southern ocean cloud biases in access and improvements
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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 - PowerPoint PPT PresentationTRANSCRIPT
The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology
Southern Ocean cloud biases in ACCESS and improvements
Charmaine Franklin
27 November 2012
www.cawcr.gov.au
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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 Research A partnership between CSIRO and the Bureau of Meteorology
satellite simulator schematic
model output fields
observed radiances
simulated radiances
retrieval algorithm
retrieval algorithm
retrieved satellite fields
downscaler and forward model
simulated satellite fields
satellite simulator
climate model
satellite instruments
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
ACCESS1.3 AMIP model evaluation
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
cloud fraction djf 2006-2007
50 – 440 hPa 440 –680 hPa > 680 hPa
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
cloud fraction jja 2007
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
cloud/hydrometeor occurrence zonal mean
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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 Research A partnership between CSIRO and the Bureau of Meteorology
cloud radiative effect error (djf and jja 2007)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
southern ocean djf200740 – 60S, 130 – 175W
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
southern ocean
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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 Research A partnership between CSIRO and the Bureau of Meteorology
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
integrated histograms
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
cloud radiative effect
djf SW (rmse, bias) LW (rmse, bias) net (rmse, bias)
global ctl 23.5, 4.8 12.9, -0.3 20.2, 4.5
global fall 22.7, 5.0 12.4, -1.0 19.6, 4.0
SO ctl 24.7, 17.9 14.3, 0.5 20.0, 18.3
SO fall 23.4, 16.3 13.7, 0.1 18.9, 16.7
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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
Charmaine Franklin
Email: [email protected]: www.cawcr.gov.au
Thank youwww.cawcr.gov.au