1. © Crown copyright Met Office Overview of Cloud Scheme Developments at the Met Office Cyril Morcrette 17-18 November 2009, Reading University

2. © Crown copyright Met Office Cyril Morcrette A diagnostic scheme T q T p q v q c C Then forget everything and start again next timestep A prognostic scheme SW LW BL PPN CV LSA Init Erosion T q v q c p C  Advect, and remember values for start of next timestep. Diagnostic vs. Prognostic Cloud Schemes

3. © Crown copyright Met Office Annual-Mean Liquid and Ice Water Paths Cyril Morcrette But how have these equilibrium states been reached? Marine Stratocumulus (off coast of South America, VOCALS area)

4. © Crown copyright Met Office Short-wave Long-wave Boundary-layer Erosion Large-scale precipitation Convection Advection Initialization Pressure change Total Cyril Morcrette South American Stratocumulus (“VOCALS” area Sept-Oct-Nov) Convection, longwave cooling and boundary- layer mixing are the 3 main sources of cloud in Sc region.

5. © Crown copyright Met Office Testing PC2 performance in NWP Cyril Morcrette Control PC2 PC2 gives more ice cloud fraction, similar IWC and reduced liquid cloud fraction and LWC. But this is a model vs model comparison. What do the observations show?

6. © Crown copyright Met Office Cyril Morcrette Operational Model Vanilla PC2 Bulk Cloud Fraction log10 (LWC) kg m-3 log10 (IWC) Time 4-10 Dec 2008 Height 0-12 km 0.0 0.5 1.0 -7 -6 -5 -4 -3 -2 Extract Control and PC2 model data over Chilbolton Need to compare quantitatively against obs. Opportunity to validate a future model and then “tune” the model and then validate again, showing improvement and hence produce a better model as a result of early collaboration with Reading.

7. © Crown copyright Met Office Aircraft Icing Depends on: Super-cooled Liquid Water Content Air temperature Aircraft temperature Cloud fraction Freezing drizzle Icing intensity and likelihood are two different things: e.g. low probability of heavy icing c.f. high probability of light icing Need a sensible index.

8. © Crown copyright Met Office Current Icing Algorithm The icing index, I, takes a value between 0 and 1. If air temperature is between 0 dec C and -20, and if cloud fraction >0, then I =RH Otherwise I =0 That’s it.

9. © Crown copyright Met Office q cl Proposed New Icing Algorithm If temperature is between 0 and -20 deg C (or lower) Use cloud fraction and condensate information from PC2 to calculate PDF of total water (ie q T =q v +q cl ) Use methodology described in Wilson and Gregory (2003). qT’qT’ qsat(T,p) Super-cooled LWC threshold obtained from aviation industry Icing Index is fraction of the cloud fraction where sufficiently high water contents are expected. Skill in fc SCLWC could be found from radar/lidar obs. I would like to collaborate on this please.

10. © Crown copyright Met Office Questions