CHAPTER 5 Focus Points
5.1 Thunderstorms
Spatial and temporal scales: Microscale atmospheric systems last hours, and synoptic and global atmospheric systems last weeks to months.
Air masses: Warm and humid mT air masses are essential for thunderstorm development.
Thunderstorm geography: Thunderstorms are most frequent in the tropics over land.
Thunderstorm types: There are three types of thunderstorms: single-
5.2 Thunderstorm Hazards: Lightning and Tornadoes
Lightning and thunder: Lightning is a discharge of electricity within a thunderstorm. Thunder is created as air is heated by lightning and rapidly expands.
Tornadoes: Tornadoes form in thunderstorms, hurricanes, and cold fronts. The United States has the most frequent and strongest tornadoes in the world.
5.3 Nature’s Deadliest Storms: Hurricanes
Hurricane structure: Hurricanes consist of a calm eye, an eyewall of heavy wind and rain, and rain bands.
Hurricane strength: Hurricanes must have warm seawater to persist. They derive their strength from the latent heat positive feedback.
Stages of growth: Hurricanes go through a series of stages of formation, from tropical wave, to tropical disturbance, to tropical depression, to tropical storm, to tropical cyclone.
Hurricane geography: Worldwide, hurricanes are restricted to tropical oceans. They do not occur within about 5° latitude of the equator due to the lack of Coriolis force there.
Hurricane hazards: The coastal storm surge is the most dangerous aspect of a hurricane, particularly in the Indian Ocean.
5.4 Midlatitude Cyclones
Midlatitude cyclone effects: Midlatitude cyclones bring storms to midlatitude regions, such as the United States and Canada, from fall through spring.
Warm and cold fronts: Most midlatitude cyclones are composed of warm fronts that bring steady precipitation and cold fronts that bring bursts of short-
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Stages of development: A midlatitude cyclone undergoes a sequence of growth, maturation, and dissipation over the span of days to weeks.
5.5 El Niño’s Wide Reach
El Niño impacts: El Niño rearranges moisture and weather patterns for many regions, causing drought and flooding for many parts of the world. El Niño brings fewer hurricanes for the Atlantic Ocean, and it often weakens the Asian monsoon.
La Niña: La Niña often follows El Niño and creates “enhanced normal” meteorological conditions for affected areas.
5.6 Geographic Perspectives: Are Atlantic Hurricanes a Growing Threat?
U.S. cities at risk: Except for New Orleans, Miami is the largest metropolitan area most at risk for a hurricane disaster.
Long-