1. AOS 100: Weather and Climate
Instructor: Nick Bassill
Class TA: Courtney Obergfell

2. Miscellaneous Extra Credit Offer Requirements: - ~4 pages
- pick a topic that interests you, and me
- include a few references
- relate it back to lecture somehow
- due no later than December 15th! (the last day of class)

3. 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

4. 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

5. 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 August-October
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

6. 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

7. A 3-D Look

8. Air near the center is heated much more than air at a distance
Thunderstorms

9. Air diverges at the top
Air converges at the surface

11. Comparison of extratropical vs. tropical pressure distributions

12. 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

14. From: http://www. pennwellblogs

15. 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

16. 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

17. The Answer Is: Storm Surge
Generally storm surge causes the most damage and deaths, particularly in strong hurricanes
Damage from Hurricane Ivan

18. 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?