southern ocean cloud biases in access and improvements

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: charmaine.franklin@csiro.auWeb: www.cawcr.gov.au

Thank youwww.cawcr.gov.au