Coastal Processes, Hazards, and Society

Learning Check Point


Learning Check Point

Quick Review

Watch the following two videos for review and answer the Learning Check Point questions to be sure you have understood the material provided.

The following video provides an animation of the 2005 hurricane season, with an excellent review of the conditions required for active hurricane formation.

Video: Hurricanes Explained: How 2005 Was the Perfect Storm (4:56)

Hurricanes Explained: How 2005 Was the Perfect Storm
Credit: flingjore
Click for transcript of Hurricanes Explained: How 2005 Was the Perfect Storm video.
PRESENTER: 27 Storms-- Arlene to Zeta. Let's examine what made conditions so favorable for Atlantic storm formation in 2005. We begin with the ocean. These are sea surface temperatures for the 2005 hurricane season, changing through time as the calendar advances. Warm water powers hurricanes. Orange and yellow areas show zones with water warmer than 82 degrees, the threshold favorable for hurricane development. Let's start the season again, this time adding clouds back into the picture. Atlantic Basin hurricanes typically formed between June and November. Hurricanes often start as atmospheric disturbances off the coast of West Africa. Once out into the warm summer waters of the mid-Atlantic, some ripples begin to rotate and, feeding off of warm water, strengthen into hurricanes. Hurricanes require warm water to heat air above the ocean, causing a drop in air pressure. Lower air pressure sucks more water vapor into the storm, causing storms to strengthen. As hurricanes pass over warm water, they leave trails of relatively cooler water, so-called cold water trails. Numbers displayed over storm tracks indicate hurricane category changes. Strong shearing winds in the troposphere can disrupt this process, weakening young storms. But measurements indicate that there was very little shearing wind activity in 2005 to impede storm formation. Hurricanes are rare phenomena. Only about 80 or 90 appear worldwide every year. Storms stalked the Atlantic Ocean and eastern seaboard from June until early winter in 2005, and the record books are groaning under the strain of such a busy year. Consider this list of superlatives. An average year produces roughly 10 storms. 27 named storms formed in 2005. An average year produces six hurricanes. 15 formed in 2005. An average year produces two major hurricanes. Seven formed in 2005. On average, one category 5 hurricane forms every three years. In 2005, there were three-- Katrina, Rita, and Wilma. Wilma was the most intense Atlantic hurricane ever recorded, Katrina fourth, Rita sixth. But Katrina was the most destructive hurricane ever to hit the United States. The total losses from storms in 2005 include more than 1,200 lives and potentially more than $100 billion. This visualization shows some of the actual data that NASA and NOA satellites measured this season, data used to predict the paths and intensities of hurricanes. Satellite data play a vital role in helping us understand the land, ocean, and atmosphere systems that have such dramatic effects on our lives.

This NASA video explains the mechanism of tropical cyclone formation in terms of heat transfer.

Video: Hurricane Heat Engine (2:05)

The Hurricane Heat Engine
Credit: NASA Video
Click for a transcript of The Hurricane Heat Engine video.
PRESENTER: This just brings everything together I just explained to you, going back to the cartoon, which is really nice. You see all these little sparklies zipping around this cloud? That's our attempt to illustrate latent heat. This is our attempt to illustrate that when water vapor condenses into liquid, all this heat energy gets released, OK? So basically, we have the condensation, which warms up the air inside these giant chimney clouds. The air rises like it's going up on a hot air balloon. And then as the air hits the top of the tropopause, it must spread out in all directions. And as it does so, some of the air comes back down in the center, right back down-- the eye of the storm. And when that air comes down, something important happens to it. It compresses and it warms. Much like you take a bicycle pump, and you pump it up really hard, and you feel the metal cylinder. It gets hot. That's from compressing air. And it's that warm air that builds inside the eye that gives the hurricane its real energy because this warm air is being trapped by the rotating winds of the vortex. It can't escape. And when the column of air gets warmed up, the density of this air is less than its surroundings. The molecules are exerting less pressure on the surface, and that's why a column of warm air means that the pressure drops right above the ocean surface. The air rushes in to fill the low-pressure void, and lo and behold, a hurricane is born. You see, these storms become kind of self-sustaining after a while. The inflow creates more rising motion, which creates sinking in the eye, which warms up the interior, which brings in more air. It's self-sustaining.

Take a few minutes to answer the questions below.