WG3a activities in cloud
microphysics and
radiation
Ulrich Blahak, for the large part on behalf of Axel Seifert
German Weather Service, Offenbach
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Outline
 Microphysics:
 Activities in the last year
 Short term plans
 Long term plans
 The same for radiation
 … and revised cloud radiation coupling
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Microphysics: recent work
 Improvement of supercooled LWC in mixed phase clouds (F. Rieper, motivated
by air craft icing forecasts at DWD)
 Development of improved treatment of cirrus ice clouds for current onemoment schemes (PhD of C. Köhler, DWD)
 Development of improved snow melting parameterization (PhD of C. Frick,
DWD)
 Interface to 2-moment scheme in official Version; code itself and necessary
lookup table files available on DWD ftp server. Still missing „User Guide“ …
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Improvement of Supercooled LWC
 Much too less supercooled LWC in mixed phase clouds
 Changes to the microphysics:
 Reduced diagnostic number of ice particles as function of T (before, it was
unplausibly too high), therefore reduction of Bergeron-Findeisen-process in
mixed phase clouds
 Reduction of rain freezing rates (before, it was unplausibly too high)
 Parameterization of subgrid scale effects on liquid water layers on top of ice
cloud layers.
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Result: reduced underprediction
Aerosol
Ice & SLW
Ice
Observation
January 18, 2013 Lindenberg
COSMO (new: Ni)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by F. Rieper, DWD
COSMO
COSMO (old)
COSMO (new: Ni+SLW)
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Result: impact on supercooled LWP
January 18, 2013 Lindenberg
Observation
good retrieval
COSMO-EU
COSMO-EU (old)
(new: Ni+SLW)
COSMO-EU (new: Ni)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by F. Rieper, DWD
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Ice nucleation: current status:
Homogeneous Freezing
Heterogeneous Freezing
ni T   ni,0 e0.2Tm elt T 
Cloud
droplet
Liquid
Aerosol
( H 2SO 4 )
Missing
Immersion-
Contact-
Condensation-
Thomas Leisner, Institut für Meteorologie und Klimaforschung FZ Karlsruhe und
Institut für Umweltphysik, Uni Heidelberg (modified)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by C. Köhler, DWD
Deposition-
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Changes in the Cloud Ice Microphysics
• Implementation of state-of-the-art parameterisations for homogeneous
and heterogeneous nucleation
• New prognostic model variables n i
 2-moment cloud ice scheme (still monodisperse size distribution)
• Changes in treatment of depositional growth for cloud ice and snow
• Limitation of heterogeneous nucleation with prognostic budget variable
for activated ice nuclei ni ,nuc
ni ,nuc
t
   (v ni ,nuc ) 
ni ,nuc
t

