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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

CNRM/GMEI/ MNPCA

Ambiguous results of Large-Eddy Simulations

of marine stratocumulus clouds

Irina Sandu , Jean-Louis Brenguier, Olivier Geoffroy

slide2

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

slide3

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

slide4

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

slide5

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

slide6

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

slide7

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

slide8

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

slide9

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

slide10

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

slide11

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

slide12

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

slide13

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 !