1. A model of sea salt aerosol for Cape Grim Preliminary investigations
Martin Cope, Sunhee Lee, Melita Keywood and John Gras

2. PROJECT DESCRIPTION
This is a project with a long-term goal of contributing to the understanding of the Southern Ocean coupled aerosol-chemistry system
Stage 1 Sea salt aerosol
Largest natural aerosol production rate (1000 – Tg per year)1
Contributes 30-75% of all natural aerosol sources1
Dominant contributor to visibility reduction in the clean MBL + direct radiative forcing
Can compete with sulfate aerosol as cloud condensation nuclei (5% to 90% of marine CCN)1
Estimates of radiative forcing are -0.6 to -2 W m-2 (light winds) and -1.5 to -4 W m-2 (or greater) in high winds1
Is an important source of halogens to the atmosphere
Task. Using modelling and measurement, investigate the processes leading to the observed sea salt distributions at Cape Grim
(Zakey et al. 2008)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

3. MODELLING SYSTEM (TAPM-CTM)
The Air Pollution Model (TAPM)
NUMERICAL WEATHER PREDICTION
3-d, Eulerian, nestable;
incompressible, non-hydrostatic;
winds, temperature, pressure, water vapour, cloud and rain water, turbulence kinetic energy and eddy dissipation rate;
surface scheme (soil and vegetation);
cloud microphysics scheme;
radiation scheme;
Chemical transport model (CTM)
Gas phase chemical transformation
Cloud chemistry
Aerosol inorganic chemistry
Aerosol organic chemistry
Wet and dry deposition
Natural sources (sea salt emissions, dust, biogenic)
Simple sectional aerosol scheme
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

4. SEA SALT EMISSIONS MODEL
OPEN OCEAN
F0 = rate of droplet generation per unit area per increment of particle radius (m-2 s-1 mm-1)
(Originally from Monahan et al.1986
Modified by Gong 2003)
SURF ZONE
(from Gong and Barrie 1997)
(D=2r)
(De Leeuw et al. 2000)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

5. MODEL CONFIGURATION 27-km 1-km 3-km 9-km Numerical weather prediction
4 nested grids in the horizontal
22 levels in the vertical (up to 8000 m)
GASP analysis for met boundary conditions
13 month simulation (Jan 2006 – Jan 2007)
Chemical transport modelling
Sea salt aerosol treated as tracer
9 size fractions (0.03 – 20 mm)
Open ocean + surf zone emissions
Transport + diffusion
Dry deposition
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

6. MODEL OUTPUT February 2006- 27-km grid
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

7. MODEL PERFORMANCE Comparison of observed and modelled sodium mass
CTM-w shore break
CTM-w/o shore break
Obs
Comparison of observed and modelled sodium mass
Jan 2006 – Jan 2007
7-day sampling interval using hi-vol sampler
Collecting particles of < 10 mm (at ambient RH)
Screened for soil contamination
Gong et al. 1997
Observed and modelled monthly mean Na+
Detailed sea salt aerosol model
1-D climate column model
Dec 1988 – May 1993
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

8. Na+ concentration wind rose
MODEL PERFORMANCE
Na+ concentration wind rose
Keywood 2003 (Baseline )
1983 – 1996 data
Data collected by Miami University
All wind directions
Current study
13 month simulation
1-km model grid
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

9. PERFORMANCE SEA SALT AEROSOL MASS SIZE DISTRIBUTION MOUDI data
MODEL (Feb and Aug 2006)
9 size fractions (mm)
; ;
; ;
; ;
; ;
MOUDI data
10 samples
Summer 2002/2003
Base line conditions
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

10. PERFORMANCE- SUMMARY Better performance using the
(+ surf)
Better performance using the
open ocean model only;
Surf zone model sensitive to surf zone
length scale (satellite data?)
Issues with over prediction
at the lowest concentrations
Size distribution looks promising however need to look at sensitivity of model results to the number + size of sections
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

11. MODEL RESOLUTION TESTS
1-km
27-km
Higher sea salt concentrations predicted on the 27-km grid (better blocking on the 1-km grid?)
Results are less well correlated but have better slope
27-km
27-km
1-km
1-km
OBS
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

12. WHERE NEXT?
Add more sections to the aerosol module (between 5 and 20 mm)
Wet deposition + test all formation and loss processes
Review assumptions of surf zone emission model
Review spatial scales + limited area model assumptions
Chemistry
Inorganic
Organic
Test UKCA chemistry and aerosol schemes
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

13. INFORMING ACCESS
Chemistry-aerosol UKCA
Australian Community Climate and Earth-System Simulator
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

14. UKCA
Global Model inline in UK UM atmospheric model framework for advection, diffusion, convection, deposition, etc
Tropospheric Chemistry (gas-phase, with 24 Species (+14 in Extended Mode, +9 in Aerosol Mode) including NOx and speciated VOCs, Ozone, Methane, Sulfur Cycle, NH3)
Stratospheric Chemistry (gas-phase and heterogeneous, with 15 Species (+7 in Extended Mode) including NOx and N2O, Ozone, Methane, Sulfur Cycle, CLOx, BrOx, CFC’s)
Aerosol scheme (EC, OC, dust, SOA, nitrates, sulphates, sea salt aerosol, linked into chemistry schemes)
Fast interactive Tropospheric and Stratospheric Radiation scheme (FAST-J) for species reaction rates with gas/aerosol feedback
Chemical Compiler to enable code generation for new species/schemes
Emissions provided with the model, including some interactive components (e.g. biogenic and wetland schemes; salt emissions?)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

15. Thank you Thank you Martin Cope Principal Research Scientist
The Centre for Australian Weather and Climate Research
A partnership between CSIRO and the Bureau of Meteorology
Martin Cope
Principal Research Scientist
Phone:
Web:
Thank you
Thank you