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Motivation Experimental Description Results Summary

Aerosol Removal and Cloud Collapse Accelerated by Supersaturation Fluctuations with a Positive Feedback in Turbulent Cloud: a Cloud-Chamber Study

Kamal Kant Chandrakar

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

and Π-Chamber Group

Michigan Technological University

Acknowledgment : NSF, NASA Earth and Space Science Fellowship

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Motivation Experimental Description Results Summary Aerosol Feedback

Source: NASA Visible Earth-MODIS image

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Motivation Experimental Description Results Summary Aerosol Feedback

Goren and Rosenfeld JGR 2015

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Motivation Experimental Description Results Summary Steady-State Turbulent Cloud

The Π- Chamber

CLOUD LAB CLOUD LAB

Understanding Cloud–Turbulence Interactions Understanding Cloud–Turbulence Interactions

TARGETED OBSERVATIONS TROPICAL SST BIASES DECADAL PREDICTION

Volume 97 Number 12 December 2016

Chang et al. BAMS 2016

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Motivation Experimental Description Results Summary Steady-State Turbulent Cloud

The Π- Chamber

Wet Boundaries

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Motivation 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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Motivation Experimental Description Results Summary Steady-State Turbulent Cloud

Supersaturation in the chamber: Idealized vs Reality

Water vapor fmux to the side wall is signifjcant: nearly 1/3 reduction in s with a saturated side wall at mean temperature

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) 1 0.8 0.6 0.4 0.2

Z*

0.2 0.4 0.6 0.8 1

T* [7 / 18] Kamal Kant Chandrakar Turbulence Induced Aerosol Feedback

Motivation Experimental Description Results Summary Steady-State Turbulent Cloud

Supersaturation in the Chamber: Idealized vs Reality

Residual: Dmode ≈ 110 nm → sc = 0.1%

Note: The apparent difgerence in area under the PDFs is a result of linear size binning displayed in a semilog plot. 101 102

Dp [nm]

0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

PDF Interstitial Residual

Chandrakar et al. GRL 2017

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing

Droplet Size Distribution at Steady-State

2 4 6 8 10 12 100 200 300 400 500 600 d [µm] 10 20 30 40

PDF

0.05 0.1 0.15 ˙ na = 1515/cm3/min ˙ na = 12/cm3/min ˙ na = 4/cm3/min ˙ na = 2/cm3/min ˙ na = 1/cm3/min

Chandrakar et al. PNAS 2016

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing

Stochastic Condensation Growth

ds(t) =      so − s τt

mixing to so

− s τc

• droplet growth

     dt + (2σ2

s0dt

τt )1/2 η(t)

• fmuctuation

Condensation Growth: dr2 dt = 2ξs, dσ2

r2

dt = 4ξs′r2′

Chandrakar et al. PNAS 2016, JAS 2018

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing

Turbulent Induced Broadening

¯ s = soτs τt ; σ2

s = σ2 s0τs

τt σr2 ∝ s′r2′ → σs0τs τt t1/2 τs :

1 τs = 1 τt + 1 τc

τt : Turbulence correlation time

(fjxed)

τc : Phase relaxation time,∝

1 ¯ n¯ r

(controlled by aerosol injection)

τs [s]

0.6 0.8 1 1.2 1.4 1.6 1.8 2

σr

2 [µm2]

10 20 30 40 50 60 70

τc [s]

50 100

σr

2 [µm2]

20 40 60 80

Chandrakar et al. PNAS 2016

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing Continental Polluted Cloud Slow Aerosol Decay and Cloud Droplet Growth Suppressed Droplet Loss Low Aerosol Activation Rate Faster Aerosol Decay and Cloud Growth

C l

• u

d C

• l

l a p s e

Faster Droplet Loss High Aerosol Activation Rate Stage-I : Suppressed

Supersaturation Mean and Fluctuation

Stage-II : Faster

Supersaturation Mean and Fluctuation Recovery

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing 102 104 nd [cm-3] 10 20 d [ m] 50 100 150 t [min] 5 10 15

c [s]

100 105

na[cm-3]

2 4

r [ m]

Chandrakar et al. GRL 2017

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing

50 100 150 200 250

Da [nm]

12 14 16 18 20 22 24 26 28

a [min]

50 100 150

t [min]

• 6
• 4
• 2

2 4 6 8

ln(dNbin)

Chandrakar et al. GRL 2017

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing 50 100 150 200 250 300

t [min]

102

nd [cm-3]

6 8 10 12 14 16 18

d [ m]

50 100 150 200 250 300

t [min]

0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25

s [%]

5 10 15 20

S-S(t=0)

10-3

Chandrakar et al. GRL 2017

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Motivation Experimental Description Results Summary Turbulence Induced Broadening Turbulence Induced Cloud Cleansing Continental Polluted Cloud Slow Aerosol Decay and Cloud Droplet Growth Suppressed Droplet Loss Low Aerosol Activation Rate Faster Aerosol Decay and Cloud Growth

C l

• u

d C

• l

l a p s e

Faster Droplet Loss High Aerosol Activation Rate Stage-I : Suppressed

Supersaturation Mean and Fluctuation

Stage-II : Faster

Supersaturation Mean and Fluctuation Recovery

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Motivation Experimental Description Results Summary Summary

Summary

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)

d [µm] 10 20 30 40 PDF 0.05 0.1 0.15 ˙ na = 1515/cm3/min ˙ na = 12/cm3/min ˙ na = 4/cm3/min ˙ na = 2/cm3/min ˙ na = 1/cm3/min τs [s] 0.6 0.8 1 1.2 1.4 1.6 1.8 2 σr

10 20 30 40 50 60 70 τc [s] 50 100 σr

20 40 60 80 102 104 nd [cm-3] 10 20 d [ m] 50 100 150 t [min] 5 10 15 c [s] 100 105 na[cm-3] 2 4 r [ m] 50 100 150 200 250 Dp [nm] 10 15 20 25 30 a [min] 50 100 150 t [min]

• 6
• 4
• 2

Cloud form via isobaric mixing in a turbulent moist Rayleigh-Bénard convection. Stochastic theory and experiments suggest: σ2

s = σ2

soτs

τt

and σr2 ∝ s′r2′ → σs0τs

τt t1/2.

Cloud cleansing enhanced through supersat- uration fmuctuations: a positive feedback.

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Motivation Experimental Description Results Summary Summary

Thank You

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