1. The representation of ice hydrometeors in ECHAM-HAM
Specific humidity
Specific humidity
Cloud cover
Precipitation

2. The phase of precipitating clouds
5 years of data from CloudSat-CALIPSO ( )
→ Precipitation in mid-latitudes and above continents is dominated by clouds having ice tops
Ice phase
Super cooled liquid fraction (SLF) has a strong impact on Equilibrium climate sensitivity
Tan et al., Science, 2016
Liquid phase
Mixed phase
Phase fraction
Remo Dietlicher - C2SM user workshop

3. Remo Dietlicher - C2SM user workshop
Cloud ice in models
CMIP5 GCMs and reanalysis for globally averaged (80°N – 80°S), annual mean vertical profiles of ice water content.
All models are in radiative balance
Very wide spread in IWC
→ Radiative balance is achieved by a wide range of ice properties
→ Models disagree on the representation of cloud ice
Remo Dietlicher - C2SM user workshop

4. How to describe cloud ice
Two category scheme
Single category scheme
Ice
Surface
Precipitation
Radiation
Radiation
α= 𝑣Δ𝑡 Δ𝑧
Ice
Growth
Snow
Precipitation
Surface
Remo Dietlicher - C2SM user workshop

5. Cloud phase and the description of ice
Idealized simulation
Single column with external forcing from 800 – 600 hPa:
12 hours moistening
12 hours stable
12 hours drying
Microphysics only (no radiation, convection, diffusion, transport)
→ Cloud phase is heavily influenced by description of ice hydrometeors!
Remo Dietlicher - C2SM user workshop

6. Remo Dietlicher - C2SM user workshop
Conclusions
There is a large gap between resolved scales and microphysics
Cloud phase is important for precipitation formation and equilibrium climate sensitivity
Description of cloud ice strongly affects cloud phase
A single category removes the need for the heuristic partitioning of cloud ice
Thank you!
Remo Dietlicher - C2SM user workshop