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SUMMARY:Diagnosing potential causes of the HADGEM3 Southern Ocean warm sea
  surface temperature bias - Dr Pat Hyder\, Ocean Modelling Evaluation and 
 Development Met Office
DTSTART:20120911T090000Z
DTEND:20120911T100000Z
UID:TALK39706@talks.cam.ac.uk
CONTACT:Dr Andrew Meijers
DESCRIPTION:The Southern Ocean is a critically important region for global
  climate for many reasons\, including its key roles in determining the rat
 e of transient climate change\; forming/transforming many of the major int
 ermediate and deep water masses\; influencing sea level change\; etc.\nIt 
 is also a region of low thermal stratification which is marginally stable 
 mainly due haline stratification. Erroneous thermal stratification in clim
 ate models would therefore be expected to have a substantial impact on the
  simulated density stratification\, limiting the accuracy of simulated upt
 akes of heat and carbon.\n\nThe Southern Ocean sea surface temperature (SS
 T) biases in HADGEM3 are summarised\, together with those documented for I
 PCC models.  The many processes influencing sea surface temperature and ex
 pected errors in their representation in climate models\, particularly HAD
 GEM3\, are also discussed.  We then attempt to systematically diagnose pot
 ential causes of the HADGEM3 SST biases.  First we compare relevant parame
 ters of the\ncoupled HADGEM3 runs with those from equivalent forced runs\,
  which employ DRAKKAR optmised ocean forcing and have much reduced SST bia
 ses. Compared to observational estimates there appear to be significant bi
 ases in the wind stress\, the wind curl and the downwelling short wave in 
 the regions which the SST biases are largest.  Next we present coupled HAD
 GEM3 perturbation experiments which include forcing the ocean using the ti
 me-varying DRAKKAR winds\; increasing/decreasing the downwelling short wav
 e to the ocean\; varying the ocean lateral isopycnal mixing coefficient\; 
 and changing the configuration of the ocean vertical mixing parameterisati
 on.  We find that using DRAKKAR time varying winds and reduced downwelling
  short wave appear to reduce the SST biases. However\, we also find that t
 he SST biases are also affected by both the ocean lateral isopycnal mixing
  coefficient and configuration of the\nocean vertical mixing parameterisat
 ion.\n\nThe reduced SST biases in forced ocean experiments together with t
 he errors identified in the coupled winds and downwelling short wave sugge
 st that errors in the atmospheric model could contribute to causing SST bi
 ases.  However\, the SST biases are also affected by changes to ocean mode
 l configuration.  Further  experiments and analyses are in progress to hel
 p to better understand the HADGEM3 Southern Ocean sea\nsurface temperature
  biases.
LOCATION:British Antarctic Survey\, conference room
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