CloudNET meeting: Malcolm Brooks, April 2005 Observatoire de Paris

1. CloudNET meeting: Malcolm Brooks, April 2005 Observatoire de Paris

2. Contents The presentation covers the following sections • Cloud fraction means • IWC means • Filtering model IWC to mimic obs problems • Adiabatic LWC means • Filtering model LWC? • Categorizing profiles by Met. Regimes

3. Cloud fraction means

4. IWC means

5. Filtering Model IWC The observations are filtered by removing profiles with rain or unknown liquid water attenuation. At each model level, we need to characterise the effect this has on the observed IWC distribution – so we can apply the same effect to filter the observations.

6. Filtering Model IWC Step 1: Observed and model distirutions of IWC are normalised, so as to be comparable.

7. Filtering Model IWC Step 2: The ratio of the unfiltered IWC to the filtered IWC is calculated in the observations. The varies with the Normalised IWC

8. Filtering Model IWC Step 3: Use a fit of this ratio to filter the model IWC, as the normalised IWC varies.

9. Filtering Model IWC Step 5: Convert the Normalised model IWC back to real units….

10. IWC means – After filtering model IWC

11. IWC means – Compare with ’99-’00 at Chilbolton

12. LWC means The Observed LWC appears higher than all the observations shown. When radiometers not usable, assumed to be adiabatic: some filtering required equivalent to the work done on the IWC? - - - Dashed black line shows adiabatic LWC

13. Regimes • What criteria to use to define the “background meteorology”? • - Vertical velocity (smoothed) • - Boundary layer stability. • Which models will these be obtained from? • - “ensemble approach” • How will the thresholds be defined?

14. Regimes Correlations between cloud fraction and vertical velocity: Chilbolton, ’99-’00

15. Regimes

16. Regimes – vertical velocity Not all models are included to define regimes: RACMO – uses ECMWF analyses Met Office Global model – too similar to the Mesoscale model

17. Regimes – vertical velocity Regime criteria are normalised to account for the different distributions from the different models.

18. Regimes – vertical velocity ←Neutral tercile Descending tercile → ←Ascending tercile

19. Regimes – effect of vertical velocity at 500hPa Descending tercile Neutral tercile Ascending tercile

20. Regimes - boundary layer stability

21. Regimes – boundary layer stability

22. Regimes – effects of boundary layer stability << Most Stable Stable/Neutral Convective/Neutral Convective >>

23. Regimes – Combined regimes Combined with 3 Boundary layer types, gives 12 combinations!

24. Regimes – Combined regimes 300hPa / 750hPa: ↓ / ↓ ↓ / ↑ ↑ / ↓ ↑ / ↑ Convective BL: Neutral BL: Stable BL:

25. Regimes – Combined regimes – DJF only 300hPa / 750hPa: ↓ / ↓ ↓ / ↑ ↑ / ↓ ↑ / ↑ Convective BL: Neutral BL: Stable BL:

26. Conclusions • Model IWC can be filtered to mimic instrumental effects: • models do not agree with CloudNET IWC means – algorithm changed since ’99-’00 period. • Comparisons with more radar/lidar algorithms would be useful. • Comparison of adiabatic LWC with models shows large disagreements • more work needed on what the observations mean. • Regimes defined using vertical velocity and boundary layer stability are useful. • Combining the ascent/ descent at 300 and 750 hPa and the boundary layer stability gives a ‘final’ regime definition.