1. © Crown copyright Met Office Southern Ocean surface flux biases in GCMs Keith Williams, Alejandro Bodas-Salcedo & Patrick Hyder SOCRATES workshop 18/03/14

2. © Crown copyright Met Office Why do we care? Coupled NWP Day 3 forecast bias Coupled NWP Day 14 forecast bias 100yr mean bias

3. © Crown copyright Met Office Southern Ocean annual flux biases Total ShortwaveLatent + sensible Longwave Calculated in AMIP simulations using divergence method: TOA radiation - Divergence  Total Surface Flux TOA radiation - Divergence - Surface radiation  Turbulent Surface Flux

4. © Crown copyright Met Office DJF SW biases The peak SW bias is a long way south!

5. © Crown copyright Met Office CMIP5 AMIP: low OSR CERES EBAF ISCCP FD CMIP5/AMIP

6. © Crown copyright Met Office BCC-CSM-1-1MCanAM4 IPSL-CM5A-LRIPSL-CM5A-MRCNRM-CM5HadGEM2-A MPI-ESM-LRMRI-CGCM3IPSL-CM5B-LRMIROC5 AMIP SW flux bias wrt CERES

7. © Crown copyright Met Office Transpose- AMIP case study (VT: 12Z 17 th Jan 2009) T+30 bias in RSW against CERES-FF

8. © Crown copyright Met Office Cloud bias against ISCCP

9. © Crown copyright Met Office Cloud bias against CALIPSO

10. © Crown copyright Met Office T+30 T & q profiles

11. © Crown copyright Met Office Initial T tendencies

12. © Crown copyright Met Office MetUM – GA5 Southern Ocean mean ISCCP histogram Cloud amount reasonable, but cloud albedo too low. Likely candidates: Cloud microphysics issues (most likely in mixed-phase/SLW cloud) – See Kalli Furtado’s talk. Aerosol issues (insufficient sea salt/DMS at cloud level and/or cloud-aerosol interaction issues).

13. © Crown copyright Met Office Summary All GCMs have too strong a radiative contrast between frontal and non-frontal cloud over the Southern Ocean. In many this leads to excess SW reaching the ocean surface which in some leads to a warm SST bias. Causes probably vary between models, but likely to include insufficent vertical resolution, inaccurate representation of the BL, aerosol biases and cloud microphysics issues. SW biases may only be part of the story and turbulent flux biases are also significant. In all cases, a lack of reliable observations is the main obstacle to making progress.

14. © Crown copyright Met Office Observations wish list Surface fluxes: radiative and turbulent. Broadband fluxes from above and below cloud. Detailed cloud and aerosol obs (CCN, bulk water and ice measurements, aerosol concentrations/chemical conc./PSD/optical properties, etc.). Sea state and sea spray measurements (droplet mass/number concentration). Boundary layer profiles (down to the surface) of temperature, wind speed and RH. All at high temporal frequency (incl. diurnal cycle) and over the model bias regions (which are a long way south!). (Consider flights co-incident with satellite passes)

15. © Crown copyright Met Office

16. Ctrl Mod BL ISCCP

17. © Crown copyright Met Office CALIPSO cloud in ISCCP mid-level regime