Simulation of Cloud Droplets in ParameterizedShallow Cumulus During RICO and ICARTT

Knut von Salzen1, Richard Leaitch2, Nicole Shantz3, Jonathan Abbatt3, Frederic Burnet4

1Canadian Centre for Climate Modelling and Analysis (CCCma), EC, Victoria, Canada2Climate Chemistry Measurements and Research, EC, Toronto, Canada3Department of Chemistry, University of Toronto, Toronto, Canada4CNRM/MGEI, Météo France, Toulouse, France

Cloud-Aerosol Feedbacks and Climate (CAFC) research network

ICARTT Experiment

Goal: Study air quality, intercontinental transport, and radiationover North America and Europe.

Location of Canadian experiment: Near Cleveland, OhioTime: 2 flights available, August 3 & 16, 2004Measurements: 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 ThermodynamicProperties 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.

10f

Linear mixing for total water (rt) and

moist static energy (h):

Evidence for Mixing Line from ObservationsRICO 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 Ft12 ICARTT Ft21RICO RF06

Simulated range

Bullets: Mean

SimulatedObserved (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

clou

d d

rople

t co

nce

ntr

ati

on

homogeneous

~ conserved thermodynamic tracer

inhomogeneous

~ liquid water

intermediate

cloudy clear

Microphysical Aspects of Turbulent Mixing

fraction of environmental air

clou

d d

rople

t volu

me

homogeneous

inhomogeneousintermediate

Mixing line Independent columns

Microphysical Aspects of Turbulent Mixing

RICO RF06 ICARTT Ft12

ICARTT Ft21

Bullets: FSSP96Open circles: FSSP124

Composites of observations fromdifferent 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 Dropletsfor Cloud Core

25 cm/s50 cm/s100 cm/s 200 cm/s

updraft wind speedOpen circles: New modelBullets: 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 (%) supersaturation (%)

he

igh

t (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 Ft12 ICARTT Ft21RICO RF06

Simulated range

Bullets: Mean

Simulated500 cm-3

1000 cm-3

FFSSP

adiabatic

FSSP96FSSP124

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