# Chapter 9 Study Guide, Version 2: Atmospheric Processes and Severe Weather This version follows the textbook section by section. Review each section's summary, key ideas, examples, and questions before moving to the next section. ## Chapter Learning Objectives - **LO:1:** Differentiate the three different ways in which heat is transferred in the atmosphere. - **LO:2:** Discuss how Earth's energy balance and energy exchanges produce climate and weather. - **LO:3:** Compare and contrast the different layers of Earth's atmosphere. - **LO:4:** Explain the different types of severe weather events and discuss the local weather conditions that cause these events. - **LO:5:** Explain how movement of air masses controls the distribution of different severe weather hazards. - **LO:6:** Discuss how humans interact with severe weather. - **LO:7:** Summarize the effects of severe weather events and their linkages to other natural hazards. - **LO:8:** Recognize natural service functions of severe weather. - **LO:9:** Identify how we can minimize the effects of severe weather hazards. ## 9.1 Energy (LO:1) ### Section summary Energy is the ability to do work. Weather involves large energy transfers: a typical thunderstorm does about 10 trillion joules of work, while an average hurricane expends about 100,000 times as much. Solar energy heats Earth's surface, evaporates water, and creates temperature differences that set air masses in motion. ### Energy, work, and power - **Force** is a push or pull that can change an object's motion. It is measured in newtons (N). - **Work** occurs when a force moves an object through a distance in the direction of that force. `Work = force x distance`; it is measured in joules (J). - **Power** is the rate at which work is done, or energy used per unit time. It is measured in watts (W); one watt equals one joule per second. ### Forms of energy and heat - **Potential energy:** Stored energy, such as water held behind a dam. - **Kinetic energy:** Energy of motion, such as falling water. - **Heat energy:** Energy associated with the random motion of atoms and molecules. - **Sensible heat:** Heat that can be measured with a thermometer. - **Latent heat:** Energy absorbed or released when a substance changes phase. Evaporation absorbs latent heat; condensation, freezing, and cloud formation release it. ### Three methods of heat transfer | Method | How heat moves | Importance to weather | |----------------|-----------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------| | **Conduction** | Molecular contact transfers heat from a warmer area to a cooler area. | Limited in the atmosphere because air is a poor conductor; most effective in thin layers touching Earth's surface. | | **Convection** | Mass movement of a fluid, such as rising warm air and sinking cool air, transfers heat. | Drives rising air, cloud growth, thunderstorms, and large-scale atmospheric circulation. | | **Radiation** | Electromagnetic waves transfer energy. | Solar radiation supplies most energy at Earth's surface; Earth emits absorbed energy back at longer wavelengths. | ### Key terms - **Energy:** The ability to do work. - **Work:** Energy expended when a force moves an object through a distance. - **Power:** The rate of doing work or transferring energy. - **Sensible heat:** Heat that can be measured as a temperature change. - **Latent heat:** Heat absorbed or released during a phase change. - **Conduction:** Heat transfer through molecular contact. - **Convection:** Heat transfer by movement of a fluid. - **Radiation:** Energy transfer by electromagnetic waves. ### Section 9.1 review questions 1. How do force, work, and power differ? 2. Compare potential energy, kinetic energy, and heat energy. 3. How do sensible and latent heat differ? 4. Compare conduction, convection, and radiation. Which processes are most important in the atmosphere? ## 9.2 Earth's Energy Balance (LO:2) ### Section summary Earth's energy balance is the general equilibrium between energy arriving from the Sun and energy returned to space. Solar energy powers the hydrologic cycle, ocean circulation, and atmospheric circulation. Incoming solar energy is mostly shortwave radiation; Earth absorbs some, warms, and emits energy at longer infrared wavelengths. ### Electromagnetic energy - **Electromagnetic radiation** travels through space as waves. **Wavelength** is the distance between successive wave crests. - The **electromagnetic spectrum** includes, from shortest to longest wavelengths: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves. - Only a small part of the spectrum is visible light. Incoming solar radiation has shorter wavelengths than outgoing radiation emitted by Earth. ### What happens to solar energy When solar energy reaches Earth, it may be: - **Reflected:** Bounces away from a