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Iterative surrogate cloud fields

Iterative surrogate cloud fields. Victor Venema. Amplitude distribution. Amplitude (LWP, LWC, ) alone is already good: See Independent Pixel Approximation (IPA) Especially very important are the cloud free portions Together with power spectrum it also ‘defines’ the structure.

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Iterative surrogate cloud fields

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  1. Iterative surrogate cloud fields Victor Venema

  2. Amplitude distribution • Amplitude (LWP, LWC, ) alone is already good: See Independent Pixel Approximation (IPA) • Especially very important are the cloud free portions • Together with power spectrum it also ‘defines’ the structure

  3. Measured power spectrum • Fractal power spectrum? • Measured power spectrum • Scale breaks • Waves • … Satellite pictures: Eumetsat

  4. Iterative algorithm

  5. Add an dimension • Assume isotropy • Rotate and scale power spectrum

  6. 3D surrogate clouds

  7. Validation surrogate clouds • 3D LWC fields from LES modelling • Make surrogates from their statistics • Calculate radiative properties • Radiances • Irradiances • Actinic fluxes • Compare them

  8. Surrogate stratocumulus Templates Surrogates

  9. Reflectance template and surrogate stratocumulus

  10. Templates Surrogates Surrogate cumulus - old

  11. Surrogate cumulus – radiance

  12. Validation cumulus - new • Developed a more accurate Stochastic IAAFT algorithm • Surrogates are copies of templates • In practise the bias is likely still there as you cannot measure the power spectrum that accurately

  13. Validation broken clouds

  14. Scanning measurements • Structure maintaining interpolation • Anisotropic power spectrum • More samples • Better decorrelation

  15. Scanning measurements • Scanning measurement • Amplitude distribution • 2D power spectrum • Force the measured values on the spiral • Measured: 16.5 %

  16. Scanning measurements Surrogate with cloud mask

  17. Conclusions • IAAFT algorithm • Full 3D structure • LWC height profile • Local forcing of measurements • Flexible • Dimensions • Measurements • Vary the statistics independently • Validated for Sc and sparse Cu • Cloud cover > 80%, <20% • 3D Cloud fields based on the BBC and BBC2 campaign on the BBC-server

  18. Outlook • Improve convergence for broken clouds • Validate for broken clouds • Iterative wavelet surrogates • Constrained surrogates • Sebastián Gimeno García: 2D and 3D radiative transfer • Sebastian Schmidt: 3D surrogates from in situ measurements • 3D Surrogates from scanning measurement

  19. Reviewer: “It is not clear why this technique is an improvement over simpler approaches.” IAAFT method Cumulus fields (Evans; structure of a binary mask) CALBAUTAIR (Schreirer and Schmidt) Shift cloud (Schmidt; Los and Duynkerke) 2D-2D Ice cloud (Liou et al.) tdMAP (A. Benassi, F. Szczap, et al.) Multi-fractal clouds Bounded Cascade and other fractal clouds Fourier method SITCOM (F. di Giuseppe; 2D structure) Ice clouds (R. Hogan, S. Kew; 2.5D structure) 3SPL 3SP 3_PL 2__L 2__L 2SP_ 2SP_ 2S__ 2S__ Comparison cloud generators

  20. Bounded Cascade • It is a power spectral method just as the Fourier method • The amplitude distribution is fixed, ‘Log-normal like’ • Why take block functions? • At least for the Fourier method there is a large amount of literature • But Bounded Cascade clouds are fractals!!

  21. 1D Iterative LWP surrogates

  22. 1D Iterative LWP surrogates

  23. 2D Iterative LWP surrogates

  24. Conclusions and outlook • Improve convergence • Cumulus fields are very intermittant • Smooth clear sky part • Structured cloudy part • Maybe iterative wavelet surrogates would converge bettter • Evolutionary search algorithm doesn‘t get easily stuck in local minima

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