are passed to the coupler.

The coupler requires that the fluxes it receives from the ice model be divided by the total ice area in each grid cell, since the coupler multiplies these fluxes by the ice area. This is done in subroutine scale_fluxes just before the call to to_coupler. These fluxes have units of "per unit ice area".

The forcing information received by the ice model from the coupler at the top of the timestep is listed in Table 1. By convention, directional fluxes are positive downward. The symbols in the first column correspond to those in the equations found in the Scientific Description document. These are the forcing variables required by the ice model for running coupled or uncoupled. The information calculated by the ice model and sent to the coupler at mid-timestep is listed in Table 2.

Table 1: Fluxes and state variables received by the sea ice model from the coupler

Symbol	Variable Name	Description	Units
		Atmospheric Variables
$z_a$	zlvl	Reference height	m
$u_a$	uatm	Zonal wind speed at $z_a$	m s$^{-1}$
$v_a$	vatm	Meridional wind speed at $z_a$	m s$^{-1}$
$\theta_a$	potT	Potential temperature at $z_a$	K
$T_a$	Tair	Air temperature at $z_a$	K
$q_a$	Qa	Specific humidity at $z_a$	kg kg$^{-1}$
$\rho_a$	rhoa	Air density at $z_a$	kg m$^{-3}$
	Atmosphere $\Rightarrow$ ice fluxes
$F_{SWvdr}$	swvdr	Direct, visible downwelling shortwave	W m$^{-2}$
$F_{SWvdf}$	swvdf	Diffuse, visible downwelling shortwave	W m$^{-2}$
$F_{SWndr}$	swidr	Direct, near infrared downwelling shortwave	W m$^{-2}$
$F_{SWndf}$	swidf	Diffuse, near infrared downwelling shortwave	W m$^{-2}$
$F_{LWDN}$	flw	Downwelling longwave	W m$^{-2}$
$F_{RN}$	frain	Freshwater flux due to rain	kg m$^{-2}$ s$^{-1}$
$F_{SNW}$	fsnow	Freshwater flux due to snow (liquid)	kg m$^{-2}$ s$^{-1}$
	Ocean Variables
$T_o$	sst	Sea surface temperature	K
$S_o$	sss	Sea surface salinity	ppt
$u_o$	uocn	Surface ocean current	m s$^{-1}$
$v_o$	vocn	Surface ocean current	m s$^{-1}$
$H_{ox}$	ss_tltx	Sea surface slope	m m$^{-1}$
$H_{oy}$	ss_tlty	Sea surface slope	m m$^{-1}$
	Ocean $\Rightarrow$ ice fluxes
$F_{Qoi}$	frzmlt	Freezing/melting potential	W m$^{-2}$

Table 2: Fluxes and state variables sent from sea ice model to coupler

Symbol	Variable Name	Description	Units
$T_{ref}$	Tref	Atmospheric reference temperature (2 m)	K
$Q_{ref}$	Qref	Atmospheric specific humidity (2 m)	kg kg$^{-1}$
		Ice Variables
$A$	ailohi	Ice concentration
$T_s$	Tsfc	Surface temperature	K
$\alpha_{vdr}$	alvdr	Albedo (visible, direct)
$\alpha_{ndr}$	alidr	Albedo (near infrared, direct)
$\alpha_{vdf}$	alvdf	Albedo (visible, diffuse)
$\alpha_{ndf}$	alidf	Albedo (near infrared, diffuse)
	Ice $\Rightarrow$ atmosphere fluxes
$F_{LH}$	flat	Latent heat flux	W m$^{-2}$
$F_{SH}$	fsens	Sensible heat flux	W m$^{-2}$
$F_{LWUP}$	flwout	Upwelling longwave	W m$^{-2}$
$F_{EVAP}$	evap	Evaporated water	kg m$^{-2}$ s$^{-1}$
$\tau_{ax}$	tauxa	Atmosphere-ice stress, zonal	N m$^{-2}$
$\tau_{ay}$	tauya	Atmosphere-ice stress, meridional	N m$^{-2}$
	Ice $\Rightarrow$ ocean fluxes
$F_{SWo}$	fswthru	Shortwave transmitted to ocean	W m$^{-2}$
$F_{Qio}$	fhnet	Net heat flux to ocean	W m$^{-2}$
$F_{Wo}$	fresh	Fresh water flux	kg m$^{-2}$ s$^{-1}$
$F_{Sa}$	fsalt	Salt flux	kg m$^{-2}$ s$^{-1}$
$\tau_{ox}$	tauxo	Ice-ocean stress, zonal	N m$^{-2}$
$\tau_{oy}$	tauyo	Ice-ocean stress, meridional	N m$^{-2}$