ByGreg 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*

*Source, NOAA, October 26, 1998

Narrow Eye

Central Dense Overcast

Healthy Outflow

ReferencesAhrens, 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, 1139-1152.

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.