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Southern Ocean cloud biases in ACCESS and improvements

Southern Ocean cloud biases in ACCESS and improvements. www.cawcr.gov.au. Charmaine Franklin 27 November 2012. satellite simulators. Diagnosing cloud processes in climate models with observations is difficult and fraught with issues

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Southern Ocean cloud biases in ACCESS and improvements

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  1. Southern Ocean cloud biases in ACCESS and improvements www.cawcr.gov.au Charmaine Franklin 27 November 2012

  2. satellite simulators • Diagnosing cloud processes in climate models with observations is difficult and fraught with issues – Correspondence of model quantities to available observations – Limitations of satellite observations – Scale of model grids (~100 km) vs. satellite pixels (~1 km) • Simulators reduce the effects of these issues so that comparisons between models and observations more likely are an evaluation of the model • The simulator is a piece of diagnostic code that mimics the observational process by converting model variables into pseudo-satellite observations What would a satellite see if the atmosphere had the clouds of a climate model? The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  3. satellite simulator schematic climate model simulated satellite fields retrieved satellite fields model output fields retrieval algorithm downscaler and forward model satellite simulator retrieval algorithm observed radiances simulated radiances satellite instruments The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  4. ACCESS1.3 AMIP model evaluation The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  5. cloud fraction djf 2006-2007 > 680 hPa 50 – 440 hPa 440 –680 hPa The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  6. cloud fraction jja 2007 The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  7. cloud/hydrometeor occurrence zonal mean The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  8. cloud radiative effect Subtracting the clear sky fluxes from total gives a measure of cloud effects on outgoing radiation: reverse the sign so the effect is into the climate system The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  9. cloud radiative effect error (djf and jja 2007) The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  10. southern ocean djf2007 40 – 60S, 130 – 175W The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  11. southern ocean The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  12. model developments: ice fall speeds • Franklin et al. (2012) identified that PC2 produces large in-cloud water contents and faster falling ice particles in mid-lower levels • ACCESS climate set up uses 1 ice prognostic but this is split diagnostically by temperature to represent 2 hydrometeor types: small ice crystals and large aggregates - snow The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  13. The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  14. integrated histograms The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  15. cloud radiative effect The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  16. summary ACCESS1.3 SO evaluation: • total cloud cover underestimated by up to 20% • low -8%, mid -12%, high +2% • SW and net cloud radiative effect underestimated in djf by 18 Wm-2 • High clouds: Good comparison with CloudSat cloud fraction with but due to too many low radar reflectivities not enough large – ice particle sizes underestimated • Too much high cloud fraction compared to CALIPSO and not enough occurrences of large scattering ratios – ice water content underestimated • Low clouds < 2 km: not enough condensate and non-precipitating cloud, too much rain and drizzle • ISCCP: Not enough optically thick clouds at all heights • Changing ice fall speeds shows some improvements: increases frequency of occurrence of large SR and optically thick clouds, particularly at correct height The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

  17. The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Charmaine Franklin Email: charmaine.franklin@csiro.au Web: www.cawcr.gov.au Thank you www.cawcr.gov.au

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