Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 1
WG3a activities in cloud microphysics and
radiationUlrich Blahak, for the large part on behalf of Axel Seifert
German Weather Service, Offenbach
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 2
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 3
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 one-moment 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 4
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 5
COSM
OCO
SMO
Aerosol
Ice & SLWIce
Obs
erva
tion
Obs
erva
tion
January 18, 2013 LindenbergJanuary 18, 2013 Lindenberg
COSMO (old)
COSMO (new: Ni)
COSMO (new: Ni+SLW)
Result: reduced underprediction
Slides by F. Rieper, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 6
COSMO-EU (old)
January 18, 2013 LindenbergJanuary 18, 2013 Lindenberg
Observation good retrieval
COSMO-EU (new: Ni)
COSMO-EU (new: Ni+SLW)
Result: impact on supercooled LWP
Slides by F. Rieper, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 7
Missing
Clouddroplet Immersion- Deposition- Condensation-
Thomas Leisner, Institut für Meteorologie und Klimaforschung FZ Karlsruhe und Institut für Umweltphysik, Uni Heidelberg (modified)
Homogeneous Freezing Heterogeneous Freezing
Contact-LiquidAerosol( )
42SOH
2.00,
TTii
meltenTn
Ice nucleation: current status:
Slides by C. Köhler, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 8DLR – 06/06/2011
• Implementation of state-of-the-art parameterisations for homogeneous and heterogeneous nucleation
• New prognostic model variables
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
• Introduction of cloud ice sedimentation
Changes in the Cloud Ice Microphysics
mix
nuci
het
nucinuci
nuci n
t
nnv
t
n
,,
,, )(
in
nucin ,
Slides by C. Köhler, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 9
COSMO-DE Model
COSMO-Ice
MSG/SEVIRI
Implemented in COSMO Version 4.18
COSMO Modell
Slides by C. Köhler, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 10
GME Model
• Overestimation of ice water content (IWC) of the GME is reduced
• RMSE reduced with the new cloud ice nucleation scheme
Slides by C. Köhler, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 11
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
Slides by C. Köhler, DWD
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 12
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
(Frick et al. 2013, GMDD, under review)
Old New
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 13
New snow melting scheme
(Frick et al. 2013, GMDD, under review)
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!
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 14
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 15
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-12-709-2012, 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 16
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 17
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 18
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-the-art microphysical models R
e 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 19
Revision of cloud-radiation feedback
Total QI Total QS – factor 5 and more !
Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 20
Revision of cloud-radiation feedback
Case study COSMO-DE, 13.6.2012, 00UTC run, domain average T_2M
- - - - Synop Obs.
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!
