Effects of 3D radiation on cloud evolution Steven Dobbie Univ of Leeds

Motivation Climate - radiative properties and cloud feedbacks Weather - heat and moisture distributions and fluxes Aerosols - distributions and processing Heterogeneous chemistry Satellite retrievals

Motivation Cirrus cloud structure (1, 2-3, 5, 20 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

Clouds in GCMs Prognostic water schemes

More motivation GCSS WG2 (Starr et al 2000)

Research Question What effect does 3D radiation have on the evolution of clouds?

Research Tools LEM (cloud model) MC (3D radiation model)

IWC Time Evolution Rad No-Rad

Scales of inhomogeneity Rad No-Rad

Spectral Dependence

Lifetime

PPA radiative transfer

ICA or IPA

Monte Carlo radiation

Radiative smoothing DZ

Inhomogeneity scale

Layer simulations MC IPA

Layer simulations Rmc=0.219 Rppa=0.225

Layer simulations Wavg IWC

Finite layers MC IPA

Finite simulations Rmc=0.423 Rppa=0.396

Finite simulations Wavg IWC

Discussion

Deep Convection Gerard Devine (Leeds)

Radiative Properties - Reflection +2.7 %

Radiative Properties - Absorption -1.45 %

Summary and Conclusions Radiation drives inhomogeneity in cirrus Inhomogeneous stratiform layers: 2-3% Finite cirrus layers: 6-7% Competing effects Deep convection: 2-3% (domain 250km)

Future work Deep convection case (Toga-Coare) Observations Chilbolton, FIREII, Emerald1, Crystal Face Ensemble of runs Quantify microphysical effects Shear

Thanks: Peter Jonas, John Marsham, NERC Contact: dobbie@env.leeds.ac.uk

Future work [G. Heymsfield]

Stability Numbers

Layer simulations

Finite simulations

Instability (No Rad.)

Inhomogeneous layer

Effect of depth Keep?

Finite cirrus layer

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

Effect of shear on vertical correlation of IWC

Motivation Climate is very sensitive to cirrus Cirrus are poorly understood (GCSS WG2) Inhomogeneity and radiative properties

Instability (Rad. Influenced)

Observed and LEM profiles

Ice Water Contents (IWCs) Radar LEM Approx. 70 - 180 km

Chilbolton Case Study

Radiative Heating Profiles

16 July C-F Anvil Mission P. Lawson D. Baumgardner A. Heymsfield

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.

Observed and LEM profiles Reading, Dec 8

Microphysics

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

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

Effect of shear on vertical correlation of IWC

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)