surface, such as a cloud or the ground. - **Scattered:** Redirected in many directions. - **Transmitted:** Passes through the atmosphere or another material. - **Absorbed:** Taken up by matter, warming it or changing molecular structure. Earth absorbs shortwave solar energy and emits energy at longer wavelengths, mainly as infrared radiation. Greenhouse gases, including carbon dioxide and methane, absorb and re-emit some outgoing energy, helping retain heat in the atmosphere. ### Albedo and heating **Albedo** is the reflectivity of a surface. Lighter surfaces generally have higher albedo and reflect more incoming solar energy; darker surfaces have lower albedo and absorb more energy. For example, the chapter reports that coniferous woodland reflects about 5-15 percent of solar radiation, while grasslands can reflect up to 25 percent. ### Key terms - **Electromagnetic radiation:** Energy transmitted by waves through space or matter. - **Wavelength:** Distance between successive wave crests. - **Energy balance:** General equilibrium between incoming and outgoing energy. - **Albedo:** The proportion of incoming radiation reflected by a surface. - **Infrared radiation:** Longer-wavelength radiation emitted by Earth after it absorbs solar energy. ### Section 9.2 review questions 1. How does Earth's energy balance work? 2. How does wavelength distinguish types of electromagnetic energy? 3. Put gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves in order from shortest to longest wavelength. 4. Why does incoming solar radiation not continually heat Earth without limit? 5. How do surface color and albedo affect heating? ## 9.3 The Atmosphere (LO:3) ### Section summary The atmosphere is a thin envelope of gases, suspended particles, and precipitation around Earth. It produces weather and helps retain heat. Most atmospheric gas molecules are concentrated in the lower atmosphere, and most weather that directly affects people occurs in the troposphere. ### Composition and humidity The atmosphere is mostly nitrogen and oxygen, with smaller amounts of argon, water vapor, carbon dioxide, and other trace substances. Water vapor is essential to cloud formation and atmospheric circulation. - **Humidity** describes the water vapor in the air. - **Relative humidity** is the amount of water vapor present compared with the maximum amount possible at that temperature, expressed as a percentage. - Warm air can contain more water vapor than cold air. Relative humidity can rise as air cools even if the actual amount of water vapor has not changed. - Clouds form when water vapor condenses into tiny liquid droplets or ice crystals. Condensation releases latent heat. ### Layers of the atmosphere The textbook describes four major layers. They are distinguished by how temperature changes with altitude: | Layer | Main characteristics | |------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | **Troposphere** | Lowest layer, about 8-16 km thick. Temperature generally decreases with altitude. Contains most atmospheric water vapor, clouds, and weather. | | **Stratosphere** | Above the tropopause. Temperature rises with altitude in part because ozone absorbs solar radiation; this warming tends to limit vertical mixing from below. | | **Mesosphere** | Above the stratosphere; temperature decreases with altitude. Many meteors burn up in this region. | | **Thermosphere** | Upper layer shown in the chapter; includes auroras and very high temperatures. | The **tropopause** is the upper boundary of the troposphere. It is a relatively stable lid to vertical cloud development, though powerful storm clouds can reach it and spread outward into an anvil shape. ### Section 9.3 review questions 1. What is the atmosphere made of, and what is relative humidity? 2. How do the four atmospheric layers differ? 3. What defines the troposphere, and where does most weather occur? 4. What is the tropopause? 5. How do clouds form, and what happens to latent heat during condensation? ## 9.4 Weather Processes (LO:2, LO:3, and LO:4) ### Section summary Severe weather is associated with atmospheric pressure patterns, vertical stability, the Coriolis effect, jet streams, and interactions between air masses. Uneven solar heating creates temperature and pressure differences. Air movement and rising or sinking motion then shape clouds, storms, and weather hazards. ### Atmospheric pressure and circulation - **Atmospheric pressure** (barometric pressure) is the weight of the air column above a location. It decreases with altitude because less air is overhead. - Cold air is denser than warm air and can exert greater pressure near the surface. Differences in temperature and air movement create horizontal pressure differences. - Air generally flows from high-pressure areas toward low-pressure areas. Surface winds converge toward