Lecture Ch. 12
The Atmospheric “Heat Engine”
• Atmospheric heat engine
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Latitudinal and meridional heat transfer
Walker circulation and Aus-Asia monsoons
Efficiency, irreversibility, entropy
Hydrological cycle
• Current research
– Aerosols, precipitation, and evaporation
Curry and Webster, Ch. 12
For Tuesday: Read Ch. 13
For Nov. 30: Review Past Homework, Quizzes, Reading, Midterm
Latitudinal Heating Distribution
• Net heating at equator
• Net cooling at poles
Heating and Circulation
• Fluid motion from vertical density gradient
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Meridional Heat Transfer
• Equator-to-pole heat transport
Zonal Heat Transfer
• Walker circulation
• Asian-Australian monsoon
Atmospheric Heat Engine
2
Atmospheric Entropy
• Difference between energy and entropy flux
• Irreversible processes
Atmospheric Entropy
• Internal production of entropy by Earth
Hydrological Cycle
• Definition
• Residence times
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Current Research: Radiation
“These aerosol effects
can lead to a weaker
hydrological cycle,
which connects
directly to the
availability and
quality of fresh
water...”
• Large surface cooling: -20 W m-2
– Reduces evaporation, short-circuiting
precipitation
Ramanathan et al., 2001
Current Research: Cloud Drops
Current Research: Global Models
• Aerosol
impacts on
rain are not
local
• Additional particles also
reduce droplet size
– Slowing growth to
precipitation-size droplets
Change in JJA mean
precipitation (mm day1) between the 6-year
perturbation and the 12year control.
Ramanathan et al., 2001
Erlick, Ramaswamy, and Russell, 2005
Asian Mixed BC
U.S. Combustion
(clear)
“Many of these particles
contain carbonaceous
components from mineral
dust and combustion
emissions in Africa, Asia,
and North America and
reveal reaction rates that
are three times slower
than those typically used
in climate models...”
“…aerosols counteract
warming by an uncertain,
but potentially large,
amount…Strong aerosol
cooling would imply that
future global warming may
proceed at or even above the
upper extreme of the range
projected by the IPCC.”
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