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A Mie Code for Homogeneous Spherical Particles Application to Optical Properties of Water Clouds. Presented by: Xiong Liu March 19, 2001. Outline. Introduction Development of Mie Code Validation Optical properties of water clouds (UV-MV) Mixture Of Carbon Aerosols in Clouds Summary.

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A Mie Code for Homogeneous Spherical Particles Application to Optical Properties of Water Clouds

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A mie code for homogeneous spherical particles application to optical properties of water clouds

A Mie Code for Homogeneous Spherical ParticlesApplication to Optical Properties of Water Clouds

Presented by: Xiong Liu

March 19, 2001


Outline

Outline

  • Introduction

  • Development of Mie Code

  • Validation

  • Optical properties of water clouds (UV-MV)

  • Mixture Of Carbon Aerosols in Clouds

  • Summary


Introduction

Introduction

  • The globe is covered by clouds ~50% of time. Clouds play an very important role in the earth energy budget balance.

    • SW Cloud forcing: ~ -50 W/m2

    • LW Cloud forcing: 30 W/m2

    • Net Cloud forcing: -20 W/m2

  • Cess et al. [1995] and Ramanthan et al. [1995] reported significant solar absorption by clouds of >=25 W/m2 (global-mean) from observations, which is called cloud absorption anomaly and still remains unexplained.

  • Clouds are usually treated as pure water clouds. In reality, cloud droplets grows from CCN, which might contains some absorbing aerosols such as soot (contains element carbon and organic carbon).


A mie code for homogeneous spherical particles application to optical properties of water clouds

Mie Code

  • Input

  • Wavelength(or size parameter), radius, refractive index, angle bin

  • Output

  • Qext, Qsca, Qabs, Qback, Csca, Cext, Cabs, g, w, S11, S12, S33, S34

  • Mie Coefficient Truncation: nmax =  + 4 0.3333+2

  • Forward recursion for computing qn()

  • Downward recursion for computing Pn(), Pn()

  • N=1.1 |z| +10. If |z| <= 10000.

  • N=1.01 |z| +10. If |z| > 10000.


A mie code for homogeneous spherical particles application to optical properties of water clouds

Mie Code-Equation

an1, an2

Qext, Qsca

Qabs

Qback

g

S1, S2

S11,S12

S33,S34


A mie code for homogeneous spherical particles application to optical properties of water clouds

Validation


A mie code for homogeneous spherical particles application to optical properties of water clouds

Validation-Scattering Matrix


A mie code for homogeneous spherical particles application to optical properties of water clouds

Homework Plot 1


A mie code for homogeneous spherical particles application to optical properties of water clouds

Homework Plot 2


A mie code for homogeneous spherical particles application to optical properties of water clouds

Homework Plot 3


A mie code for homogeneous spherical particles application to optical properties of water clouds

Optical Properties of Water Clouds (1)

  • Refractive Index (HITRAN)

  • UV-MW, 90 wavelengths. Resolution is very coarse.

  • No size distribution is used. [Hu and Stammnes, 1993].

  • Cloud Radius = 10um [Han et al., 1994].

  • In UV,VIS, NIR, g, w, Qext, doesn’t change much. Qabs is very small until 1.5 um.

  • Qabs becomes more important at Thermal Infrared, and dominates Qext at Far IR and MW.

  • When lamda >=100um, Qext, g, w, Qabs start to decrease exponentially with lamda.

  • MW is suitable for terrestrial remote sensing (penetrate clouds, all weather).


A mie code for homogeneous spherical particles application to optical properties of water clouds

Optical Properties of Water Clouds (2)


A mie code for homogeneous spherical particles application to optical properties of water clouds

Optical Properties of Water Clouds (3)

Retrieve Optical Thickness

Retrieve Droplet Radius


A mie code for homogeneous spherical particles application to optical properties of water clouds

Mixture of Carbon-Containing Aerosols in Clouds

(Radius =10 um)

0.99790

0.99907

0.9999996


A mie code for homogeneous spherical particles application to optical properties of water clouds

Mixture of Carbon-Containing Aerosols in Clouds

(Radius =10 um)

  • Assume a cloud of optical thickness 100.

  • ppbv Absorption Optical Thickness

  • 0 100 X 4 X10-7 = 4X10-5

  • 10 100 X 1 X10-6 =0.0001

  • 100 0.001

  • 1000 0.01

  • 10000 0.1

BRDF


A mie code for homogeneous spherical particles application to optical properties of water clouds

Summary

  • Mie Code works pretty well except for the direct expansion to obtain the absorption extinction.

  • Optical properties of clouds largely dependent on wavelengths. From UV to 1.5 um, g (~1) and w (~0.86) doesn’t change much. Qext, g, w, Qabs start to drop exponentially when wavelength is larger than 100 um. In MW, g, w, and Qext, Qabs drops to essentially zero.

  • At 0.63um, w almost don’t change with cloud droplet radius. At 3.7um, w drops from 0.98 to 0.73.

  • At 0.55 um, single scattering albedo drops from 0.9999996 to 0.9990 by mixing with soot of 10000 ppbv, approximately dropping one 9 for increasing one order of carbon.


A mie code for homogeneous spherical particles application to optical properties of water clouds

Thank you !


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