low-pressure centers, where air tends to rise and clouds can form; winds diverge from high-pressure centers, where air tends to sink and skies are often clearer. - **Convergence** is airflow into a region; **divergence** is airflow out of a region. - Global circulation includes rising warm, moist air near the equator and descending drier air near 30 degrees latitude. Descending air contributes to the subtropical desert belts. ### Jet streams **Jet streams** are narrow, fast-flowing westerly winds near the tropopause, where air masses of different temperatures meet. They steer storms and influence severe-weather patterns. - The **polar jet stream** averages about 10 km in altitude and is generally stronger because it lies along a sharp boundary between cold polar air and warmer air to the south. - The **subtropical jet stream** averages about 13 km in altitude. - The polar jet shifts south in winter and north in summer. This seasonal shift helps move the main zone of U.S. thunderstorm and tornado activity northward in late winter, spring, and early summer. - Ridges and troughs in the jet stream cause it to meander north and south, helping create areas of rising and sinking air. ### Stability and the Coriolis effect - **Atmospheric stability** describes whether an air parcel resists vertical movement or continues rising or sinking. - Air is unstable when warm or moist, relatively light air lies beneath denser cold or dry air. Unstable air can rise, supporting thunderstorms and tornadoes. - The **Coriolis effect** is the apparent deflection of moving air caused by Earth's rotation. Moving air is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. ### Fronts A **front** is a boundary between air masses with different properties, commonly temperature and density. The warmer air is lifted over denser cold air. | Front | Movement and typical weather | |----------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------| | **Cold front** | Advancing cold air undercuts warm air along a steep boundary, forcing rapid uplift that can produce strong updrafts, clouds, and heavy precipitation. | | **Warm front** | Advancing warm air rises gradually over retreating cold air; cloud formation and precipitation are often more widespread and less intense. | | **Stationary front** | Boundary moves little and can remain in place for hours or days, allowing repeated precipitation. | | **Occluded front** | A faster cold air mass overtakes another cool air mass, lifting warm air above the frontal boundary. | ### Key terms - **Atmospheric pressure:** Force exerted by the weight of air above a location. - **Convergence / divergence:** Airflow into / out of a region. - **Jet stream:** Narrow, fast westerly wind near the tropopause. - **Atmospheric stability:** Tendency of air parcels to resist or continue vertical motion. - **Coriolis effect:** Apparent deflection of moving air due to Earth's rotation. - **Front:** Boundary between contrasting air masses. - **Ridge / trough:** Elongated high- / low-pressure pattern aloft that bends the jet stream. ### Section 9.4 review questions 1. Why does atmospheric pressure decrease with altitude? 2. How do convergence, divergence, and vertical motion relate to high- and low-pressure systems? 3. What makes air stable or unstable? 4. How does the Coriolis effect influence air movement? 5. Why is the polar jet stream generally stronger than the subtropical jet stream? 6. How do cold, warm, stationary, and occluded fronts differ? ## 9.5 Hazardous Weather and Geographic Regions at Risk (LO:4 and LO:5) ### Section summary Severe weather occurs where particular combinations of moisture, temperature, pressure, wind, and air-mass movement develop. Hazards covered in this section include thunderstorms and their associated lightning, hail, tornadoes, and damaging winds; blizzards; ice storms; fog; drought; mountain windstorms; dust and sandstorms; and heat waves. Risk is unevenly distributed, and exposure and vulnerability influence whether a weather event becomes a disaster. ### Thunderstorms Thunderstorms require three basic conditions: 1. Warm, humid air in the lower atmosphere to supply moisture and energy. 2. A steep vertical temperature gradient, with colder air above warmer, moist air. 3. An updraft that lifts moist air to colder levels, where it cools and condenses. Thunderstorms occur worldwide, especially in the tropics. In North America, frequent thunderstorm days occur along the Rocky Mountain Range in Colorado and New Mexico and across Florida and the southern parts of Georgia, Alabama, Mississippi, and Louisiana. Thunderstorms can occur in nearly every part of the United States and Canada. Thunderstorms commonly form along cold fronts and during afternoon or evening heating in spring and summer. A typical storm develops through three stages: 1. **Cumulus stage:** Updrafts lift moist air; condensation forms and builds a cumulonimbus cloud. Latent heat released by condensation helps the air rise. 2. **Mature stage:** Falling precipitation and downdrafts develop alongside updrafts. Heavy rain, hail, lightning, and strong gusts may occur. The cloud may spread into an anvil at the tropopause. 