The Energy Balance Equation

According to the sign conventions and variable names used by Cupid, the energy balance equation can be expressed as:


   Source when positive              Sink when positive
    
   RNET(JTOT) + DPSTOR   =   QCOND(2) + ECOND(2) + HSOIL + CPHSTR

where we have grouped terms on the basis of whether they represent energy sources or sinks when they assume positive quantities. These terms are defined further below.

Note that the QCOND and ECOND values used here are from layer JZ=2. This corresponds to ???

Definitions

RNET(JTOT)

The net radiation as measured right above the canopy.

RNET(JTOT) = Rdown(JTOT) - Rup(JTOT)

This is the net incoming radiation absorbed by the plant-soil system and therefore a measure of the energy available to do work.

DPSTOR

The net storage of energy in precipitation droplets.

dpstor=precip(ihr)*(4.1876e6)*(tdropi-tirrig)/(1000.*dt)

If droplets cool during their journey to the canopy top (TRODPI > TIRRIG), this is a net input of energy into the system.

QCOND(2)

The net sensible heat flux from the combined soil-canopy system into the atmosphere.

qcond(jz)=akh(jz)*(tn(ihr,jz+1)-tn(ihr,jz))

                        (Tcanopy   -   Tair)

JZ increases downwards, so a negative QCOND(2) means the canopy is colder than the air and there is a net heat flux downwards.

ECOND(2)

The net energy expended in evapotranspiration.

econd(jz)=alam*4.18e-3*ake(jz)*(en(ihr,jz+1)-en(ihr,jz))

HSOIL

The net heat conducted down into the soil.

hsoil=akh(jzsfc+1)*f*(tn(ihr,jzsfc+1)-tn(ihr,jzsfc+2))

CPHSTR

The net increase in heat stored in the canopy.

cphstr=cphstr+qcap(jz) (summed over jz)

qcap(jz)=cp(jz)*(tn(ihr,jz)-tn(ijhrm1,jz))