bug in wind forcing for lagrangian iceberg model

[davestorkey]

Context

The icebergs are steered using the 10m atmospheric winds, the sea ice velocities and the ocean surface currents. It is actually the wind stresses that are passed to the ICB module and these are converted to 10m winds using a uniform drag coefficient in these lines in icb_utl_interp:

      pua  = icb_utl_bilin_h( ua_e, pi, pj, 'U', .true.   )    ! 10m wind
      pva  = icb_utl_bilin_h( va_e, pi, pj, 'V', .true.   )    ! here (ua,va) are stress => rough conversion from stress to speed
      zcd  = 1.22_wp * 1.5e-3_wp                               ! air density * drag coefficient 
      zmod = 1._wp / MAX(  1.e-20, SQRT(  zcd * SQRT( pua*pua + pva*pva)  )  )
      pua  = pua * zmod                                       ! note: stress module=0 necessarly implies ua=va=0
      pva  = pva * zmod

However, the wind stresses are passed to ICB after they have been modified by the sea ice, so where there is sea ice (utau,vtau) are the ice-ocean stresses rather than the wind stresses, which is inconsistent with the above code.

Fix

I propose to save (utau,vtau) before the sea ice modifies them and pass these to the ICB module.

Note that a better fix would be to pass the 10m winds rather than the wind stresses to the ICB module, but this is a lot more coding especially in the context of atmosphere-ocean coupled models where we would need to pass the 10m winds from the atmosphere via the coupler.

[davestorkey]

In 15341:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

In 15367:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

In 15369:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

In 15372:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

Now fixed in 4.0-HEAD and trunk.