3. **Dissipating stage:** Downdrafts dominate, the supply of warm moist air is cut off, and precipitation and cloud growth weaken. Most single-cell air-mass thunderstorms last less than an hour. The National Weather Service definition cited in the textbook classifies a thunderstorm as severe if it produces winds above 93 km/hr, hail larger than 1.9 cm, or a tornado. ### Severe thunderstorm organization and winds Severe thunderstorms can persist and regenerate when atmospheric conditions support them. Important ingredients include abundant low-level water vapor, strong updrafts, dry air above moist air, and especially **vertical wind shear**: a change in wind speed or direction with altitude. | Type | Organization and hazard | |---------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------| | **Mesoscale convective system (MCS)** | Cluster of storm cells that can regenerate as downdrafts from one cell trigger new cells nearby; may persist for 12 hours or more. | | **Squall line** | Long, linear belt of thunderstorms, often hundreds of kilometers long; can produce damaging wind and tornadoes. | | **Supercell** | Large, violent storm with a rotating updraft, or **mesocyclone**; a major source of large tornadoes. Often 20-50 km across and lasts 2-4 hours. | Thunderstorm downdrafts can create straight-line windstorms. A **derecho** is a widespread damaging wind event associated with a line of storms, with a damage path at least about 400 km long. Smaller downbursts called **microbursts** are especially hazardous to aircraft. ### Lightning and hail - **Lightning** is an electrical discharge produced by charge separation in a storm cloud or between a cloud and the ground. Most lightning occurs within clouds, but cloud-to-ground strikes can kill, injure, start fires, and damage infrastructure. The chapter emphasizes that lightning survivors may experience serious long-term health effects. - Charge separation in cumulonimbus clouds is associated with interactions between ice crystals and graupel (small hail-like ice particles). A descending stepped leader and ascending streamers connect to form the lightning channel; the return stroke produces the visible flash. Rapid heating of the air produces thunder. - Safety message from the chapter: **“If you see it, flee it; if you hear it, clear it.”** - **Hail** forms when strong thunderstorm updrafts carry ice particles repeatedly through layers of supercooled water, adding concentric layers of ice. Large hail damages roofs, vehicles, crops, and people. The textbook identifies the Great Plains, especially northeastern Colorado and southeastern Wyoming, and the Calgary region as North American hail-risk areas. ### Tornadoes A **tornado** is a violently rotating column of air extending from a cloud to the ground. A funnel cloud that does not touch the ground is not yet a tornado. Tornadoes may develop near a rotating wall cloud in a supercell, but not every mesocyclone or wall cloud produces a tornado, and some tornadoes form without an obvious one. Typical tornadoes are tens of meters in diameter, have wind speeds from about 65 km/hr to over 450 km/hr, travel around 6-8 km, and last only a few minutes. Exceptional tornadoes can remain on the ground much longer and travel hundreds of kilometers. Tornadoes are rated after damage surveys on the **Enhanced Fujita (EF) Scale**, from EF0 to EF5. The rating is an estimate based on damage indicators, not a direct measurement of wind speed. - The United States has the world's greatest tornado frequency, with the Great Plains' “Tornado Alley” at especially high risk; tornadoes also occur widely from Florida and Texas northward through the central and eastern states. - Tornado risk in Canada is concentrated in regions including Alberta, southern Ontario, southeastern Quebec, and parts of the Prairie provinces. - Tornadoes are most common in spring and summer and often form in late afternoon or evening. - **Waterspouts** are rotating columns over water. Many are weaker than strong land tornadoes, but they remain hazardous. ### Winter storms, fog, drought, windstorms, dust, and heat | Hazard | Conditions and main effects | |------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | **Blizzard** | Falling or blowing snow combined with strong winds and prolonged low visibility. A ground blizzard can form when wind lifts old snow, even without new snowfall. Wind chill increases danger. North American risk areas include the Great Plains, Great