Iterative Iterative surrogate cloud fieldssurrogate cloud fields

Victor VenemaVictor Venema

Amplitude distributionAmplitude distribution Amplitude (LWP, LWC, Amplitude (LWP, LWC, ) alone is ) alone is

already good: See Independent Pixel already good: See Independent Pixel Approximation (IPA)Approximation (IPA)

Especially very important are the cloud Especially very important are the cloud free portionsfree portions

Together with power spectrum it also Together with power spectrum it also ‘defines’ the structure‘defines’ the structure

Measured power spectrumMeasured power spectrum Fractal power spectrum?Fractal power spectrum? Measured power spectrumMeasured power spectrum

– Scale breaksScale breaks– WavesWaves– ……

Satellite pictures: Eumetsat

Iterative algorithmIterative algorithm

Add an dimensionAdd an dimension Assume isotropyAssume isotropy Rotate and scale power spectrumRotate and scale power spectrum

1000 2000 3000 4000 5000 6000 7000 80000

100

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Time (s)

LWP

(gr

/m2 )

Time (s)

Tim

e (s

)

2000 4000 6000 8000

1000

2000

3000

4000

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7000

8000 0

100

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3D surrogate clouds3D surrogate clouds

Time [hr] UT

Hei

ght

[km

] LWC template [kg/m3]

10.5 11

1.4

1.6

1.8

2

2.2

0

0.1

0.2

0.3

0.4

0.5

LWC Surrogate

0 2 4 60

2

4

6

0

2

4

6

0 2 4 61.5

2

Reff

Surrogate

0 2 4 60

2

4

6

0

2

4

6

0 2 4 61.5

2

Time [hr] UT

Hei

ght

[km

]

LWC template [kg/m3]

13.2 13.41

1.5

2

0

0.5

1

1.5

LWC Surrogate

0 2 4 6 80

2

4

6

8

0

2

4

6

8

0 2 4 6 81

1.52

Reff

Surrogate

0 2 4 6 80

2

4

6

8

0

2

4

6

8

0 2 4 6 81

1.52

Time [hr] UT

Hei

ght

[km

]

LWC template [kg/m3]

7 7.5

0.5

0.6

0.7

0.8

0.9

0

0.5

1

1.5

LWC Surrogate

0 5 100

5

10

0

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10

0 5 10

Reff

Surrogate

0 5 100

5

10

0

5

10

0 5 10

Time [hr] UT

Hei

ght

[km

]

LWC template [kg/m3]

9 9.5

0.4

0.6

0.8

0

0.2

0.4

0.6

LWC Surrogate

0 5 100

5

10

0

5

10

0 5 100.40.60.8

Reff

Surrogate

0 5 100

5

10

0

5

10

0 5 100.40.60.8

Validation surrogate cloudsValidation surrogate clouds 3D LWC fields from LES modelling3D LWC fields from LES modelling Make surrogates from their statisticsMake surrogates from their statistics Calculate radiative propertiesCalculate radiative properties

– RadiancesRadiances– IrradiancesIrradiances– Actinic fluxesActinic fluxes

Compare themCompare them

Surrogate stratocumulusSurrogate stratocumulusTemplatesTemplates SurrogatesSurrogates

Reflectance template and Reflectance template and surrogate stratocumulussurrogate stratocumulus

0.3 0.4 0.5 0.6 0.7

0.3

0.4

0.5

0.6

0.7re

flect

ance

sur

roga

te

reflectance template

(a)

Surrogate cumulus - oldSurrogate cumulus - oldTemplatesTemplates SurrogatesSurrogates

Surrogate cumulus – radianceSurrogate cumulus – radiance

0.005 0.01 0.015 0.02

0.005

0.01

0.015

0.02

radiance template cumulus [W m-2 sr-1]

radi

ance

sur

roga

te [W

m-2

sr-1

]

Validation cumulus - newValidation cumulus - new Developed a more Developed a more

accurate Stochastic accurate Stochastic IAAFT algorithmIAAFT algorithm

Surrogates are Surrogates are copies of templatescopies of templates

In practise the bias In practise the bias is likely still there as is likely still there as you cannot measure you cannot measure the power spectrum the power spectrum that accuratelythat accurately

Validation broken cloudsValidation broken clouds

Scanning measurementsScanning measurements Structure maintaining interpolationStructure maintaining interpolation Anisotropic power spectrumAnisotropic power spectrum More samplesMore samples Better Better

decorrelationdecorrelation

Scanning measurementsScanning measurements Scanning Scanning

measurementmeasurement– Amplitude distribution Amplitude distribution – 2D power spectrum2D power spectrum

