Transcript The Physicist as Consultant to the Real world

Hurricanes
Smoking Guns of Climate Change or
random occurrences?
Climate Change and Chaotic Dynamics:
Hurricane Example
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Naive expectation is that steadily rising sea
surface temperatures (SST) should produce
increasingly strong hurricanes
After 2005 Katrina, Rita and Wilma there was a
rash of papers on how increasing hurricane
strength was now a manifestation of global
climate change
Needs reality check
Atlantic Hurricane Formation
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Low pressure centers form over Sahara desert
and may get amplified as they cross open ocean
Amplification depends critically on SST and
available moisture in the atmosphere
Must also have favorable wind conditions (light
winds aloft) and weak wind shear
It is not just SST that drives hurricanes
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Hurricane Frequency
Increasing?
This is difficult to establish with a high
degree of statistical confidence;
Incompleteness is an important issue
Counting is always noisy
Yellow = raw data
Red = corrected
RADAR in the 1950s
Landfall Frequency vs Decade
landfall
total
proportion
1900
27
40
0.675
1910
29
37
0.78378378
1920
25
42
0.5952381
1930
36
47
0.76595745
1940
34
50
0.68
1950
34
69
0.49275362
1960
26
61
0.42622951
1970
23
49
0.46938776
1980
21
52
0.40384615
1990
24
64
0.375
2000
40
74
0.54054054
585
1900-1949
151
216
0.69907407
1950-2009
168
369
0.45528455
Using landfall frequency as a proxy
• Shows that significant incompleteness (25-50%)
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exists in the pre-radar era
There is no reason to the frequency of Atlantic
basin hurricanes to have any systematic in their
decade averaged land fall frequency.
This makes it pretty clear that hurricanes are not
increasing in frequency in response to slow rise
of SST.
Decadal variations are much larger than any
systematically increasing baseline
Hurricane Energetics
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Total amount of energy release as latent heat
(condensation of water droplets)
The amount of kinetic energy needed to
maintain the hurricane wind field (and overall
movement)
Latent Heat
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Hurricane produces 2 cm per day averaged over
a radius of 600 km
Volume of rain = 10^16 cm^3/day = 10^16
grams per day
Latent heat of vaporization is 2475 KJ/Kg (at
typical hurricane temperature)
Gives 2.5 x 10^16 Joules/per day or 3 x 10^14
Watts (300 TW !!!)
Kinetic Energy
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KE generated = amount dissipated due to
friction
Dissipation Rate per unit area = air density *
drag coefficient * velocity^3
Ro is some characteristic outer radius which is largely unknown for
pre-satellite hurricanes.
Energetics
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Suitable averages over wind velocities (90 mph
over a scale of 60 km) yields 1.5 TW of
“kinetic” power
The total energy output of the world in all
forms is 14 TW
14 is bigger than 1.5 but not bigger than 300
Which energy scale is most relevant for
hurricane formation and evolution? If 300 then
humans are doing squat.
What does Data Tell us?
• A Central Pressure
• A hurricane wind radius (quite
variable)
• A duration
• A location (time dependent)
• An evolutionary timescale (spin
up times)
• Category X at landfall
Decadal Location Analysis – only 1 region
shows upward systematic trend in counts
per decade per cell
Central Pressure Evolution
But strongest storms may be
increasing
Note that 2009 was weakest Atlantic Basic Hurricane Season
over the last 20 years; 2005 was the strongest
Strong Decadal Location Variability
on spatial scale of 3x3 degrees
Spin up Times getting faster
This is a Physical Signature associated with change in convection
rates but data has to support this conjecture.