tropical cyclones (i.e. hurricanes) aos 100 nick bassill april 28 th 2009
DESCRIPTION
An Extratropical Cyclone Different AirmassesTRANSCRIPT
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Tropical Cyclones(i.e. Hurricanes)
AOS 100Nick Bassill
April 28th 2009
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A Review of Extratropical Cyclones
• Recall that extratropical cyclones:- Frequently form in the mid-latitudes- Develop from pre-existing horizontal temperature gradients- Have fronts- Are not very symmetric- Have sizes up to 1000 or more kilometers in any direction
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An Extratropical
Cyclone
Different Airmasses
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An Extratropical
Cyclone
Different AirmassesFronts (temperature gradients)
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An Extratropical
Cyclone
Different AirmassesFrontsAsymmetric
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An Extratropical
Cyclone
Different AirmassesFrontsAsymmetricVery Large
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An Extratropical
Cyclone
Different AirmassesFrontsAsymmetricVery LargeMid-latitudes
~ 30º N
~ 50º N
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Then What Are Tropical Cyclones?• In many ways, tropical cyclones have the opposite
characteristics of extratropical cyclones:- They mostly form between 30º N and 30º S- They develop in areas without a horizontal temperature gradient- They do not have fronts- They are quite symmetric- They typically can only strengthen when over warm water, and weaken over land
• However, like extratropical cyclones, tropical cyclones are also areas of low pressure
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Hurricane Isabel - 2003
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The Storm Center, or “Eye”
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How Do Tropical Cyclones Develop?
• First, tropical cyclones require warm water (typically greater than 80º F)
• The environment must have little vertical wind shear (change in wind speed or direction with height)
• Some initial disturbance, such as a complex of thunderstorms, which may slowly develop
• If these conditions persist for several days, a tropical cyclone may form
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Common Development Regions Are In Orange
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How Do Tropical Cyclones Strengthen?
• Most simplistically, tropical cyclones strengthen and maintain themselves through latent heat release
• Large quantities of latent heat release warm the air, causing it to be less dense than surrounding air
• The ideal gas law tells us that the pressure should then decrease
• The storms must be over a warm ocean surface to supply enough moisture
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A 3-D Look
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Thunderstorms
Air near the center is heated much more than air at a distance
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Air converges at the surface
Air diverges at the top
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Comparison of extratropical vs. tropical pressure
distributions
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Stages Of Hurricane Development• So far, only Hurricanes have been shown• However, when these disturbances first
appear, they are called “Tropical Depressions” and do not receive a name
• Once the disturbance is sufficiently strong, it is deemed a “Tropical Storm” and given a name, which occurs when the surface winds become stronger than 39 mph
• After further strengthening, the system is upgraded to a “Hurricane” after the surface winds strengthen to greater than 74 mph
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From: http://www.pennwellblogs.com/tropics_watch/wp-content/uploads/2008/10/saffir-simpson.gif
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Storm Surge Explained
• As the winds converge toward the storm center, they help “pile up” ocean water
• Also, the decreased surface pressure raises the sea level slightly
• Strong waves also can increase the water height
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What Causes The Most Damage?
• Many different aspects of a hurricane can cause damage:
- Very strong winds can damage structures- Heavy rainfall can cause flooding- Storm surge associated with rising ocean
waters can inundate low-lying areas- Occasionally, lightning strikes and/or
tornados can also cause damage
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The Answer Is: Storm Surge• Generally storm surge causes the most
damage and deaths, particularly in strong hurricanes
Damage from Hurricane Ivan
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Hurricane Katrina (2005)
• At its most intense, Hurricane Katrina was the 6th strongest on record for the Atlantic Ocean
• Its lowest pressure was 902 mb, and it’s strongest sustained winds were 175 mph
• Luckily, Katrina weakened slightly before landfall• However, approximately 2500 dead and missing
people are attributed to Katrina• Damages of roughly $100 billion were caused by
Katrina
To learn more, visit http://en.wikipedia.org/wiki/Hurricane_Katrina
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Hurricane Katrina’s Track
http://en.wikipedia.org/wiki/Hurricane_Katrina
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A Story: Even “Smart” People Make Mistakes
• Myself, my advisor, and a fellow graduate student wanted to experience a hurricane, so we (un)luckily chose Katrina to be our first
• http://aurora.aos.wisc.edu/~bassill/katrina.htmlThis is the point we left Madison
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A Map
Slidell
Pascagoula
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Actual hotel
eviction notice from
Slidell
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Next Stop: Pascagoula
Specifically
About Two Miles
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