Transcript Document

By
Greg Machos
December 4, 2003
Agenda
Introduction
Hurricane Development
 Essential Ingredients
 Theories on Tropical Cyclogenesis
Category Five Hurricanes--Optimum Intensity
 Requirements
 What Happens Inside Category Five Hurricanes
Category Five Hurricanes--How They Lose Their Punch
 Maximum Potential Intensity--Emanuel
 Analysis of MPI--Persing and Montgomery
 Causes of Weakening
Conclusion
Introduction
Hurricanes--A Combination of Beauty and Fury
 Provide A Breathtaking View From Space.
 Carry A Devastating Punch At The Surface.
Classifying Hurricanes--The Saffir-Simpson Scale
 Categorizes Hurricanes In Terms of Wind And Pressure.
 Ranges From Category One To Category Five Intensity.
Category Five Hurricanes--A Rare Breed
 Account For Less Than 5% Of All Atlantic Hurricanes.
 Also Represent Hurricanes At Maximum Efficiency.
 Can’t Sustain Such High Intensity For Long.
 Due To Changes In Its Environment and Within Itself.
Saffir-Simpson Scale*
Category
Sustained
Winds (ms-1)
Minimum
Central
Pressure (mb)
Storm Surge
(meters)
Category One Hurricanes
33 to 42 ms-1
>=980 mb
1.5 meters
Category Two Hurricanes
43 to 49 ms-1
965-979 mb
2.0-2.5 m
Category Three Hurricanes
50 to 58 ms-1
945-964 mb
2.5-4.0 m
Category Four Hurricanes
59 to 69 ms-1
920-944 mb
4.0-5.5 m
Category Five Hurricanes
>69 ms-1
<920 mb
>5.5 meters
*Source: Ahrens, Meteorology Today, 2003
Long Lasting Category Five Storms*
Storm Name
Year
Duration (hours)
Hurricane Dog
1950
60 hours
Hurricane David
1979
42 hours
Hurricane Mitch
1998
42 hours
Hurricane Isabel
2003
36 hours
Unamed Hurricane
1947
30 hours
Hurricane Camille
1969
30 hours
*Source: The Weather Channel, September 2003
Hurricane Development
Essential Ingredients
 Sea Surface Temperatures at or above 26.5 0C.
 Light Winds Aloft.
 Plenty of moist air from the surface upward.
 Rotation or spin--Forcing surface winds to converge.
Theories--Tropical Cyclogenesis
 Organized Convection Theory.
 Heat Engine Theory--Based on Carnot Cycle.
 Combination of both theories.
 Analysis--Heat Engine Theory Makes More Sense.
Organized Convection Theory*
Thunderstorms must be
organized.
Cold air must be present
aloft for instability.
Latent heat must be
released at upper levels.
Latent heat at upper levels
results in high pressure.
High pressure creates good
outflow or exhaust for the
storm.
*Source, Ahrens, Meteorology Today, 2003
Heat Engine Theory*
Based on Carnot Cycle.
Transfers heat from warm
ocean surface (warm
reservoir).
To the upper levels of the
troposphere (cold reservoir).
Transfer results from work
done by small swirling air
currents.
Pressure gradient results
from temperature difference
between the air aloft in the
eye, and air aloft at periphery.
*Source, Stull, Meteorology for Scientists and Engineers, 2000
Category Five Hurricanes--Optimum
Meteorological Requirements
 Sustained Winds Exceeding 69 ms-1.
 Minimum Central Pressure Below 920 mb or 0.91 atm.
Thermodynamic Requirements--Goldilocks Principle
 Conditions are “just right.”
 Sea Surface Temperatures Above 28 0C.
 Adequately Moist Air at altitudes between 1.5 to 5 km.
 Little or no wind shear at upper levels of atmosphere.
Rapid Intensification
 Another characteristic of Category Five Storms.
 Process takes hurricane from Cat 1 or 2 to Cat 4 or 5.
 Occurs often in warm eddies, or deep, thick warm water.
Inside Category Five Hurricanes
Narrow and Well Defined Eye
 Eye clear because of warm, sinking air in center.
 Eye narrows to conserve momentum.
Classic Buzz Saw Shape
 Combination of healthy outflow and organized CDO.
 Outflow acts as exhaust for heat and moisture.
 Organized Central Dense Overcast--Thunderstorms.
 Essential for highly efficient heat engine to keep going.
Eyewall Replacement
 Occurs in most major hurricanes.
 Result of Rapid Intensification.
 Can cause Concentric Eyewalls.
A Look At A Category Five Hurricane*
Narrow Eye
Central Dense Overcast
Healthy Outflow
*Source, NOAA, October 26, 1998
References
Ahrens, Donald C., 2003: Meteorology today: An introduction to weather, climate, and the environment.
Thomson Learning, Inc.
Ban, Ray. 1992: Danger’s Edge. [Video] The Weather Channel.
Bister, M., and K.A. Emanuel, 1998: Dissipative heating and hurricane intensity. Meteorol. Atmos. Phys.,
65, 233-240.
Elsner, J.B., and A.B. Kara., 1999: Hurricanes of the North Atlantic: Climate and society. Oxford University
Press.
Emanuel, Kerry A., 2000: A statistical analysis of tropical cyclone intensity. Mon. Wea. Rev., 128, 11391152.
Emanuel, Kerry A., 1999: Thermodynamic control of hurricane intensity. Nature, 401, 665-669.
Emanuel, Kerry A., 1988: The maximum intensity of hurricanes. J. Atmos. Sci., 45, 1143-1155.
Hoversten, Paul., 29 September 2000: “Scientists study why hurricanes intensify.” USA Today. [Online]
http://www.usatoday.com/weather/huricane/science/whgascan.htm
Iacovelli, Debi., 1999: Concentric eyewalls of hurricanes: An interview with Dr. Hugh E. Willoughby. NOAA
Mariner’s Weather Log, 43, 4-9.
Persing, J., and M.T. Montgomery, 2002: Hurricane superintensity. J. Atmos. Sci., 205, 5-50.
Remer, Fred., 2003: “Second Law of Thermodynamics.” [MS PowerPoint] University of North Dakota.
Stull, Roland B., 2000: Meteorology for scientists and engineers: Second edition. Thomson Learning, Inc.
Stewart, Stacy. 18 September 2003: Internet e-mail interview.
Wallace, J.M. and P.V. Hobbs. 1977: Atmospheric science: An introductory survey. Academic Press.
Willoughby, Hugh. 13 November 2003: Internet e-mail interview.
Questions
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Hope you enjoyed the presentation.