het
ni ,nuc
 mix
• Introduction of cloud ice sedimentation
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides
C. Köhler, DWD
DLR –by
06/06/2011
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COSMO-DE Model
MSG/SEVIRI
COSMO Modell
COSMO-Ice
 Implemented in COSMO
Version 4.18
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by C. Köhler, DWD
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GME Model
• Overestimation of ice water
content (IWC) of the GME is
reduced
• RMSE reduced with the new
cloud ice nucleation scheme
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by C. Köhler, DWD
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GME Model
• Ice supersaturation improved due to new depositional growth
• In-cloud ice supersaturation is allowed for. IFS assumes in-cloud saturation,
which is not compliant with in situ measurements
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
Slides by C. Köhler, DWD
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New snow melting scheme
 New prognostic snowflake water content
 Enables better parameterization of the melting process
 Leads to slower melting, more in accordance with observations
Old
New
(Frick et al. 2013, GMDD, under review)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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New snow melting scheme
Meltwater on snow flakes,
same section as slide before
Different day, different
region
One can have partially melted snow on the ground.
Affects prediction of precipitation phase on the ground in
winter time!
(Frick et al. 2013, GMDD, under review)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Microphysics: plans
 Short term (2013 – 2017):
 Common COSMO / ICON physics library
 Investigate dry precipitation bias in summer time
 Further testing of the works of C. Köhler and C. Frick
 Continuing work of F. Rieper regarding supercooled LWC, demand of aviation
forecasters (aircraft icing)
 2-moment scheme: further studies to evaluate benefit in operational NWP; consistent
data assimilation, otherwise we will most likely not see the full benefit
 Towards explicit hail forecasting with 2-moment scheme:
 improvement of hail melting / shedding following methodology of C. Frick
(Postdoc work of V. Sant in HD(CP)2 , Hamburg)
 Resolution requirements?
 Longer term (2018 – 2020):
 Keep an eye on scientific developments regarding subgrid scale processes in cloud
microphysics parameterization (effects of turbulence and spatial inhomogeneity)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Microphysics: recent publications
 Frick, C., A. Seifert, and H. Wernli, A bulk parameterization of melting
snowflakes with explicit liquid water fraction for the COSMO model version
4.14, Geosci. Model Dev. Discuss., 6, 2927-2966, 2013
 Köhler, C: Cloud ice particle nucleation and atmospheric ice supersaturation in
numerical weather prediction models, PhD thesis, 2013
 Seifert, A., Köhler, C., and Beheng, K. D.: Aerosol-cloud-precipitation effects
over Germany as simulated by a convective-scale numerical weather
prediction model, Atmos. Chem. Phys., 12, 709-725, doi:10.5194/acp-12-7092012, 2012
 Naumann, A. K., Seifert, A., and Mellado, J. P.: A refined statistical cloud
closure using double-Gaussian probability density functions, Geosci. Model
Dev. Discuss., 6, 1085-1125, doi:10.5194/gmdd-6-1085-2013, 2013
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Radiation: recent work
 New modis derived „total“ albedo (Frank Brenner, DWD)
 External parameters for orographic radiation corrections finally available in new
EXTPAR
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Radiation: plans
 Short Term (2013 – 2017):
 Common COSMO / ICON physics library
 Test parameterization of 3D radiation effects (work from Uni Munich within
Extramural Research program), TICA, McICA
 Test McSI – Monte Carlo Spectral Integration methods (B. Ritter)
 Revision of cloud - radiation feedback (U. Blahak)
 Test alternative scheme RRTM for COSMO (available via common physics
library):
Consistent coupling with ICON
RG92 has problems for domain heights >~ 25 km
 Longer Term (2015 – 2017):
 Likely: Revision of cloud - radiation feedback cont.
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Revision of cloud radiation feedback
 In the COSMO radiation scheme (Ritter & Geleyn 1992), the optical properties
(extinction coeff., single scattering albedo, asymmetry factor) only depend on
QC respectively QI.

Nowadays more modern parameterizations based on an effective radius Re
are available.

From inherent assumptions about N(D) and particle shapes in state-of-theart microphysical models Re can be deduced.

Then: optical properties = fct (QX, Re, λ)
 For the gridscale clouds, only a fraction k=0.5 of QI and/or QC is considered in
the radiation scheme („tentative“ effective factor to take into account subgrid
scale variability). Test larger, more realistic value for todays models.
 Radiation scheme is only aware of cloud droplets and cloud ice! Extend to
precipitating species (most importantly snow)
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Revision of cloud-radiation feedback
Total QI
Total QS – factor 5 and more !
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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Revision of cloud-radiation feedback
Case study COSMO-DE, 13.6.2012, 00UTC run,
domain average T_2M
Control
+ Tegen aerosols
+ hydrometeor
radiative properties
depending on Reff
+ qg, qs
+ radqfact 0.5 -> 0.75
Potential big impact, but it looks not always so nice!
Careful re-tuning of the model necessary. Current
model tuned to compensate the cloud radiative bias!
- - - - Synop Obs.
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu
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