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

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 – 10000 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

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

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

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

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

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

Na+ concentration wind rose MODEL PERFORMANCE Na+ concentration wind rose Keywood 2003 (Baseline 1999-2000) 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

PERFORMANCE SEA SALT AEROSOL MASS SIZE DISTRIBUTION MOUDI data MODEL (Feb and Aug 2006) 9 size fractions (mm) 0.039-0.078; 0.078-0.156; 0.156-0.313; 0.313-0.625; 0.625-1.250; 1.250-2.500; 2.5-5.0; 5.0-10.0; 10-20.0 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

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

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

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

INFORMING ACCESS Chemistry-aerosol UKCA Australian Community Climate and Earth-System Simulator http://www.cawcr.gov.au/file/access2007.pdf The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

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

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: 03 9239 4596 Email: martin.cope@csiro.au Web: www.cawcr.gov.au Thank you Thank you www.cawcr.gov.au