exceptweath - Exceptional Weather I EENS 204 Tulane...

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This document last updated on 16-Mar-2004 EENS 204 Natural Disasters Tulane University Prof. Stephen A. Nelson Exceptional Weather (Part I) Exceptional Weather Here we cover weather related phenomenon, including severe thunderstorms, tornadoes, tropical cyclonic storms (hurricanes, typhoons, and cyclones), nor'easters, drought, and the causes and effects of El Niño. We have already discussed the factors involved in the circulation of the atmosphere and oceans. Knowledge of the general atmospheric circulation patterns, the Coriolis effect, and circulation around high and low atmospheric pressure areas from the previous lecture is essential for understanding the material in this section. Water and Heat Water has one of the highest heat capacities of all known substances. This means that it takes a lot of heat to raise the temperature of water by just one degree. Water thus absorbs a tremendous amount of heat from solar radiation, and furthermore, because solar radiation can penetrate water easily, large amounts of solar energy are stored in the world's oceans. Further energy is absorbed by water vapor as the latent heat of vaporization, which is the heat required to evaporate water or change it from a liquid to a vapor. This latent heat of vaporization is given up to the atmosphere when water condenses to form liquid water as rain. If the rain changes to a solid in the form of snow or ice, it also releases a quantity of heat known as the latent heat of fusion. Thus, both liquid water and water vapor are important in absorbing heat from solar radiation and transporting and redistributing this heat around the planet. Exceptional Weather I 3/16/2004 Page 1 of 10
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Air Masses Due to general atmospheric circulation patterns, air masses containing differing amounts of heat and moisture move into and across North America. Polar air masses, containing little moisture and low temperatures move downward from the poles. Air masses that form over water are generally moist, and those that form over the tropical oceans are both moist and warm. Because of the Coriolis effect due to the Earth's rotation, air masses generally move across North America from west to east. But, because of the differences in moisture and heat, the collision of these air masses can cause instability in the atmosphere. Fronts and Mid-latitude Cyclones Different air masses with different temperatures and moisture content, in general, do not mix when they run into each other, but instead are separated from each other along boundaries called fronts. When cold air moving down from the poles encounters warm moist air moving up from the Gulf of Mexico, Pacific Ocean, or Atlantic Ocean, a cold front develops and the warm moist air rises above the cold front. This rising moist air cools as it rises causing the condensation of water vapor to form rain or snow. Note that the cold air masses tend to circulate around a low pressure center in a counterclockwise fashion in the northern hemisphere. Such circulation
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This note was uploaded on 11/20/2010 for the course LIR 30 taught by Professor Thornley,k during the Spring '08 term at Santa Rosa.

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exceptweath - Exceptional Weather I EENS 204 Tulane...

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