Effects of 3D radiation on cloud evolution (Photo courtesy of gordonr@iafrica.com) Steven Dobbie, University of Leeds dobbie@env.leeds.ac.uk Leeds, April 6

Research Activities Dr Sat Ghosh - Diffusivity of H2O (FIRE II) - Mid-lat SH cirrus: Emerald I case – microphysics - Radiative forcing of multi-component aerosol Dr John Marsham - Mid-lat NH cirrus: Chilbolton case – effects of shear - Initialisation, validation, resolution, 3D runs, fall velocities dobbie@env.leeds.ac.uk

Research Activities Adrian Hill - Semi-direct/indirect effects: effect of soot on clouds. Clare Allen - Tropical cirrus: evolution of anvil with emphasis on sensitivity to outflow region and ice nuclei. Gourihar Kulkarni (GK) - Nucleation chamber/microphysics. dobbie@env.leeds.ac.uk

Research Activities My activities - Growth and optical properties of seasalt aerosols (direct eff) - Treatment of overlap and inhomogeneity for radiation - 3D radiative effects on cloud evolution dobbie@env.leeds.ac.uk

Clouds in GCMs Diagnostic Prognostic ice/liquid water content ‘Statistical’ Prognostic schemes (eg Tompkins 2002). Plane parallel homogeneous (PPH) clouds introduce bias (Cahalan 1994, Barker et al 1998 and Larson et al 2001) dobbie@env.leeds.ac.uk

Motivation Climate is very sensitive to cirrus Cirrus are poorly understood (GCSS WG2) Inhomogeneity and radiative properties dobbie@env.leeds.ac.uk

Motivation Observed cloud structure (1, 2-3, 5 km) Smith and Jonas, ‘96, ‘97 Quante et al., ‘96 Demoz et al., ‘96 Gultepe and Starr, ‘95 Starr et al., ‘92 Starr and Cox, ‘85 GCM sub-grid inhomogeneity treatment dobbie@env.leeds.ac.uk

The Large Eddy Model The LEM: 2D mode (100 km domain) 100 m horizontal resolution, 125 m vertical resolution 3 phase microphysics with dual moment ice/snow Rigid top and bottom Periodic lateral boundary conditions Fu-Liou radiation model dobbie@env.leeds.ac.uk

Initial Profiles UK LES CRM dobbie@env.leeds.ac.uk

IWC Time Evolution dobbie@env.leeds.ac.uk

Cellular Development dobbie@env.leeds.ac.uk

Length-scales of inhomogeneity dobbie@env.leeds.ac.uk

Inhomogeneity and Cloud Depth dobbie@env.leeds.ac.uk

Spectral Dependence dobbie@env.leeds.ac.uk

Radiative Heating Profiles dobbie@env.leeds.ac.uk

Cloud Lifetime dobbie@env.leeds.ac.uk

Radiation and Latent Stability Numbers dobbie@env.leeds.ac.uk

Instability (Rad. Influenced) dobbie@env.leeds.ac.uk

Instability (No Rad.) dobbie@env.leeds.ac.uk

Previous studies Wide range of results between cirrus models even for simple idealised case studies (Starr et al 2000). There are few comparisons of CRM results with observations for ice clouds. In existing comparisons modelled inhomogeneity can be much less than observed (eg Benedetti and Stephens 2001) dobbie@env.leeds.ac.uk

Observed and LEM profiles dobbie@env.leeds.ac.uk

Ice Water Contents (IWCs) Radar LEM dobbie@env.leeds.ac.uk Approx. 70 - 180 km

Effects of shear on sub-grid variability 9.25 km 8.25 km Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical). Ice water content Total Water Content dobbie@env.leeds.ac.uk

Effect of shear on vertical correlation of IWC dobbie@env.leeds.ac.uk

Motivation Question: By neglecting 3D radiative transfer, are we missing an important influence on cloud evolution or can it be neglected? dobbie@env.leeds.ac.uk

PPA and ICA/IPA Radiaton dobbie@env.leeds.ac.uk

Monte Carlo Radiation dobbie@env.leeds.ac.uk

Radiative smoothing scale dobbie@env.leeds.ac.uk

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Inhomogeneous cirrus layers MC IPA dobbie@env.leeds.ac.uk

Inhomogeneous cirrus layers Rmc=0.219 R4s=0.225 Rnr=0.196 dobbie@env.leeds.ac.uk

Inhomogeneous cirrus layers dobbie@env.leeds.ac.uk

Finite cirrus layer MC IPA dobbie@env.leeds.ac.uk

Finite cirrus layer Rmc=0.423 R4s=0.396 Rnr=0.372 dobbie@env.leeds.ac.uk

Finite cirrus layer dobbie@env.leeds.ac.uk

Summary/Conclusions Radiative effects are important for cirrus Inhomogeneous stratiform layers: 2-3% Finite, inhomogeneous cirrus clouds: 6-7% dobbie@env.leeds.ac.uk

Further Work Realistic clouds (Chilbolton,FIREII, Emerald1, Crystal Face) with various geometries Longer duration simulations Quantify effects on cloud microphysics Effect for PDFs? Understand 3D radiation in presence of other effects, like shear Other cloud types dobbie@env.leeds.ac.uk

[G. Heymsfield] Tropical Anvils dobbie@env.leeds.ac.uk

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Inhomogeneous layer dobbie@env.leeds.ac.uk

Finite cirrus layer dobbie@env.leeds.ac.uk

16 July C-F Anvil Mission P. Lawson D. Baumgardner A. Heymsfield dobbie@env.leeds.ac.uk

Observations:. Supersaturation Frequently Observed in the Upper Observations: Supersaturation Frequently Observed in the Upper Troposphere [J. Smith, A. Anderson, P. Bui] We observe supersaturation both in clear air and in the presence of cirrus. dobbie@env.leeds.ac.uk

Observed and LEM profiles dobbie@env.leeds.ac.uk Reading, Dec 8

Microphysics dobbie@env.leeds.ac.uk

Effects of shear on sub-grid variability 9.25 km 8.25 km Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical). Ice water content Total Water Content dobbie@env.leeds.ac.uk

Effects of shear on sub-grid variability 6.5 km 4.7 km Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical). Ice water content Total Water Content dobbie@env.leeds.ac.uk

Effect of shear on vertical correlation of IWC dobbie@env.leeds.ac.uk

Conclusions Further Work Distributions of modelled IWCs and total water contents are well described by beta functions. Shear tends to decrease the variance in IWC and total water contents. The decorrelation of IWC with height is initially linear (as suggested in Hogan and Illingworth 2002). At larger vertical separations correlations tend to be zero for zero shear and are more complex for inhomogenous clouds with large wind-shears. Further Work Improve the initialisation of the LEM. Study a better observed case (with aircraft observations). (Acknowledgements: Robin Hogan, Reading University) dobbie@env.leeds.ac.uk