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Chapter 13, Section 1: Thunderstorms

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Chapter 13, Section 1: Thunderstorms Earth Science Identify the processes that form thunderstorms Compare and contrast different types of thunderstorms Describe the life cycle of a thunderstorm At any given moment, nearly 2000 thunderstorms are in progress around the world Both geography and air mass movements make thunderstorms most common in the southeastern United States For a thunderstorm to form, three conditions must exist A source of moisture For a thunderstorm to form, there must be an abundant source of moisture in the lower levels of the atmosphere Lifting of the air mass For a thunderstorm to form, there must be some mechanism for moisture to condense and release its latent heat This occurs when a warm air mass is lifted into a cooler region of the atmosphere An unstable atmosphere If the surrounding air remains cooler than the rising air mass, the unstable conditions can produce clouds that grow upward This releases more latent heat and allows continued lifting Because the rate of condensation diminishes with height, most cumulonimbus clouds are limited to about 12,000 m Thunderstorms are also limited by duration and size Thunderstorms are often classified according to the mechanism that causes the air mass that formed them to rise There are two main types of thunderstorms Air-mass Frontal When air rises because of unequal heating of Earth’s surface beneath one air mass, the thunderstorm is called an air-mass thunderstorm There are two kinds of air-mass thunderstorms Mountain thunderstorms Occurs when an air mass rises by orographic lifting Sea-breeze thunderstorms Occur because land and water store and release thermal energy differently During the day, the temperature of land increases faster than the temperature of water At night, conditions are reversed Frontal thunderstorms are produced by advancing cold fronts and, more rarely, warm fronts A thunderstorm usually has three stages The cumulus stage In the cumulus stage of a thunderstorm, air starts to rise vertically This creates updrafts The mature stage In the mature stage, updrafts and downdrafts exist side by side in the cumulonimbus cloud The updrafts and downdrafts form a convection cell which produces the surface winds associated with thunderstorms The dissipation stage In a thunderstorm, the cool downdrafts spread in all directions when they reach Earth’s surface This cools the areas from which the storm draws its energy, the updrafts cease, and clouds can no longer form The storm is then in the dissipation stage Lightning is the transfer of electrical charge caused by the rapid rushes of air in a cumulonimbus cloud Friction between the updrafts and downdrafts within a cumulonimbus cloud removes electrons from some of the atoms in the cloud Atoms that lose electrons become positively charged ions, and atoms that receive the extra electrons become negatively charged ions Eventually, the differences in charges break down, and a branched channel of partially charged air, called a stepped leader, is formed between the positive and negative regions When the stepped leader nears the ground, a branched channel of positively charged particles, called the return stroke, rushes upward to meet it and illuminates the connecting channel with about 100 million volts of electricity https://www.youtube.com/watch?v=dukkO7c2eUE A lightning bolt heats the surrounding air to about 30,000C, about five times hotter than the surface of the Sun The thunder you hear is the sound produced as this superheated air rapidly expands and contracts Sound travels slower than light, so that’s why we see lightning before we hear it There are several names given to lightning effects Sheet lightning Heat lightning Spider lightning Ball lightning Blue jets Red sprites. Each year in the United States, lightning causes about 12,000 wildfires and an average of 300 injuries and 58 deaths to humans https://www.youtube.com/watch?v=GQY96bF_Jf0 https://www.youtube.com/watch?v=LIC0_fDp1Xw Reading: pg. 350-354 Homework: pg. 349 (1-8).
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