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SUMMARY:Understanding and reducing Southern Ocean biases in the HadGEM3 co
 upled climate model - Dr Patrick Hyder\, Met Office
DTSTART:20141107T110000Z
DTEND:20141107T120000Z
UID:TALK55506@talks.cam.ac.uk
CONTACT:Dr Andrew Meijers
DESCRIPTION:We summarise a two year integrated assessment of the represent
 ation of Southern Ocean processes\, from the stratosphere to the deep ocea
 n\, in HadGEM3\, in the context of other IPCC models\, focussing on the ai
 r-sea flux errors in atmosphere only runs.  Using a novel net air-sea obse
 rvational flux product we find that for HadGEM3 there is a good correspond
 ence between atmosphere-only air-sea flux errors and coupled heat content 
 errors in the Southern Ocean\, which suggests that atmosphere errors are t
 he primary driver of coupled heat content biases in HadGEM3.  Evidence sug
 gests that these net flux errors are (~50%) due to radiation errors\, main
 ly short wave due to cloud errors\, and (~50%) due to turbulent flux error
 s\, associated with the representation of storms.  Observational evidence 
 suggests that cloud errors are in part due to a lack of super-cooled cloud
  liquid water content\, which is known to be prevalent in polar regions\, 
 in HadGEM3\, and in part due to representation of aerosols.  New aerosol a
 nd mixed-phase cloud schemes reduce the atmosphere only net heat flux bias
  by ~30% and also reduce coupled sea surface temperature biases by ~50%.  
 Clearly ocean transport and mixing errors also contribute to the coupled h
 eat-content and SST biases.  For example\, for the HadGEM3 atmosphere mode
 l\, employing a coupled 1/4 degree eddy permitting ocean model roughly dou
 bles the Southern Ocean SST bias compared to that when using 1 degree para
 meterised eddy ocean model\, apparently due to more initial heat transport
  into the Southern Ocean.  Ocean mixing is also poorly represented in the 
 HadGEM3 NEMO ocean\, giving rise to under-estimation of Southern Ocean mix
 ed layer depths\, which we have plans to address.
LOCATION:British Antarctic Survey\, Room 307
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