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#1088 (CORE sbc modifies public variable wind speed changing it to relative wind) – NEMO

Opened 11 years ago

Closed 8 years ago

#1088 closed Defect (fixed)

CORE sbc modifies public variable wind speed changing it to relative wind

Reported by: vichi Owned by: nemo
Priority: low Milestone:
Component: OCE Version: v3.4
Severity: Keywords:
Cc:

Description

When the CORE surface boundary conditions are applied in sbcblk_core.F90, NEMO computes the wind speed module (variable wndm) by subtracting the ocean current velocities from each component.

      DO jj = 2, jpjm1
         DO ji = fs_2, fs_jpim1   ! vect. opt.
            zwnd_i(ji,jj) = (  sf(jp_wndi)%fnow(ji,jj,1) - 0.5 * ( pu(ji-1,jj  ) + pu(ji,jj) )  )
            zwnd_j(ji,jj) = (  sf(jp_wndj)%fnow(ji,jj,1) - 0.5 * ( pv(ji  ,jj-1) + pv(ji,jj) )  )
         END DO
      END DO
      CALL lbc_lnk( zwnd_i(:,:) , 'T', -1. )
      CALL lbc_lnk( zwnd_j(:,:) , 'T', -1. )
      ! ... scalar wind ( = | U10m - U_oce | ) at T-point (masked)
!CDIR NOVERRCHK
!CDIR COLLAPSE
      wndm(:,:) = SQRT(  zwnd_i(:,:) * zwnd_i(:,:)   &
         &             + zwnd_j(:,:) * zwnd_j(:,:)  ) * tmask(:,:,1)

Therefore, the piston velocity used for air-sea gas exchange in BGC models is not computed using the 10m wind as in Wanninkhof but using the relative wind speed as well!
This may be sensible for computing the momentum transfer, but not when using the empirical formulation of the piston velocity that is derived from measured 10 m wind.
I think users should be aware that variable wndm is changed and does not correspond anymore to the output variable sowndspeed

In my view sbcblk_core should use a local variable zwndm that corresponds to the relative wind, leaving wndm untouched

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Change History (1)

comment:1 Changed 8 years ago by lovato

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

The code of NEMO v3.6 (and trunk) was fixed in MERGE2013 by introducing the parameter rn_vfac in the namelist of CORE bulk formulas (namsbc_core):

   rn_vfac     = 0.        !  multiplicative factor for ocean/ice velocity
                           !  in the calculation of the wind stress (0.=absolute winds or 1.=relative winds)This is set to 0 by default in namelist_ref.

The issue is still present in NEMO V3.4, but this code has become quite obsolete and it will not be updated.

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