Infmuence of Turbulent Fluctuations on Cloud Droplet Size Dispersion - - PowerPoint PPT Presentation

Introduction Experimental Description Results Summary

Infmuence of Turbulent Fluctuations on Cloud Droplet Size Dispersion and Aerosol Indirect Efgects

Kamal Kant Chandrakar

• Dr. Will Cantrell, and Dr. Raymond A. Shaw

Π-Chamber Group Michigan Technological University

Acknowledgment : NSF, NASA Earth and Space Science Fellowship

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

Source: NASA Earth Observatory

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

Efgective Radius Parameterization

re = ∫ r3n(r)dr ∫ r2n(r)dr ≈ [ 3 L 4 π ρl nd k(d, γ) ]1/3 L: liquid water content; n : droplet number density; d ≡ σr/¯ r : relative dispersion γ : skewness; k = r3/r3

e and d ↑ ⇒ k ↓

Pontikis & Hicks 1992

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

A linear relation between r3 and r3

e:

Marine Cloud Continental Cloud

Martin et al. JAS 1998

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

k = r3/r3

e and d ↑ ⇒ k ↓

τ ∝ n1/3

d

X Twomey Efgect Lifetime Efgect Dispersion Efgect

Pontikis & Hicks 1992

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

k = r3/r3

e and d ↑ ⇒ k ↓

τ ∝ n1/3

d

X L2/3 X Twomey Efgect Lifetime Efgect Dispersion Efgect

Pontikis & Hicks 1992

[5 / 16] Kamal Kant Chandrakar Turbulence Induced Aerosol Efgects

Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

k = r3/r3

e and d ↑ ⇒ k ↓

τ ∝ n1/3

d

X L2/3 X k1/3 ∆Z Twomey Efgect Lifetime Efgect Dispersion Efgect

Pontikis & Hicks 1992

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

Atmospheric Observations

Aerosol ↑ ⇒ d ↓ (Enhanced indirect efgects):

Miles et al. 2000; Lu et al. 2007,2012,2013

Aerosol ↑ ⇒ d ↑ (Suppressed indirect efgects):

Martin et al. 1998; Miles et al. 2000; Liu and Daum 2002; Peng and Lohmann 2003 ;Pawlowska et al. 2006; Pandithurai et al. 2012

Aerosol ↑ ⇒ d ⇒ constant or unclear trend:

Miles et al. 2000; Zhao et al. 2006; Lu et al. 2008; Tas et al. 2015

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

Adiabatic Condensation Approach

dr dt ∝ s r Droplet size dispersion decreases with time Aerosol ↑ ⇒ s ↓ ⇒ decreased narrowing: a positive correlation between d and Aerosol

Yum and Hudson 2005; Liu et al. 2006; Peng et al. 2007

Limitations: Small droplet size dispersion Supersaturation fmuctuations are not included

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Introduction Experimental Description Results Summary Aerosol Indirect Efgects Theoretical Framework

Stochastic Condensation

dr2 dt = 2 ξ (¯ s + s′) r2 ∝ ¯ s t σr2 ∝ σs0τ 1/2

t

(1 + C ¯ r nd τt)t1/2 d ∝ σso so t−1/2

¯ s and s’: Supersaturation mean and fmuctuation σs: std of supersaturation fmuctuations nd: Droplet concentration τt: Turbulence correlation timescale The relative dispersion depends on supersaturation mean and fmuctuation forcing, as well as, on the droplet lifetime. Chandrakar et al. PNAS 2016, JAS 2018

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Introduction Experimental Description Results Summary Steady-State Turbulent Cloud

Turbulent Mixing Cloud Formation in the Π-Chamber

5 10 15 20 25 T [oC] 10 15 20 25 30 pv [mbar] Bottom pv,mix Tmix Top Equilibrium Vapor Pressure, p s(T) ps(Tmix)

cool, humid warm, humid steady aerosol injection cloud droplet activation droplet growth in turbulent environment droplet sedimentation

turbulent convection

low aerosol injection high aerosol injection

a) b)

