Simulation of the Aerosol Indirect Effect in GCM

Simulation of the Aerosol Indirect Effect in GCM 1 st and Aerosol Indirect Effect Radiative Transfer Microphysics CCN Activation Cloud Dynamics CLOUDNET Onset of Précipitation Evaporation J. L. Brenguier Météo-France 2 nd

ACE-2 Field Campaign June-July 1997 Experimental Strategy To select cloud systems with similar LWP and morphology, but with different aerosol prop. To sample an area of 60 km, about the GCM spatial resolution To synchronize in situ and remote sensing for column closure experiments CLOUDNET Nact=50 cm-3 Nact=250 cm-3 Surface Site Tenerife J. L. Brenguier Météo-France Morocco

ACE-2 Field Campaign June-July 1997 Multi-disciplinary: aerosol chemistry and physics, cloud microphysics cloud radiative transfer First experiment with detailed characterization of aerosols and simultaneous measurements of cloud microphysics in situ and radiative properties from above Observation area of 60 km side sampled during 4 hours: robust statistics BUT Measurements at noon local time No radar/lidar No vertical profile, No diurnal cycle ACE-2 Special Issue of Tellus 2000 JLB et al. JAS 2000 CLOUDNET J. L. Brenguier Météo-France

ACE-2 Field Campaign June-July 1997 JLB et al. 2003 CLOUDNET J. L. Brenguier Météo-France

PACE Cooperative Study between ACE-2 Experimentalists and GCM Modellers for Testing/Developing GCM Parameterizations on the ACE-2 data set Meteo-France: J. L. Brenguier FUBerlin: L. Schüller U Warsaw: H. Pawlowska U Wyoming: J. Snider MPI: J. Feichter Hadley: D. Roberts U Dalhousie: U. Lohmann U Columbia: S. Menon PNNL: S. Ghan U Michigan: J. Penner LMD: J. Quaas PACE Special Issue of JGR August 2003 (Data Analysis Menon et al. JGR 2004 (Model Parameterizations) CLOUDNET J. L. Brenguier Météo-France

PACE METHODOLOGY Series of Closure experiments at a scale relevant to GCM (60 km) on - aerosol activation - radiative transfer - precipitation formation Ø Identify variables relevant to GCM parameterization of AIE and establish relationship with physical variables Ø Build a data base for initialisation and validation of SCM versions of the GCMs (8 ACE-2 case studies) Ø Examine the predictability of the selected variables Ø Test parameterizations and examine feedback processes CLOUDNET J. L. Brenguier Météo-France

1 st Aerosol Indirect Effect CCN Activation Microphysics Well known since 50 years from - in situ measurements - & 1 D to 3 D modelling CLOUDNET J. L. Brenguier Météo-France

Droplet Mean Volume Diameter versus Height above Cloud Base (Pawlowska et al. 2000) N=75 cm-3 208 CLOUDNET 51 256 134 114 178 134 J. L. Brenguier Météo-France

Can we predict CDNC at the GCM resolution scale from predicted aerosol properties and a diagnostic of updraft intensity qc(h)>0. 9 qcad(h) Ndrizzle< 2 cm-3 0. 4 H < h < 0. 6 H Pawlowska et al. 2000 CLOUDNET J. L. Brenguier Météo-France

CCN Activation Microphysics Closure Experiments State of the Art CDNC predicted with detailed process models initialised with measured aerosol physico-chemical properties and w OVERESTIMATES measured CDNC Snider et al. 2003 CLOUDNET J. L. Brenguier Météo-France

State of the art in GCM simulation of AIE Menon et al. 2004 CLOUDNET J. L. Brenguier Météo-France

CCN Activation Microphysics CONCLUSIONS : NOT SO BAD Discrepancies attributed to - incomplete characterization of aerosol properties - and biased vertical velocity GCM Parameterization of activation is NOT AN ISSUE except subgrid scheme to derive local w from grid TKE and better representation of aerosol physico-chemical properties CLOUDNET J. L. Brenguier Météo-France

1 st Aerosol Indirect Effect Microphysics Radiative Transfer Numerous experimental evidences from multispectral radiances - satellites - close remote sensing BUT - Very few that discriminate between impact of microphysics and impact of LWP CLOUDNET J. L. Brenguier Météo-France

1 st Aerosol Indirect Effect Microphysics Radiative Transfer Measured reflectances in VIS and NIR, with H-N grid N remotely retrieved values versus Nact CLOUDNET J. L. Brenguier Météo-France

