Bin resolved modeling of ice microphysics

Wolfram Wobrock, Andrea Flossmann

Workshop on Measurement Problems in Ice CloudsZurich, Switzerland

July 5-6, 2013

Ice microphysics in clouds

Cotton et al, 2011

MODEL Configuration in 3Da 3D cloud model with detailed microphysics

Example: a cumulonimbus cloud

Necessity to follow at every grid point env. 40 classes per cat.

=> Limits regarding computer time and storage, in particular for meso-scale models

Bulk schemes

• 1 Moment schemes:Walko et al (1995): pristine ice, snow, aggregates, graupel and hail, 3D Straka, Mansell (2005): 10 ice categories : two ice crystal habits (column and plate), rimed cloud ice, snow (ice crystal aggregates), three categories of graupel with different densities and intercepts, frozen drops, small hail, and large hail, 3D

• 2 Moment schemes:Meyers et al (1997): mixing ratio and number concentration of rain, pristine ice crystals, snow, aggregates, graupel and hail, 3DSeifert et al (2006): cloud ice, snowkflakes, graupel, prescribed G distributions, 2DMorrison, Grabowski (2007): mixing ratio due to vapour deposition , mixing ratio due to riming, ice number concentration, 2D kinematic

MIN-BIN-Configuration:

• Drop number density distribution: dN/d(log D), assuming spherical form (D: equiv. diameter)

• Ice particle number density distribution:

200µm

500µm

500µm500

µm

500µm

Needs at least 2 informations, instead of just diameter!Which parameters to select?• 2 dimensions (largest, smallest?)• Mass + density?• Volume + surface?

Currently: just one parameter used (e.g. dimension or mass); other parameters are prescribed

Bin ice microphysics models:

• Radius coordiante:Hall (1980): 18 categories ice crystals, 10 for transistion, 23 for graupel, 2DFarley and Orville (1986): hailRespondek et al (1995): ice crystals, graupel, 2DKhvorostyanov, Sassen (1998): ice crystals, mass equ. radius, 2D/3D

• Mass coordinates:Reisin et al (1996): ice crystals, graupel, snow, 2DOvtchinnokov, Kogan (2000): smallest 15 categories are ice crystals while the largest 13 categories are graupel, 3DFlossmann, Wobrock (2010): spherical ice particles, 3DKhain et al (2011): ice crystals (plate-, columnar- and branch types), aggregates, graupel and hail, 2D

Processes:

• Nucleation:

The onset temperatures and relative humiditiesfor deposition/condensation freezing and immersion freezing for bioaerosols,solid ammonium sulphateand BC (soot) Adapted from Hoose andMohler (2012).

Which particles form ice (chemical composition, size) under which atmospherical conditions (temperature, humidity)?

Processes:

• Vapour deposition:

Mass growth as a funtion of the capacitance C of a corresponding conductor (information on form: spherical, disk, spheroid,..)

Processes:

• Sedimentation:

Terminal velocity as a funtion of theselected parameters ?

Processes:

• Riming and aggregation:

Collection efficiencies as a funtion of theselected parameters ?

Processes:

• Melting:

Processes:

• Radiation:

0.65 0.70 0.75 0.80 0.85 0.90asym m etry param eter

0

200

400

600

800

1000

1200

1400

1600

1800

heig

ht (

m)

cristaux

gouttes

Optical parameters as a funtion of theselected size and form parameters ?

Conclusion:

• Modelling of the ice phase in clouds is trapped between:

Not enough information andToo much information

• What are the most adapted parameters and how do all processes relate to these (2?) parameters?