Transcript ppt - Cosmo
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 1 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 2 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 3 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 4 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) 5 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 6 Ice nucleation: current status: Homogeneous Freezing Heterogeneous Freezing ni T ni,0 e0.2Tm 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- 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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 17 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 18 Revision of cloud-radiation feedback Total QI Total QS – factor 5 and more ! Ulrich Blahak, DWD, COSMO General Meeting 2013 Sibiu 19 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 20