Lakes, Northeast, Atlantic Canada, and eastern Arctic. | | **Ice storm** | Freezing rain develops when snow melts in a warm layer aloft, then supercooled drops pass through a shallow layer of cold air and freeze on contact with surfaces. Ice loading can break trees and power lines and make travel dangerous. Higher-risk regions include the Columbia River Valley, south-central Great Plains, Ohio River Valley, Mid-Atlantic and New England, and parts of eastern Canada. | | **Fog** | A cloud at ground level that becomes hazardous when it sharply reduces visibility. It forms when air cools to condensation or when water vapor is added to cool air. Fog-prone North American areas include Pacific, New England, and Atlantic Canadian coasts and Appalachian valleys. | | **Drought** | Extended unusually low precipitation creates a temporary shortage of water for people, animals, and plants. Effects include crop stress, water shortages, and reduced hydropower. Semiarid regions and the western United States are especially exposed. | | **Mountain windstorm** | Strong downslope winds on the lee side of mountains or glacial ice fields. Chinooks occur east of the Rockies; Santa Ana winds occur west of Southern California's Transverse Ranges. Winds can damage buildings and trees and contribute to wildfires. | | **Dust storm** | Strong winds suspend fine particles and reduce visibility; dust can affect health and travel and be transported long distances. Dust and sandstorms are common in midlatitude semiarid and arid regions. The 1930s Dust Bowl combined drought with exposed, eroding cropland in the southern High Plains. | | **Sandstorm** | Bouncing sand grains in a near-surface cloud, usually in deserts; unlike fine dust, sand generally does not rise far above the ground and can abrade surfaces. | | **Heat wave** | A prolonged period of heat that is hotter and longer than normal. Stagnant high-pressure ridges, drought, and urban heat islands can intensify impacts. The **heat index** combines temperature and humidity to estimate how hot conditions feel to the body. | For winter precipitation, the thickness of near-surface cold air helps determine whether falling precipitation reaches the ground as snow, sleet, freezing rain, or ordinary rain. A shallow cold layer favors freezing rain; a deeper layer allows raindrops to refreeze as sleet. ### Section 9.5 case studies - **Sarah Tessendorf, severe-storm meteorologist:** Tessendorf's research found that squall lines can produce tornadoes, including some violent ones, challenging the assumption that squall-line tornadoes are always weak. Her work also examined unusual lightning charge structures in High Plains storms. - **Michael Utley, lightning survivor:** Utley was struck during a golf tournament after a warning horn sounded. A companion's CPR helped save his life. The story illustrates the need to act promptly on lightning warnings and seek shelter. - **Tri-State Tornado, 1925:** Traveled about 349 km across Missouri, Illinois, and Indiana in 3.5 hours, killed at least 695 people, and injured more than 2,000. Lack of forecasting and warnings, building collapse, and flying debris contributed to the extraordinary losses. - **Northeastern ice storm, 1998:** Freezing rain persisted for six days, killing at least 45 people and cutting power to more than 5.2 million. Damage exceeded $6.2 billion, mostly in Canada. The event exposed the vulnerability of power, water, telecommunications, and supply systems to prolonged outages. - **European heat wave, 2003:** The hottest European summer in more than 500 years, according to the textbook, killed more than 30,000 people, including more than 14,800 in France. Drought, forest fires, urban heat, vulnerable populations, and limited heat-warning systems contributed to the disaster. Climate models cited in the chapter estimated that human greenhouse-gas emissions doubled the probability of an event of that magnitude. ### Key terms - **Vertical wind shear:** Change in wind speed or direction with altitude. - **Mesocyclone:** Rotating updraft in a supercell thunderstorm. - **Derecho:** Widespread, damaging straight-line wind event associated with thunderstorms. - **Microburst:** Small, intense thunderstorm downdraft that spreads damaging winds near the surface. - **EF Scale:** Enhanced Fujita rating based on damage surveys and estimated tornado winds. - **Blizzard:** Snowstorm with strong winds and prolonged low visibility. - **Wind chill:** The cooling effect of wind on exposed skin. - **Freezing rain:** Supercooled rain that freezes on contact with cold surfaces. - **Drought:** Extended period of unusually low precipitation causing water shortage. - **Heat index:** Apparent heat estimated from air temperature and relative humidity. - **Urban heat island:** Higher temperatures in a city than in surrounding rural areas. ### Section 9.5 review questions 1. What conditions are needed to form a thunderstorm? Describe its three stages. 