Chandrakar et al. PNAS 2016

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Introduction Experimental Description Results Summary Efgective Radius Parameterization Aerosol Efgect on Relative Dispersion Autoconversion Timescale

A linear relation between r3 and r3

e:

200 400 600 800 1000 1200 1400 1600 1800 re

3 [ m3]

200 400 600 800 1000 1200 rv

3 [ m3]

60 80 100 120 re

3 [ m3]

60 80 100 rv

3 [ m3]

500 1000 1500 re

3 [ m3]

200 400 600 800 1000 1200 rv

3 [ m3]

k = 0.84 0.1 k = 0.62 0.03 k = 0.66 0.01

Martin et al. JAS 1998

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Introduction Experimental Description Results Summary Efgective Radius Parameterization Aerosol Efgect on Relative Dispersion Autoconversion Timescale

102 103

nd [cm-3]

0.1 0.2 0.3 0.4 0.5

d

Measurement Stochastic Condensation Model

Chandrakar et al. JAS 2018

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Introduction Experimental Description Results Summary Efgective Radius Parameterization Aerosol Efgect on Relative Dispersion Autoconversion Timescale

102 103

nd [cm-3]

0.1 0.2 0.3 0.4 0.5

d

Measurement Stochastic Condensation Model

d ∝ σso so t−1/2 nd ↑ ⇒ d ↓ :

since the average droplet lifetime is an increasing function of nd. Chandrakar et al. JAS 2018

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Introduction Experimental Description Results Summary Efgective Radius Parameterization Aerosol Efgect on Relative Dispersion Autoconversion Timescale

Dispersion efgect enhances the 1st indirect efgect (τ ∝ k1/3):

200 400 600 800 1000 1200 1400 1600 1800

re

3 [ m3]

200 400 600 800 1000 1200

rv

3 [ m3]

60 80 100 120

re

3 [ m3]

60 80 100

rv

3 [ m3]

500 1000 1500

re

3 [ m3]

200 400 600 800 1000 1200

rv

3 [ m3]

k = 0.84 0.1 k = 0.62 0.03 k = 0.66 0.01 500 1000 1500 2000 2500 3000

nd [cm -3] 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 k Measurement Theory

Chandrakar et al. GRL 2018 (in review)

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Introduction Experimental Description Results Summary Efgective Radius Parameterization Aerosol Efgect on Relative Dispersion Autoconversion Timescale

Dispersion efgect enhances the 2nd indirect efgect:

100 101 102 103

nd [cm-3]

100 105 1010 1015

a [h]

Chandrakar et al. JAS 2018

The precipitation timescale (τa ≡ L(dL/dt)−1) signifjcantly decreases in the clean cloud regime.

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Introduction Experimental Description Results Summary Summary

Summary

200 400 600 800 1000 1200 1400 1600 1800 re 3 [ m3] 200 400 600 800 1000 1200 rv 3 [ m3] 60 80 100 120 re 3 [ m3] 60 80 100 rv 3 [ m3] 500 1000 1500 re 3 [ m3] 200 400 600 800 1000 1200 rv 3 [ m3] k = 0.84 0.1 k = 0.62 0.03 k = 0.66 0.01 102 103 nd [cm-3] 0.1 0.2 0.3 0.4 0.5 d Measurement Stochastic Condensation Model 500 1000 1500 2000 2500 3000 nd [cm -3] 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 k Measurement Theory 100 101 102 103 nd [cm-3] 100 105 1010 1015 a [h]

A commonly-used, empirical efgective ra- dius parameterization is observed under con- trolled laboratory conditions. Stochastic theory and experiments suggest: d ∝ σso

so t−1/2; nd ↑ ⇒ t ↑ ⇒ d ↓

Turbulence-induced dispersion efgect infmu- ences the 1st and 2nd indirect efgects (depends on droplet removal).

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Introduction Experimental Description Results Summary Summary

Thank You

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