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Page 3© Crown copyright 2005 Mid-level mean cloud fractions The mid-level cloud fractions are much reduced compared to observations Direct modification of the diagnostic ice cloud fraction to better improve the mid-level cloud fractions, as in HadGAM
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© Crown copyright 2005 Page 1
Damian Wilson, 12th October 2005
Assessment of model performance and potential improvements using CloudNet data
© Crown copyright 2005 Page 2
Summary
CloudNet data has allowed a long period comparison of cloud properties between models and observations
There is a generally good agreement between the models (including the Met Office) and observations, better than is generally thought
However, there are some specific differences which we can address (for the Met Office)
Microphysical information is also available which can guide future parametrization development
© Crown copyright 2005 Page 3
Mid-level mean cloud fractions
The mid-level cloud fractions are much reduced compared to observationsDirect modification of the diagnostic ice cloud
fraction to better improve the mid-level cloud fractions, as in HadGAM
© Crown copyright 2005 Page 4
Low level cloud
The low level cloud peak is at too low an altitudeA boundary layer problem?
The model has a large amount of fog and very low cloud in stable boundary layersPossibly due to inaccuracies in the stable boundary
layer turbulent flux profiles JJA: Downwards, stable
HadGAM
PC2
m
Observations
© Crown copyright 2005 Page 5
Thick liquid water contents
There are not enough of the highest liquid water contentsPossibly from not including the convective cloud.
The representation of liquid water in convection schemes should be investigated
Possibly a poor representation of the drizzle process, with too ready autoconversion
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Supercooled liquid water content
The mesoscale model (and to a lesser extent, the global model) has significantly less supercooled liquid water than the observationsPossible adjustment of the overlap
between liquid and ice in mixed phase clouds
© Crown copyright 2005 Page 7
Cloud water PDFs
The histogram of cloud fraction and liquid water contents for low level cloud suggests not enough cloud fractions of 1Tuning the PDF shape and critical relative humidity
values should improve the model
© Crown copyright 2005 Page 8
Other uses of CloudNet data
CloudNet has provided more detailed information which could be used in developing better parametrizations in the future. These include: Ice particle size distributions Inhomogenerity information and cloud overlaps to
inform the radiation scheme assumptionsDiagnostic area cloud fraction representationDrizzle parametrization improvements
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