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CIMSS/SSEC Effort on the CIMSS/SSEC Effort on the Fast IR Cloudy Forward Model DevelopmentFast IR Cloudy Forward Model Development

A Fast Parameterized Single Layer Infrared A Fast Parameterized Single Layer Infrared Cloudy Forward Model Status and FeaturesCloudy Forward Model Status and Features

Hung-Lung Allen Huang & ColleaguesCIMSS/SSEC, Univ. of WI-Madison

& Ping Yang, Texas A&M

2nd Workshop on Advanced High Spectral Resolution Infrared Observations

Ravello, Italy 24-26 May 2004

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UW Hyperspectral Sounder Simulator & Processor (HSSP) Simulator – Clear, Clouds, and Haze Radiances

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Q u ic k T im e ™ a n d aG ra p h ic s d e c o m p re s s o r

a re n e e d e d to s e e th is p ic tu re .

I0T(µ)a1(µ)

a0Clouds

The Surface

I0

I1

I1

Icld(µ)a1(µ) (µ)a1(µ)I1

a1

Itop()I0T()a1() Iclda1() I1 I1()a1()

Computing techniques:• FDTD: the finite-difference time-

domain method • IGOM: Improved geometric optics

method • SSPM: Stretched scattering potential

methodComposite method: A combination of FDTD or

other method (such as the T-matrix) with the weighted summation of approximate solutions for obtaining the single-scattering properties for small size parameters to large size parameters.

Parameterization:• Based on the effective size of in-situ

particle size distribution

Sensitivity studyEffective particle sizeVisible optical thickness

Simultaneous retrieval of the optical thickness and effective particle size of cirrus clouds

UW HSSP Cloudy Fast Model Development

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Radiative Transfer Approximation

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2

3

4

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6

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98

99

100

101

Pc

1100

0

Ps

Layer#

Pressure (hPa)

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c

s

I

s

c

0

gaseoustrans. / OD

II

I

I I RRc

I c

Icc

I I0 c + Icc + I + I RRc

Cloud Reflectivity and Transmittance Parameterization

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The typical ice crystal habits for tropical (left), midlatitude (middle), and polar (right) cirrus cloud system.

Data courtesy of A. Heymsfield and his colleagues (NCAR), S. Warren (University of Washington), and P. Lawson (SPEC).

Ice Crystal Habits

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Ice Crystal Single-Scattering Property Database

•Shapes of ice crystalsAggregates, solid hexagonal columns, Spheres, Bullet-rosettes, Droxtals, Hollow columns, Plates, and Spheroids

•Wavelengths: 49 Wavelengths from 3.08 µm to 100 µm•Size bins: 38 Size bins from 2 µm to 3100 µm in terms of particle maximum dimension

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Refractive index(real and imaginary parts) of ice

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0.2

0.4

0.6

0.8

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100 1000 4000

Imag

inar

y P

art o

f Ref

ract

ive

Inde

x

Wavenumber (cm-1)

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1.2

1.4

1.6

1.8

2

100 1000 4000R

eal P

art o

f Ref

ract

ive

Inde

xWavenumber (cm-1)

The circles indicate the wavelengths where the scattering computations were carried out.

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Ice Crystal Single-Scattering Property Computation Methods

• The finite difference time domain (FDTD) code (Yang and Liou, 1996a, Yang et al. 2000, 2004) for small particles with size parameters up to 20.

• The T-matrix method (Mishchenko 1989) for small spheroids.

• A combination of an improved geometric optics method (IGOM) (Yang and Liou, 1996b) and the method of Lorenz-Mie Equivalent spheres (equivalence in volume for plates and hollow columns, or in terms of the ratio of volume to project area for other shapes) for medium to large particle sizes.

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