Folie 1

1
We are going to show that hurricanes are (in good
approximation) a natural realization of the
Carnot cycle.
rare South Atlantic tropical cyclone viewed
from the International Space Station on March 26,
2004.
2
Some basics about tropical cyclones
for details read

• tropical cyclones a storm system with a closed
  circulation (cyclonic)
• around a center of low pressure that
  originates over tropical oceans
• and is driven principally by heat transfer
  from the ocean

counterclockwise circulation in the Northern
Hemisphere

• Categorization of tropical cyclones maximum
  averaged wind speed

17 m/s or less
tropical depression
18 to 32 m/s
tropical storm
called hurricanes in the western North
Atlantic and eastern North Pacific regions
33 m/s or greater
typhoons in the western North Pacific
severe tropical cyclones elsewhere
3
Structural elements of a tropical cyclone

• Basic flows

origin of circulation is the Coriolis force
Primary circulation
Brief reminder to the Coriolis force
Exact
ac
Coriolis force
4

• Eye, Eyewall and
• Rainbands

Secondary circulation
Very high wind speed due to conservation of
angular momentum
click for animation
5
The hurricane as a Carnot heat engine
see for details
air undergoes isothermal expansion as it flows
toward the lower pressure of the storm center
while in contact with the surface of the ocean
(heat bath _at_ Ts?300K)
A?B
B?C
Adiabatic (very fast) ascent of the air
air flows out at the top of its trajectory and is
incorporated from the extreme low pressure
region into other weather systems via an
isothermal compression (heat bath _at_ T0?200K)
C?D
D?A
air undergoes an adiabatic compression when
loosing altitude fast
6
PV-Diagram of the hurricane Carnot engine
7
Where does the work go which the hurricane
produces from the heat of the ocean
Devastation by hurricane Katrina, City of
Huntington Beach
stationary state
Generated work per time dissipated (friction)

• dissipation

• rate of heat transfer from the ocean to the
  atmosphere

quantifies the thermodynamic disequilibrium
between the ocean and atmosphere
8
We know the textbook efficiency of a Carnot
engine
important difference to textbook Carnot cycle
tropical cyclones
textbook Carnot cycle
work used for turbulent dissipation
work done on environment
transformed back into heat _at_Ts
back into the front end of the Carnot cycle
heat from the ocean
and
Heat from turbulent dissipation
where Eb/a
theoretical upper bound on hurricane wind speed
note T0 ltTs