1. B3. Microphysical Processes
Deliverables
1. Measurements of water and ice particle size distributions and shapes for the clouds sampled by the FAAM aircraft.
2. Measurements of total ice and water content in the same clouds
3. Distribution of latent heating rates from microphysical processes.
4. Improvement to bulk microphysical schemes in idealised model by using the aircraft measurements as a constraint.

2. Ice crystal concentration per litre and droplet number concentration per cm3 against temperature (bin width 0.5oC)

3. Crystals near cloud top at -35C from 2D-S

4. B655 microphysics plots (afternoon flight, over Chilbolton)

5. Crystal habits from 2D-S in High Z-DR regions near cloud top at about -8C

6. Crystal shapes near cloud top from CPI

7. Reflectivity, differential reflectivity, radial velocity3GHZ scanning

8. Near cloud top away from high Z-DR region dominated by LW at -8C

9. Sharp transition from region of liquid water to region of ice and mixed phase cloud near cloud top

10. Columns, neeedles and droplets lower in cloud at about -4C

11. Cold front

14. Collaborations are ongoing with Chen and his PDRA (Tzuchin Tsai) to test this parameterization in the context of DIAMET case studies (mostly B655 so far)
Some preliminary results are available...

15. Model configuration WRFv3.3.1 with Morrison microphysics
Initialised with ECMWF analysis resolution
3 domains, innermost resolution over southern UK
Simulations performed both with the adaptive habit parameterization and without (i.e. assuming spherical ice)
The adaptive scheme does not yet account for changes in the density of ice during growth (this to come later)

16. B655: Vertical profiles of model fields between 14z-16z, along the Chilbolton radial
Adaptive ice growth
Spherical ice
Columns predicted in H-M zone (aspect ratio ~2)
With the adaptive habit scheme, the predicted ice mass increases by a factor of ~4 in the H-M zone

17. B655: Vertical profile of deposition heating rate between 14z-16z, along Chilbolton radial
Deposition heating rate (K/hr)
Adaptive ice growth
Spherical ice
The deposition heating rate increases by a similar amount; a potentially important diabatic effect

18. B655: Impact of habit parameterization on surface precipitation
Left: Accumulated surface precipitation between 00z-18z for the control and test cases
Right: Timeseries of average surface precipitation rate (mm/hr) within the targeted region.
Shows slight increase at 15z, when the NCFR passes through.
NB – these results don't include the effect of habit on fallspeed yet, and so the effect on precip is likely to be underestimated here...

19. CONCLUSIONS
Cloud tops colder than -30C homogeneous freezing dominate and bullet rosettes dominate with little liquid water.
Clouds with top temperatures warmer than about -30C contain regions of liquid water and regions of primary nucleation near cloud
Crystals grow by vapour diffusion and aggregation as they fall often in concentrated fall streaks related to regions of updraught which supply the water
In a Secondary ice by Hallett-Mossop is very important to the cloud microphysics especially in shallower clouds
H-M Splinters often lead to the highest ice crystal concentrations and highest ice water contents
After correction for fragmentation on probe inlets there is no evidence for any other significant multiplication mechanism. New parameterisation of size distributions may be needed,
Numbers of primary ice are consistent with De-Mott mostly and mostly with a singular nucleation scheme dominated by emersion freezing
Initial results in WRF suggest ice crystal shape effects could be important in diabatic processes and including ice crystal shape in WRF will alter precipitation patterns

20. Future work
Adaptive bulk scheme still needs to be validated against bin microphysics and observations
This work is currently ongoing (using ACPIM)
Results will help to decide whether ice crystal shape effects are important in terms of helping to improve forecast skill
Comparisons between mesoscale models the observations and bin microphysics (ACPIM) needed to establish importance of
Role of ice crystal nucleation processes
Role of secondary Ice
Role of ice crystal density and fall velocity resulting from growth by riming vapour diffusion and aggregation.