2. How do MCSs, squall lines, and supercells differ? 3. What is vertical wind shear, and why is it important to severe storms? 4. How do lightning and hail form, and what hazards do they create? 5. How are tornadoes defined and rated? What is the difference between a funnel cloud and a tornado? 6. Compare blizzards, ice storms, fog, drought, mountain windstorms, dust storms, and heat waves. 7. How do wind chill and heat index differ? 8. What factors contributed to the severity of the 1998 ice storm and 2003 European heat wave? ## 9.6 Human Interaction with Weather (LO:6) ### Section summary Weather is a natural process, but human land use, infrastructure, settlement patterns, and climate change influence exposure and consequences. People can increase risk by exposing soil to wind erosion, placing vulnerable housing in high-wind areas, concentrating heat in cities, and relying on infrastructure with little redundancy. ### Ways people influence weather-related risk - Leaving cropland bare after harvest increased wind erosion and dust storms during the Dust Bowl. - Mobile homes and other vulnerable buildings in tornado- and wind-prone areas can experience greater damage and loss of life. - Pavement, dense development, waste heat, and sparse vegetation intensify the **urban heat island effect**. Cities may be several degrees warmer than nearby countryside; the chapter notes that local differences can reach about 12 degrees C in some settings. - Trees, parks, vegetated roofs, light-colored roofs, and permeable pavement can reduce urban heat accumulation. - Reliance on electricity, pumps, telecommunications, and just-in-time supplies can turn a storm into a prolonged social and economic disruption if systems fail. - Climate-model projections discussed in the textbook indicate that warming is likely to increase heat extremes and intense precipitation in many areas, increase drought risk in some continental interiors, and increase wind and precipitation intensities in tropical cyclones. The effects on tornadoes, thunderstorms, hail, and lightning remain less certain in the chapter. ### Case study: Europe and the 2003 heat wave The heat wave illustrates the interaction between climate, cities, and vulnerability. Urban areas trapped heat and accumulated air pollution. Many victims were elderly or otherwise vulnerable, some were socially isolated, and many services were less available during the August holiday period. Heat-health warning systems, cooling access, public education, and checking on vulnerable residents are important adjustments. ### Section 9.6 review questions 1. How did agricultural practices contribute to Dust Bowl dust storms? 2. How can development and building type change tornado losses? 3. What causes the urban heat island effect, and how can cities reduce it? 4. How may climate change influence different severe-weather hazards, and where is uncertainty greatest? 5. How did social vulnerability and infrastructure affect the 2003 European heat-wave impacts? ## 9.7 Linkages with Other Hazards (LO:7) ### Section summary Severe weather can trigger or intensify other hazards. The strength of these linkages depends on storm movement, rainfall, ground conditions, fuel moisture, and human exposure. ### Important hazard linkages - Slow-moving thunderstorms or storms repeatedly tracking along a stationary front can produce intense rainfall and flash flooding. The 2016 Louisiana event described in the chapter brought more than 61 cm of rain in some locations over a week. - Thunderstorms produce lightning, the primary natural ignition source for wildfires. Lightning starts a fire only when the strike and fuel conditions are suitable; drought and dry vegetation make spread more likely. - Drought can worsen heat waves, reduce water supplies, and increase wildfire risk. Heat and drought can also stress agriculture and ecosystems. - Dust storms and sandstorms reduce visibility, cause road crashes, affect respiratory health, and transport particles over long distances. - Ice storms and blizzards can cause hypothermia, transportation accidents, power failure, and interruption of water, communications, health care, and supply chains. - Severe weather is connected with tropical and extratropical cyclones; those broader linkages are developed further in Chapter 10. - Climate change can alter the frequency or intensity of several weather hazards and thus affect linked hazards over time. ### Section 9.7 review questions 1. How can slow-moving thunderstorms produce flash floods? 2. How do thunderstorms, lightning, drought, and wildfires interact? 3. Give examples of how a single weather event can cause infrastructure failure and cascading social impacts. 