Force the measured Force the measured values on the spiralvalues on the spiral

Measured: Measured: 16.5 %16.5 %

Scanning measurementsScanning measurements

Surrogate with cloud mask

ConclusionsConclusions IAAFT algorithmIAAFT algorithm

– Full 3D structureFull 3D structure– LWC height profileLWC height profile– Local forcing of measurementsLocal forcing of measurements– FlexibleFlexible

DimensionsDimensions MeasurementsMeasurements Vary the statistics independentlyVary the statistics independently

Validated for Sc and sparse CuValidated for Sc and sparse Cu– Cloud cover > 80%, <20%Cloud cover > 80%, <20%

3D Cloud fields based on the BBC and 3D Cloud fields based on the BBC and BBC2 campaign on the BBC-serverBBC2 campaign on the BBC-server

OutlookOutlook Improve convergence for broken cloudsImprove convergence for broken clouds Validate for broken cloudsValidate for broken clouds Iterative wavelet surrogatesIterative wavelet surrogates Constrained surrogatesConstrained surrogates Sebastián Gimeno García: 2D and 3D Sebastián Gimeno García: 2D and 3D

radiative transferradiative transfer Sebastian Schmidt: 3D surrogates from Sebastian Schmidt: 3D surrogates from

in situ measurementsin situ measurements 3D Surrogates from scanning 3D Surrogates from scanning

measurementmeasurement

Comparison cloud generatorsComparison cloud generators Reviewer: “It is not clear why this technique is an

improvement over simpler approaches.”

IAAFT methodIAAFT method Cumulus fields (Evans; structure of a binary mask)Cumulus fields (Evans; structure of a binary mask)

CALBAUTAIR (Schreirer and Schmidt)CALBAUTAIR (Schreirer and Schmidt) Shift cloud (Schmidt; Los and Duynkerke)Shift cloud (Schmidt; Los and Duynkerke) 2D-2D Ice cloud (Liou et al.)2D-2D Ice cloud (Liou et al.)

tdMAP (tdMAP (A. Benassi, F. Szczap, et al.)A. Benassi, F. Szczap, et al.) Multi-fractal cloudsMulti-fractal clouds Bounded Cascade and other fractal cloudsBounded Cascade and other fractal clouds Fourier methodFourier method

– SITCOM (F. di Giuseppe; 2D structure)SITCOM (F. di Giuseppe; 2D structure)– Ice clouds (R. Hogan, S. Kew; 2.5D structure)Ice clouds (R. Hogan, S. Kew; 2.5D structure)

3SPL3SPL3SP3SP

3_PL3_PL2__L2__L2__L2__L

2SP_2SP_2SP_2SP_2S__2S__2S__2S__

Bounded CascadeBounded Cascade It is a power spectral method just as It is a power spectral method just as

the Fourier methodthe Fourier method The amplitude distribution is fixed, The amplitude distribution is fixed,

‘Log-normal like’‘Log-normal like’ Why take block functions?Why take block functions? At least for the Fourier method there is At least for the Fourier method there is

a large amount of literaturea large amount of literature But Bounded Cascade clouds are But Bounded Cascade clouds are

fractals!!fractals!!

1D Iterative LWP surrogates1D Iterative LWP surrogates

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Time (s)

LWP

(gr

/m2 )

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Time or space

LWP

or

LWC

1D Iterative LWP surrogates1D Iterative LWP surrogates

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Time (s)

LWP

(gr

/m2 )

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500

Time or space

LWP

or

LWC

0 500 1000 1500 2000 2500 3000 35000

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Number

LWP

(gr

/m2 )

MeasuredSurrogate

10-3

10-2

10-1

10-5

100

105

k (Hz)

Pow

er

MeasuredSurrogate

2D Iterative LWP surrogates2D Iterative LWP surrogates

1000 2000 3000 4000 5000 6000 7000 80000

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Time (s)

LWP

(gr

/m2 )

Time (s)

Tim

e (s

)

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Conclusions and outlookConclusions and outlook Improve convergenceImprove convergence Cumulus fields are very intermittantCumulus fields are very intermittant

– Smooth clear sky partSmooth clear sky part– Structured cloudy partStructured cloudy part

Maybe iterative wavelet surrogates Maybe iterative wavelet surrogates would converge bettterwould converge bettter

Evolutionary search algorithm doesn‘t Evolutionary search algorithm doesn‘t get easily stuck in local minimaget easily stuck in local minima