Relationship Between Cloud Droplet Effective Radius and Cloud Top Height for

Deep Convective Clouds in CloudSat Data Product

Satoshi Suzuki, Shinta Seto, and Taikan OkiInstitute of Industrial Science, the University

of Tokyo

Background: Aerosol Convection Invigoration Effect Hypothesis

Rosenfeld et al. (2008)

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Background: Aerosol Convection Invigoration Effect Hypothesis

Aerosol concentration

Cloud droplet radius

Cloud top height

Ex) Nakajima et al. (2001)

Purpose: Examine Cloud droplet radius - Cloud top height relationship

Ex) Koren et al. (2010)

Data: CloudSat 2B-CWC-RVOD (Dec. 2006-Feb. 2007)

Cloud Top Height >5000m

Cloud Base<1500m

50km (Independent data)

Cloud top height: highest bin with value

Cloud droplet effective radius (liquid only)

Cloud droplet effective radius↓

Convection↑ Cloud top height↑ 4

Conditions of the clouds to be analyzed

Geographical Distribution of Clouds Matching the Condition

5Cloud top height [m]

Average profile for each cloud top height

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Average profile for each cloud top height

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Cloud droplet effective radius - Cloud top height relationship

Cloud droplet effective radius↓

Cloud top height↑ 8

Radar Reflectivity Factor and Cloud Top Height

Radar reflectivity is lower for lower clouds => correct attenuation calculation is needed for the negative relationship to appear 9

Droplet Radius – Cloud Top Height Relationship for clouds without precipitation flag (dBZe<-15)

10Significant negative correlation still appears

Variation of the relationship by surface temperature

Rosenfeld et al. (2008) suggested freezing causes clouds to become invigorated.

Freezing Level

Invigoration No Invigoration Low Invigoration

High Temperature Low Temperature

Variation of the relationship by surface temperature

Cloud top >5000m　　⇓>1600mCloud base < 1500m　　⇓<1000m

50km (Independent data)

Cloud top height

Cloud droplet effective radius

To see the effect of freezing, lower clouds are also included in the analysis.

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Freezing Level

Lower clouds do not show negative correlation

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Cloud droplet effective radius - Cloud top height relationship

Surface temperature 30 – 40 deg C

No negative correlation

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Surface Temperature 10 – 20 deg C

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Negative correlation appears in clouds with lower cloud top heights

Freezing Level

Surface Temperature 0 – 10 deg C

By moist adiabatic lapse rate, in most cases, altitude of 2000m should be below 0 deg C

A mechanism other than freezing? 16

Freezing Level

Another Hypothesis by Lee et al. (2010)

Higher aerosol concentration

Smaller Cloud droplet effective radius (Larger surface area)

Larger Evaporation rate

Stronger downdraft, gust front

Stronger Convection17

In clouds with cloud top heights lower than 3000 m, gust fronts do not form?

Conclusions• By analyzing CloudSat 2B-CWC-RVOD product,

negative correlation is found between cloud droplet effective radius and cloud top height for deep clouds

• The negative correlation supports the hypothesis that aerosols are invigorating deep clouds

• Negative correlation do not appear for clouds with low cloud top heights

• When surface temperature is high, the threshold altitudes for negative correlation becomes higher

• Attenuation calculation has a large role in determining the sign of the relationship

• Analysis of clouds with low reflectivity only also shows the relationship is significantly negative

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Thank you for your kind attention!

The authors would like to acknowledge the CloudSat Data Processing Center at CIRA/Colorado State University for providing data products, Environment Research and Technology Development Fund (S-8) of the Ministry of the Environment, Japan, KAKENHI(22760365), JSPS, Japan, and IGARSS 2011 for their support to this work and presentation.