Opened 9 years ago

Last modified 15 months ago

#29 assigned enhancement

Parameters values : z0_over_height, height_displacement, ct_karman

Reported by: dsolyga Owned by: fcheruy
Priority: minor Milestone: Not scheduled yet
Component: Physical processes Version: trunc
Keywords: cleaning, constantes Cc:

Description

Jan suggested to modify the following parameters values :

  • z0_over_height : from 0.0625 to 0.046
  • height_displacement : from 0.75 to 0.67
  • ct_karman : from 0.35 to 0.40

To note: z0_over_height and height_displacement are externalized, so if needed these parameters can be reset before validation.
See Branches/MergeHydro/logz0_note.

Tests

Sensitivity tests need to be done for evaluation and validation (off-line/coupled).

Change History (8)

comment:1 in reply to: ↑ description Changed 9 years ago by aducharne

ct_karman is the von Karman constant, established from turbulence similarity analysis.
Its value is usually assumed to close to 0.4, and often set to 0.41

Note that increasing ct_karman will decrease the aerodynamic resistance, thus increase evapotranspiration (ET). It might be a good thing since ET is smaller in ORCHIDEE than in other LSMs in intercomparison projects. It could also help reducing the warm bias over land in teh extra-tropics.

Replying to dsolyga:

Jan suggested to modify the following parameters values :

  • z0_over_height : from 0.0625 to 0.046
  • height_displacement : from 0.75 to 0.67
  • ct_karman : from 0.35 to 0.40

To note: z0_over_height and height_displacement are externalized, so if needed these parameters can be reset before validation.
See Branches/MergeHydro/logz0_note.

Tests

Sensitivity tests need to be done for evaluation and validation (off-line/coupled).

comment:2 Changed 8 years ago by peylin

  • Owner changed from somebody to jpolcher
  • Status changed from new to assigned

comment:3 Changed 4 years ago by jgipsl

height_displacement and ct_karma were changed in revision [3524]. They are now:

height_displacement = 0.66 
ct_karman = 0.41

In the same commit, z0_over_height were extened to be dependent of the pft. It is now:

  REAL(r_std), PARAMETER, DIMENSION(nvmc) :: z0_over_height_mtc = &   ! Factor to calculate roughness height from 
  & (/  0.0, 0.0625, 0.0625, 0.0625, 0.0625, 0.0625, 0.0625,  &       !! vegetation height (unitless)   
  &  0.0625, 0.0625, 0.0625, 0.0625, 0.0625, 0.0625  /)

comment:4 Changed 4 years ago by jgipsl

z0_over_height is only used in subroutine condveg_z0cdrag which is only called when rough_dyn=false.

comment:5 Changed 4 years ago by jgipsl

  • Cc jpolcher removed
  • Milestone changed from ORCHIDEE 2.0 to ORCHIDEE 3.0
  • Owner changed from jpolcher to fcheruy
  • Version changed from orchidee_1_9_6 to trunc

comment:6 Changed 17 months ago by fcheruy

For now the default for the computation of the roughness lengths is rough_dyn=y and these values are not used. The request could be reconsidered if the default is changed in Orchidee.
The Von Karman constant has been updated already. However in LMDZ it is set to 0.40, I suggest to do the same in Orchidee.

comment:7 Changed 17 months ago by jgipsl

  • Milestone changed from ORCHIDEE 3.0 to ORCHIDEE 4.0

Decided during ORCH meeting today:

  • Frederique has done simulations with Ionela Musat. She'll add more information in this ticket.
  • for short terme: a patch to be done in LMDZ so that q2m never becomes negative
  • for longer terme: Nicolas Vuichard would like to look into ROUGH_DYN parametrization to see what can be done. For this part, the ticket is changed to milestone 4.0

comment:8 Changed 15 months ago by luyssaert

  • Milestone changed from ORCHIDEE 4.0 to Not scheduled yet
Note: See TracTickets for help on using tickets.