CLOUDNET J. L. Brenguier Météo-France

CLOUDNET J. L. Brenguier Météo-France

Radiative Transfer Microphysics Closure Experiments State of the Art CDNC predicted with detailed radiative (inverse) transfer models initialised with measured multispectral radiances AGREE with measured CDNC CLOUDNET Schüller et al. 2003 J. L. Brenguier Météo-France

Satellite Monitoring of the AIE Correlation between Cloud Optical Thickness and Droplet Effective Radius -1 CLOUDNET J. L. Brenguier Météo-France

Microphysics Radiative Transfer CONCLUSIONS : QUITE GOOD Discrepancies attributed to - heterogeneities of the microphysical fields - optical properties of aerosols and droplets GCM Parameterization of radiative transfer is AN ISSUE because of the poor representation of clouds in GCM, not because of the susceptibility to CDNC CLOUDNET J. L. Brenguier Météo-France

Measurements of the Aerosol Indirect Effect 2 nd Aerosol Indirect Effect Microphysics Onset of Précipitation Evaporation Well known since 50 years from - in situ measurements - & 1 D to 3 D modelling has been carefully explored for weather modification, without success though!!! CLOUDNET J. L. Brenguier Météo-France

Microphysics Onset of Précipitation Closure Experiments State of the Art Measured drizzle concentration depends on the maximum radius droplets can reach in a cloud layer and the threshold (10µm) corresponds to the value derived from detailed modelling of droplet coalescence Pawlowska et al. 2003 CLOUDNET J. L. Brenguier Météo-France

Microphysics Précipitation Evaporation CONCLUSIONS : Very bad Pawlowska et al. 2003 Menon et al. 2003 Aerosol-CNES September 2003 J. L. Brenguier Météo-France

Parameterization of precipitation in GCM Detailed microphysics 1 to 3 -D (50 to 200 variables) 3 -D CRM Runs (diverse conditions) Tripoli-Cotton, Beheng, Khairoutdinov-Kogan Bulk microphysics for CRM (3 variables: N, qc, qr) Auto-conversion (N, qc) and Accretion (N, qc, qr) Tuning bulk coefficients to account 3 -D bulk CRM Runs (meso-scale) for GCM grid smoothing effects Bulk microphysics for GCM (2 variables : N, q Bulk microphysics for GCM (2 variables : N, H) c) Average precipitation rate from multi-cells in stationary state Auto-conversion (N, qc) (Accretion diagnosed) EGS 7 April 2003 Nice J. L. Brenguier Météo-France

CRM versus GCM PARAMETERIZATION OF PRECIPITATION H. Pawlowska CLOUDNET J. L. Brenguier Météo-France

Précipitation Evaporation Microphysics Model variability attributed to the use of CRM bulk parameterizations of auto-conversion and accretion in GCM. New bulk parameterizations are tested (ACE 2, DYCOMS), where precipitation rate only depends on LWP and CDNC Pawlowska et al. 2003 CLOUDNET J. L. Brenguier Météo-France

Microphysics Cloud Life Cycle Experimental strategy for BL clouds Aerosols have a strong impact on the onset of precipitation and precipitation rate, but it is not obvious that they have an impact on the cloud life cycle. In BL clouds, the contribution of precipitation to the water budget is comparable to the contributions of radiative & turbulent fluxes. The uncertainty in measurements of these fluxes are still higher than the fluxes themselve. Requires long term monitoring of the cloud life cycle at a super site equipped with surface fluxes, radar and lidar remote sensing and concomitant aerosol characterization CLOUDNET J. L. Brenguier Météo-France

State of the art in GCM simulation of AIE CONCLUSION Most of the uncertainty comes from the coarse representation of thin BL clouds in GCMs MVDR at cloud top H 1/3, Optical depth H 5/3, Precipitation rate H 4 Priorities - Finer vertical resolution and sub-grid vertical schemes - « GCM Bulk » parameterization of rain formation - Reduce the bias in the prediction of Nact - Better understand the heterogenous bias in relation with the second AIE - Parameterizations of the aerosol processing in clouds EGS 7 April 2003 Nice J. L. Brenguier Météo-France

Boundary Layer Clouds A=0. 50 Entrainment-Mixing rl=0. 2 g kg-1 Radiative Transfer Microphysics CCN Activation rv=20 g kg-1 Turbulent Fluxes rv 1 st and 2 nd Aerosol Indirect Effect T Onset of Précipitation Evaporation A=0. 05 CLOUDNET J. L. Brenguier Météo-France