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Irina Sandu , Jean-Louis Brenguier, Olivier Geoffroy

CNRM/GMEI/ MNPCA. Ambiguous results of Large-Eddy Simulations of marine stratocumulus clouds. Irina Sandu , Jean-Louis Brenguier, Olivier Geoffroy. CNRM/GMEI/ MNPCA. I. Introduction. II. Application of the LES technique for studying the indirect effect of aerosols. Méso-NH as a LES code.

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Irina Sandu , Jean-Louis Brenguier, Olivier Geoffroy

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  1. CNRM/GMEI/ MNPCA Ambiguous results of Large-Eddy Simulations of marine stratocumulus clouds Irina Sandu , Jean-Louis Brenguier, Olivier Geoffroy

  2. CNRM/GMEI/ MNPCA I. Introduction II. Application of the LES technique for studying the indirect effect of aerosols Méso-NH as a LES code Validation on FIRE-I case III. Large-Eddy simulations of different cases of marine stratocumulus IV. Conclusions Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  3. CNRM/GMEI/ MNPCA I. Introduction II. Application of the LES technique for studying the indirect effect of aerosols Méso-NH as a LES code Validation on FIRE-I case III. Large-Eddy simulations of different cases of marine stratocumulus IV. Conclusions Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  4. I. ? ? diurnal variation of the cloud and of the boundary layer aerosols Boundary layer clouds: marine stratocumulus Considerable coverage + optical properties Negative radiative forcing r significant impact on the planetary radiative budget Complexe interaction between dynamics - microphysics - radiation Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  5. I. Twomey (1977): LWP constantNCCN Nc albedo Albrecht (1989): NCCN Nc re Suppression of drizzle formation The cloud life time LWP constant dynamical feedbacks: LWP non constant inseparability of the indirect effects the indirect effects of aerosols 1st indirect effect 2nd indirect effect Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  6. CNRM/GMEI/ MNPCA I. Introduction II. Application of the LES technique for studying the indirect effect of aerosols Méso-NH as a LES code Validation on FIRE-I case III. Large-Eddy simulations of different cases of marine stratocumulus IV. Conclusions Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  7. II. Méso-NH as a LES code Advection scheme – positively defined second order centered scheme Microphysics – Khairoutdinov &Kogan 2000(O. Geoffroy ) –2 moments bulk scheme developed for Sc. • Radiative code (ECMWF) –coding problems: the cloud overlap (O. Thouron) • LW – Savijarvi (1997) • cloud optical • properties SW - Fouquart (1987) not suited for • LES of marine stratocumulus New parametrisation for the single scattering albedo based on aerosol chemical composition for LES modelling of boundary layer clouds Sandu I., P. Tulet and J.L. Brenguier, Geophys. Res. Lett., 32, L19814, 2005 set of parametrisations adequate and coherent Complexe interaction dynamics – microphysics - radiation Turbulence scheme – 3D scheme (Cuxart-2000) – TKE equation +1.5 closure + Deardorff mixing length Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  8. II. Validation of the code LES The initialisation followed the intercomparison exercice (Duynkerke et al. 2004) • 2.5kmX2.5kmX1.2km – 50mX50mX10m • initial profiles • Subsidence w=-1x10-5 x z m/s • Forcings onL et qT (large scale advection) • No precipitations 0.7g/kg 700m L et qT rc(g/kg) 250g/m2 0LT 12LT 0LT 12LT LWP (g/m2) 0LT 12LT 0LT 12LT FIRE I case study (1987) - intercomparison exercice during EUROCS Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  9. CNRM/GMEI/ MNPCA I. Introduction II. Application of the LES technique for studying the indirect effect of aerosols Méso-NH as a LES code Validation on FIRE-I case III. Large-Eddy simulations of different cases of marine stratocumulus IV. Conclusions Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  10. III. CCN impact drizzle, the diurnal cycle amplitude, the LWP, the surface and radiative fluxes, the boundary layer energetics how the system response depends on the external conditions (large scale horizontal advection, subsidence, etc…) Large-Eddy Simulations of different cases of marine stratocumulus Simulations initialized with various CCN concentrations, for several large scale forcings = the impact of CCN on the stratocumulus capped boundary layer evolution Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  11. LWP (g/m2) Nc LWP Nc LWP 0 LT 12 LT 0 LT 12 LT W4 : subsidence w = - 4X10-6 z (m/s) Nccn= 50, 600 cm-3 no large scale advection Nc ~ 40, 220 cm-3 subsidence w = - 6X10-6 z (m/s) Nccn= 50, 600 cm-3 1K/day cooling 1K Nc ~ 40, 220 cm-3 W6 : subsidence w = - 6X10-6 z (m/s) Nccn= 50, 200, 600 cm-3 no large scale advection Nc ~40, 120, 220 cm-3

  12. CNRM/GMEI/ MNPCA I. Introduction II. Application of the LES technique for studying the indirect effect of aerosols Méso-NH as a LES code Validation on FIRE-I case III. Large-Eddy simulations of different cases of marine stratocumulus IV. Conclusions Meeting on the Parametrisation of Boundary Layer Clouds , Toulouse, 3rd – 4th July 2006

  13. short-term response  long-term response IV. Conclusions for specific initial conditions the system response is not unique strong coupling between dynamics - microphysics - radiation the system response to an increase of the cloud droplet concentration reverses from the first diurnal cycle to the next one the trap of 1st order hypotheses !

  14. Questions?

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