Simulation of Cloud Droplets in Parameterized Shallow Cumulus During RICO and ICARTT Knut von Salzen 1, Richard Leaitch 2, Nicole Shantz 3, Jonathan Abbatt 3, Frederic Burnet 4 1 Canadian Centre for Climate Modelling and Analysis (CCCma) ‏, EC, Victoria, Canada 2 Climate Chemistry Measurements and Research, EC, Toronto, Canada 3 Department of Chemistry, University of Toronto, Toronto, Canada 4 CNRM/MGEI, Météo France, Toulouse, France Cloud-Aerosol Feedbacks and Climate (CAFC) research network

ICARTT Experiment Goal: Study air quality, intercontinental transport, and radiation over North America and Europe. Location of Canadian experiment: Near Cleveland, Ohio Time: 2 flights available, August 3 & 16, 2004 Measurements: Canadian Convair 580, R. Leaitch et al. 1Hz Cloud & aerosol microphysics and chemistry

Modelling Approach for Shallow Cumulus - Fundamental Components Parameterizations for mixing of thermodynamic properties. Parameterizations for mixing of cloud droplets. Microphysical model for aerosol and droplet growth (by condensation) for cloud core.

Parameterization for Mixing of Thermodynamic Properties for Shallow Cumulus von Salzen and McFarlane (2002) ‏ von Salzen et al. (2005) ‏ - see also talk by Francesco Isotta - Entraining plume model, based on continuity equations for mass, total water, energy, and momentum. Idealized cumulus lifecycle: Variable cloud top heights and final detrainment. Lateral and cloud-top mixing processes. Non-homogenous clouds: Statistical distributions of thermodynamic properties consistent with mixing line. Cloud-base closure based on simplified mixed layer TKE budget. Recent improvements: Mixing probability and vertical velocity.

Linear mixing for total water (r t ) and moist static energy (h): Evidence for Mixing Line from Observations RICO RF06 ICARTT Ft12 ICARTT Ft21 Cloud environment Cloud core Composites of observations from different levels in the clouds. Dark colours refer to low, light colours to high levels. Crosses: dry samples; bullets: cloudy samples

Total Water Mixing Ratio Probability Distributions ICARTT Ft12ICARTT Ft21RICO RF06 Simulated range Bullets: Mean Simulated Observed (cloud) Observed (clear-sky)

Parameterizations for mixing of thermodynamic properties. Parameterizations for mixing of cloud droplets. Microphysical model for aerosol and droplet growth (by condensation) for cloud core. Modelling Approach for Shallow Cumulus - Fundamental Components

Microphysical Aspects of Turbulent Mixing fraction of environmental air cloud droplet concentration homogeneous ~ conserved thermodynamic tracer inhomogeneous ~ liquid water intermediate cloudy clear

Microphysical Aspects of Turbulent Mixing fraction of environmental air cloud droplet volume homogeneous inhomogeneous intermediate Mixing line Independent columns

Microphysical Aspects of Turbulent Mixing RICO RF06 ICARTT Ft12 ICARTT Ft21 Bullets: FSSP96 Open circles: FSSP124 Composites of observations from different levels in the clouds. Dark colours refer to low, light colours to high levels in clouds. Lines refer to parameterizations.

Parameterizations for mixing of thermodynamic properties. Parameterizations for mixing of cloud droplets. Microphysical model for aerosol and droplet growth (by condensation) for cloud core. Modelling Approach for Shallow Cumulus - Fundamental Components

New Model for Nucleation and Growth of Droplets for Cloud ‏ Core 25 cm/s 50 cm/s 100 cm/s 200 cm/s updraft wind speed Open circles: New model Bullets: Detailed parcel model Fully prognostic numerical solution of droplet growth equation (for condensation). Efficient: Quasi-steady state approximation for supersaturation ► look-up tables. Few iterations for water and energy budgets. Multi-component aerosol size distributions based on PLA method (von Salzen, 2005). Vertical velocity, total water, and moist static energy from shallow cumulus scheme (cloud core conditions). Water-soluble organics in aerosol Water-insoluble organics in aerosol supersaturation (%) height (m)

Parameterizations for mixing of thermodynamic properties. Parameterizations for mixing of cloud droplets. Microphysical model for aerosol and droplet growth (by condensation) for cloud core. Modelling Approach for Shallow Cumulus - Fundamental Components

Droplet Effective Radius – Intermediate Mixing ICARTT Ft12ICARTT Ft21RICO RF06 Simulated range Bullets: Mean Simulated 500 cm cm -3 FFSSP adiabatic FSSP96 FSSP124 obs.

Realistic representation of thermodynamic cloud properties for 3 flights from RICO and ICARTT. Relatively simple convective plume model for cloud droplets, including model for prognostic droplet growth for cloud core and new mixing-line based parameterizations for mixing processes. Broadening of droplet size probability distribution towards smaller sizes owing to increasing probability of diluted air away from cloud base for homogeneous and intermediate mixing. Free parameter in parameterization for intermediate mixing based on fitting without accounting for turbulent mixing time scales yet. No collision/coalescence yet. Future research with focus on effects on climate effects in GCM. Conclusions