Transcript Tropical Cyclones Continued

AOS 100: Weather and
Climate
Instructor: Nick Bassill
Class TA: Courtney Obergfell
Miscellaneous
• Extra Credit Offer Requirements:
- ~4 pages
- pick a topic that interests you, and e-mail me
- include a few references
- relate it back to lecture somehow
- due no later than December 15th! (the last day
of class)
Review of November 19th: Thunderstorms
and Tropical Cyclones
• Squall lines are long linear bands of
thunderstorms known for causing strong wind
damage
• They are mostly associated with speed shear
• The wind damage is caused by dry air entering
the storm, which cools rapidly as rain evaporates
into it
• When it cools, it sinks quickly and hits the
ground and spreads out, causing strong winds
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
- They generally move from east to west, rather
than west to east
• However, like extratropical cyclones, tropical
cyclones are also areas of low pressure
Tropical Cyclone Review
• In many ways, tropical cyclones are the opposite
of extratropical cyclones, with the exception that
they are both areas of low pressure
• In the Atlantic, most develop from AugustOctober
• In order for tropical cyclones to develop, they
require:
- Warm water (~80º F or more)
- Little wind shear
- A cluster of thunderstorms persisting for several
days
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
A 3-D Look
Air near the center is heated much
more than air at a distance
Thunderstorms
Air diverges at the top
Air converges at the surface
Comparison of
extratropical
vs. tropical
pressure
distributions
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
From: http://www.pennwellblogs.com/tropics_watch/wp-content/uploads/2008/10/saffir-simpson.gif
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
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
The Answer Is: Storm Surge
• Generally storm surge causes the most
damage and deaths, particularly in strong
hurricanes
Damage from Hurricane Ivan
Exam 3 Review
• The only general topics we’ve talked about are
Thunderstorms and Tropical Cyclones
• For thunderstorms, know:
- the different types, and how you distinguish them
- i.e. what characteristics make something a
supercell vs. a squall line?
- what is Doppler radar, what is it used for?
- what is the LCL, LFC, and CAPE? (you DO NOT
need to know how to find them on a Skew-T)
• Tropical Cyclones:
– How are they different from extratropical cyclones?
– How do they form/intensify?