April 11, 2008

Hurricanes (Continued)

o While variations in the total number of hurricanes in the Atlantic Ocean is interesting, keep in mind that most people only remember the ones that cause death and destruction on the coast. Many Atlantic hurricanes stay out at sea or are relatively weak when they make landfall. Those few hurricanes that reach category 4 and 5, only remain at that strength for short periods of time, which on average is less than 24 hours. The chance that one of these monsters will hit the U.S. mainland as a category 4 or 5 storm is relatively low. However, these strong landfalling hurricanes are the ones that cause the most deaths and destruction. These are that storms that coastal residents need to be prepared to deal with.

§ Show link to a web page that shows the location of all major landfalling hurricanes to hit the United States since 1899. Note that the average over the period from 1899 through 2005 is less than one per year. However, in 2004 there were 3, followed by 4 more in 2005. There were no major hurricanes to strike the US coastline in 2006 and 2007.

n Cost of US hurricanes

o Generally speaking, in the United States, hurricanes cause the most dollar damage of any category of severe weather, but relatively few deaths.

o Before Katrina happened, I would present statistics about the effects of hurricanes on the United States which clearly showed the following trends:

§ The damage costs due to hurricanes in the US (in terms of dollars) was increasing with time from the early 1900s onward. This trend included factoring in the rate of inflation.

Ø The increasing trend in property damage results from the fact that much building is occurring along America's coastlines. People want to live on the coast and vacation on the coast. As competition for this property increases, the value of the property increases. High priced homes and resorts are built in hurricane prone areas. This includes re-building in areas damaged by previous hurricanes.

§ Loss of life associated with hurricanes was decreasing from the early 1900s until Katrina hit in 2005.

Ø The decreasing loss of life results from two factors. In the early part of the century before satellite imagery and sophisticated forecasting methods, people had little warning of an approaching hurricane, and many were killed. In fact the Galveston, TX hurricane of 1900 still ranks as the most deadly in U.S. history with from 8 to 12 thousand deaths. In modern times, people are warned of an approaching storm and either evacuate or make necessary preparations. It seemed that public awareness and preparation had lowered death counts (even though more and more people now live on the coast) until Katrina.

n Why was Katrina so deadly?

o Katrina forces us to reconsider the long-held belief that hurricanes will not cause many deaths in the United States because we have such a great hurricane monitoring system and no storm will catch anyone by surprise. Sure property damage was high (Katrina has surpassed Andrew as the most expensive hurricane ever), but we have come to expect that. We can deal with property damage, but we should not have to except the number of human deaths and injuries that resulted from Katrina.

o The question here is: Even with the ample warning provided by the National Hurricane Center, why did so many people die as a result of Katrina? Last count is over 1300 confirmed deaths. This is the most deaths related to a single hurricane since 1928.

§ See figure 11.25 to see how well Katrina’s path was forecasted.

o Undoubtedly the vulnerability of the New Orleans area to levee failure and flooding was a strong contributing factor and had Katrina hit somewhere else there would have been less loss of life.

o The one course of action that will always work to save lives is for people to evacuate the area before the storm hits. Unfortunately with Katrina many residents remained even though they were warned in ample time to leave.

§ We can argue about whether this was the government’s fault or whether the responsibility should be placed on the individuals who made personal decisions to not evacuate.

§ And no doubt, federal and local government screwed up in their response to the disaster making it worse than it might have been.

§ But again, the only sure way to save lives is for people to evacuate before the storm hits. Hopefully, Katrina will act as a wake up call for those living in hurricane-prone areas. Don’t take chances or at least understand the risk that you and your family take by not heeding warnings.

§ A Katrina-type disaster was foreseen by many people. In fact a New Orleans newspaper published an article in 2001 about a devastating scenario eerily close to what actually happened, including levee failure, with many residents becoming trapped. Others just warned about how the people living in hurricane-prone areas seemed unaware of the potential damage that can occur when major hurricanes make landfall and would not take appropriate action.

Ø People living in hurricane prone areas need to understand the devastation that hurricanes can cause, keep informed on hurricane activity in their area, and be prepared to make intelligent decisions. People in New Orleans had the additional responsibility to understand the vulnerability of their city to the possibility of levee breaks whenever a major storm is near.

Radiation (Chapter 2, pg. 31 forward)

n Radiation is the transfer of energy by electromagnetic wave motion. Electromagnetic energy emitted (or given off) by one object is delivered to another object when it is absorbed by that object.

n Radiation is the most important energy transport process because it is able to travel through empty space (a vacuum), while the other two basic energy transport processes, conduction and convection, both require that matter be present to accomplish the energy transport.

n We will now go through the supplemental reading material to help describe what is meant by an electromagnetic wave, how are different types of radiation distinguished, and several fundamental laws of radiation emission. I believe that the material presented in the supplemental reading will be easier to understand than the material in the textbook.

o The supplemental reading page for electromagnetic radiation is available under the reading link on these class web pages. I strongly suggest that you read over this material before coming to class. It may also be helpful to print the pages so that you have them in front of you when we discuss this material.

n Quick Summary

o Review figure showing electromagnetic spectrum (linked on lecture notes page)

o All objects in the universe emit (or give off) radiation energy. The amount and type of radiation emitted depends strongly on the temperature of the object.

§ The higher the temperature, the more total energy radiated

§ The higher the temperature, the shorter the wavelength of the peak radiation energy emission.

Ø Therefore, the hot sun emits much more radiation energy than the cooler Earth and its peak emission is at a much shorter wavelength than the Earth.

o See figure 2.9. Peak emission for the Sun falls into the visible radiation category, while peak emission for the Earth (and most objects on the Earth) is infrared radiation, which we cannot see with our eyes.

n Photons

o At a very basic level, radiation energy is emitted photon by photon. Billions upon billions upon billions … of photons. We have seen that different types of radiation can be described by the wavelength of its electric and magnetic fields (shorter wavelengths are said to carry more energy). Alternatively, different types of radiation can be described by the energy carried by a single photon. Keep in mind that there exists a continuous spectrum of photon energies in the universe.

§ Because only a small fraction of all the radiation energy emitted from the Sun is in the form of ultraviolet radiation (figure 2.8), we can say that the Sun emits many more visible photons than ultraviolet photons (equating to more visible radiation energy than ultraviolet); however, each ultraviolet photon carries more energy than each visible photon.

o At the very basic level, radiation energy is absorbed photon by photon as well. With respect to human well-being, an important issue here is what happens to a living cell when it absorbs a photon.

§ An ultraviolet photon has enough energy to damage or destroy the DNA in a living cell when it is absorbed.

§ A visible photon does not contain enough energy to damage the cell when it is absorbed.

§ Thus the absorption of many visible photons does not cause a problem, but the absorption of a single ultraviolet photon can cause problems. This is why we must protect ourselves from exposure to ultraviolet radiation (photons).