Assessment of model performance and potential improvements using

Assessment of model performance and potential improvements using Cloud. Net data Damian Wilson, 12 th October 2005 © Crown copyright 2005 Page 1

Summary § Cloud. Net 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 2

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 Had. GAM © Crown copyright 2005 Page 3

Low level cloud § The low level cloud peak is at too low an altitude § A boundary layer problem? § The model has a large amount of fog and very low cloud in stable boundary layers § Possibly due to inaccuracies in the stable boundary layer turbulent flux profiles JJA: Downwards, stable Observations Had. GAM PC 2 m © Crown copyright 2005 Page 4

Thick liquid water contents § There are not enough of the highest liquid water contents § Possibly 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 © Crown copyright 2005 Page 5

Supercooled liquid water content § The mesoscale model (and to a lesser extent, the global model) has significantly less supercooled liquid water than the observations § Possible adjustment of the overlap between liquid and ice in mixed phase clouds © Crown copyright 2005 Page 6

Cloud water PDFs § The histogram of cloud fraction and liquid water contents for low level cloud suggests not enough cloud fractions of 1 § Tuning the PDF shape and critical relative humidity values should improve the model © Crown copyright 2005 Page 7

Other uses of Cloud. Net data § Cloud. Net 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 assumptions § Diagnostic area cloud fraction representation § Drizzle parametrization improvements © Crown copyright 2005 Page 8