Opened 6 years ago

Closed 6 years ago

#157 closed defect (fixed)

The 'beta' factor in enerbil during coupling with LMDZ

Reported by: fwang Owned by: somebody
Priority: major Milestone:
Component: Physical processes Version: trunc
Keywords: beta, enerbil, couple Cc:

Description (last modified by jgipsl)

  1. Problem:

The derivation of the surface temperature as it is done in ORCHIDEE-TRUNK is not consistent with surface energy budget equation for implicit coupling with the vertical diffusion in the boundary layer.
In the trunk of ORCHIDEE, the stress factor beta is missing in the denominator in the sensitivity of the latent heat flux to the surface temperature at the old time step. This is coded in enerbil as:

larsub_old = chalsu0 * vbeta1 * (un - vbeta5) * (peqBcoef - qsol_sat) / (zikq - peqAcoef)


lareva_old = chalev0 * (un - vbeta1(ji)) * (un - vbeta5(ji)) * vbeta(ji) * &
           & (peqBcoef(ji) -  valpha(ji) * qsol_sat(ji)) / (zikq - peqAcoef(ji)) &
           & + chalev0 * vbeta5(ji) * (peqBcoef(ji) - qsol_sat(ji)) / (zikq - peqAcoef(ji))

larsub_sns = chalsu0 * vbeta1(ji) * (un - vbeta5(ji)) * zicp(ji) * pdqsold(ji) / (zikq - peqAcoef(ji))

lareva_sns = chalev0 * ((un - vbeta1(ji))*(un - vbeta5(ji)) * vbeta(ji) * valpha(ji) + vbeta5(ji)) * &
           & zicp(ji) * pdqsold(ji) / (zikq - peqAcoef(ji))

This is not consistent with a fully implicit surface energy budget equation and could lead to energy conservation problem.

  1. Action decided

It has been decided to re-introduce the beta and take the following formulation for the ORCHIDEE-TRUNK:

larsub_old = chalsu0 * vbeta1 * (un - vbeta5) * (peqBcoef - qsol_sat) / (zikq - vbeta1 * (un - vbeta5) * peqAcoef)

lareva_old = chalev0 * (un - vbeta1(ji)) * (un - vbeta5(ji)) * vbeta(ji) * &
           & (peqBcoef(ji) -  valpha(ji) * qsol_sat(ji)) / (zikq - (un - vbeta1(ji)) * (un - vbeta5(ji)) * vbeta(ji) * peqAcoef(ji)) &
           & + chalev0 * vbeta5(ji) * (peqBcoef(ji) - qsol_sat(ji)) / (zikq - vbeta5(ji) * peqAcoef(ji))

larsub_sns = chalsu0 * vbeta1(ji) * (un - vbeta5(ji)) * zicp(ji) * pdqsold(ji) / (zikq - vbeta1(ji) * (un - vbeta5(ji)) * peqAcoef(ji))

lareva_sns = chalev0 * ((un - vbeta1(ji))*(un - vbeta5(ji)) * vbeta(ji) * valpha(ji) + vbeta5(ji)) * &
           & zicp(ji) * pdqsold(ji) / (zikq - ((un - vbeta1(ji))*(un - vbeta5(ji)) * vbeta(ji) * valpha(ji) + vbeta5(ji))* peqAcoef(ji))

Note that the correction does not change significantly the results of ORC-LMDZ simulations.

  1. Complementary notes

The current formulation can be seen as a mix between an implicit scheme for net radiation, H, potential ET (ETP), and an explicit scheme for beta. This has been introduced by Jan to support the implementation of a new energy budget based on a Penmann-Monteith ETP. But introducing the virtual temperature of a wet surface (the hypothetically wet temperature of Milly, 1992), further noted T* could be implemented in the standard implicit equations. The above change could also be reverted when the new energy budget will be implemented (which is not yet the case). Both option can be explored once we are ready to change the ETP formulation.

Change History (2)

comment:1 Changed 6 years ago by jgipsl

  • Description modified (diff)

comment:2 Changed 6 years ago by jgipsl

  • Resolution set to fixed
  • Status changed from new to closed

Done in rev [2425]

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