Aerosol Cloud Climate Interactions : Outstanding Issues

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Aerosol Cloud Climate Interactions
Outstanding Issues V Ramanathan Scripps
Institution of Oceanography University of
California at Sand Diego October 8,
2007 Aerosol-Cloud-Climate-Specialist workshop,
NCAR,Boulder, Colo
To start our discussion, let us start with an
unanswered, but a fundamental question in
Climate dynamics Why is the Planetary Albedo
29(-1.5) ? Ref http//www-ramanathan.ucsd.edu
.html see Global Albedo Project
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70
Ramanathan 2006
200 Wm-2 700K
650 Wm-2
29
341 Wm-2
240 Wm-2 288 K
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150 Wm-2
125 Wm-2 220 K
http//us.st11.yimg.com/us.st.yimg.com/I/ spaceima
ges_1921_2685747
http//www.solarviews.com/raw/venus/venusvis.gif
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Ref Stephens, 1978
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Remarkable Stability of Planetary Albedo as per
GCMs
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• Fundamental Issues
• A. Radiative Forcing Climate (Progress limited
  to water clouds)
• Aerosol-Radiative interactions (direct
  Rad-forcing)
• Aerosol-Cloud-Radiative Interactions
• (indirect and
  semi-direct Radiative-forcing)
• iii) Aerosol_Radiative Forcing large scale
  dynamics and
• hydrological
  cycle interactions
• B. Thermodynamic Forcing Climate (Limited
  progress Rosenfeld, Andrea, ..)
• iv) Aerosol-cloud-precipitation interactions
  (thermodynamic forcing)
• v) Aerosol_Thermo dyn forcing large scale
  dynamics and
• Hydrological cycle interactions
• C. Radiative-Thermodynamic Forcing Climate
  (non-existent)

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Issues that require intense efforts Aerosols
Role of following in the nucleation process i)
Organics ii) Marine biota (primary
and secondary) iii) Sea Salt
iv) Dust-soot mixtures Aerosol-Cloud
(Radiative Thermodynamic Forcing)
Mixed and Ice Phase Clouds Albedo
Regulation Size spectrum of clouds dependence
of albedo on size Climate Interactions Spatial
temporal Scales of latent heat release and
radiative heating
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Question for the coming decades Will a warmer
planet become more cloudy and rescue us from
overheating?
Ramanathan et al, Science 1989 Harrison et al,
1990
Micro organisms and plants influence the
brightness of clouds!!
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Project Atmospheric Brown Cloud-Asia
Ramanathan, Chair H. Rodhe, Vice
Chair CHINA Shi Guang-Yu, Zhang YuanHang
JAPAN Hajime Akimoto, Teruyuki
Nakajima INDIA P.K. Pachauri, A.P.
Mitra KOREA K.R. Kim, S.C. Yoon EUROPE
P. J Crutzen, M Lawrence S. Fuzzi H.
Rodhe USA G. R. Carmichael J Schauer WMO
Leonard A. Barrie Secretariat UNEP, Bangkok (S
Shrestha M. Iyngara)
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Warming Trends in Asia amplified by brown cloud
solar absorption Ramanathan, Ramana, Roberts,
Corrigan, Chung and Winker, Nature, 448, 575-578,
2007.
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Worldwide Brown Clouds Ramanathan and Ramana,
2002 Data from Kaufman et al 2001
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Based on Chemical Analysis of Filters, size
distribution, Column AOD over the Indian Ocean
from C-130 aircraft surface, ships satellites


Uncertainty lt - 4
Ramanathan et al, JGR, 2001
Plate 8
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Scattering (Cooling)
Absorption (Column Warming)
Cloud Evaporation (Warming)
Absorption (Atmospheric Warming)
Cloud Seeding (Cooling)
Suppression of Rain increase of life time .
Cooling Vertical redistribution of latent and
radiative heating
Dimming of Surface Surface Cooling
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Surface Dimming Atmospheric Heating by Brown
Clouds 2000-2003
Chung, Ramanathan, Kim, Podgorny,2005
ltAgt3 W/m2
Greenhouse Forcing 3 W/m2 Brown Cloud
Masking -1.5 (-50) W/m2
ltSgt-4.5 W/m2
Ramanathan 2007
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Unmanned Aereal vehicles A New tool to observe
Human Impacts
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MAC Campaign Aerosol Observations. Corrigan,
Roberts, Ramana and Ramanathan, ACPD 2007
AOD Week-1
AOD-Weeks 2 3
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Closure with optical depth measurements from
CIMEL Corrigan et al, 2007 Ramana et al, 2007
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Vertical Heating Rates Ramanathan et al, Nature,
2007
Difference Heating Rate
Period-1
Period- 2
Abs Coefft
Heating Rate
Heating Rate
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CALIPSO Aerosol Depth Ramanathan et al, Nature,
2007
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Trends in Drought Severity Index 1900 to 2002

• Global decrease in soil moisture content
• Long term trends
• Sahel drought
• Indian monsoon
• Northern China
• Australia
• Amazon
• SW N. America

IPCC 2007
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Fig. 12
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How are the following regulated? Super
saturation 3-D structure of
Clouds Size spectrum of Clouds
Large Scale Convergence
Entrainment
Moisture flux
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The Pacific Dust Experiment (PACDEX)Chief
Scientists Stith and Ramanathan
Example of dust plume event crossing the Pacific
Ocean in six days during April 1998 from Husar
et al. (2001)
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PACDEX Science Team (to-date)
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Pacific Dust Experiment NCAR-GULF V
Following the Dust-Soot Plume Across the Pacific
Ocean
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50N,140W
35N,140W
30N,145W
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How Close are we to simulating optical properties
of low Clouds?
Model Simulation with observationally constrained
LWC thermodynamic fields cloud fraction
Uncertainties Sea Salt fluxes Organics
Cloud Thickness vertical stacking
Ref Feng and Ramanathan 2007
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How Close are we to simulating optical properties
of low Clouds?
Model Simulation with observationally constrained
LWC thermodynamic fields cloud fraction
Uncertainties Sea Salt fluxes Organics
Cloud Thickness vertical stacking
Ref Feng and Ramanathan 2007
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Ramanathan et al, 1995
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Why is the Planets Albedo 29 ? Was it always
29 ? Regulating Factors Chemistry physics
(Aerosol-cloud-precipitaion) Biotic processes (
CCN IFN) Atmospheric Dynamics (
Cloud Morphology spatial structure)
What is the role of feedbacks between Chemistry,
Biology and Dynamics?