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 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

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

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?