4. How can climate change alter linkages among drought, heat, dust, fire, and flooding? ## 9.8 Natural Service Functions of Severe Weather (LO:8) ### Section summary Severe weather can be hazardous while also providing natural services. Many benefits occur over long time scales and may be less visible than immediate damage. ### Natural and human services - Thunderstorms, snowstorms, and tropical storms move water through the hydrologic cycle and can provide the primary water supply for some regions. - Snowpack and seasonal rainfall replenish water supplies and reduce vulnerability to drought. - Lightning initiates natural fires that help maintain prairie, tundra, and forest ecosystems. - Windstorms topple dead or diseased trees; fallen material returns nutrients to soils, while new forest openings create habitat. - Ice storms can be part of ecological disturbance cycles that increase forest diversity. - Clouds, lightning, and snowfall have aesthetic and recreational value for people. Natural services do not make severe weather harmless. The same storm that supplies water or renews habitat can cause death, damage, and disruption. ### Section 9.8 review questions 1. What ecosystem services can result from lightning, windstorms, and ice storms? 2. How do snowstorms and seasonal rains help reduce drought vulnerability? 3. Why can a natural process provide services and still be a hazard to people? ## 9.9 Minimizing Severe Weather Hazards (LO:9) ### Section summary People cannot control the atmosphere, but forecasting, mitigation, preparedness, risk communication, and insurance can reduce losses. Forecasts remain uncertain, so effective warning systems and personal plans must account for both false alarms and events that develop quickly. ### Forecasting and warnings - Satellites, computer models, weather stations, and Doppler radar improve observation and short-term prediction. - Doppler radar detects movement toward or away from the radar through changes in the returned signal. It can identify rotation such as a mesocyclone and support tornado warnings, sometimes with lead times up to about 30 minutes. - A **watch** means that conditions are favorable and a hazard may develop; people should monitor information and be ready to act. - A **warning** means that a hazard has been observed or detected and people in the affected area should take immediate protective action. - Repeated warnings that do not result in a local event can contribute to complacency. Clear communication and appropriate public understanding are essential. ### Mitigation and preparedness - **Mitigation** consists of long-term actions that reduce potential deaths, injuries, and damage. Examples include wind-resistant construction, tornado shelters and safe rooms, resilient utilities, redundant communications, warning systems, and appropriate insurance coverage. - **Preparedness** consists of plans and actions taken before or as a hazard approaches. Know local hazards and shelter locations, keep emergency supplies, monitor official alerts, wear appropriate clothing, and adjust travel plans. - Critical infrastructure needs backup power and redundancy. Pump stations can fail when the grid is down; multiple communication systems are more resilient than reliance on a single network. - Review insurance carefully. Standard policies may exclude hazards such as flooding, requiring separate coverage. ### Personal adjustments - For tornadoes and severe storms, identify a safe shelter before a warning. A designated safe room or sturdy shelter is preferable to trying to outrun a tornado by car. - During heat waves, reduce direct sun exposure, use air conditioning or cooling centers, hydrate, wear light clothing, and check on older, ill, isolated, or otherwise vulnerable people. Never leave children or pets in a vehicle. - In cold, wet, and windy conditions, dress to prevent heat loss and recognize hypothermia signs such as shivering, poor coordination, sluggishness, and confusion. - In fog, blizzards, and dust storms, low visibility makes high-speed driving dangerous. Delay or modify travel rather than continuing into hazardous conditions. - Follow official alerts and instructions, and do not assume that an event will miss a location simply because it has been struck before or because forecasts sometimes produce false alarms. ### Applying the fundamental concepts: Moore, Oklahoma, tornadoes of 1999 and 2013 Moore illustrates all five fundamental concepts: 1. **Science helps predict hazards:** Weather satellites, mobile storm observations, Doppler radar, and storm prediction improved forecasts and warning lead time. A hook echo on radar can indicate a potentially tornadic supercell. 2. **Risk information can support decisions:** Tornadoes are relatively infrequent at a specific place on a given day, but Moore's 1999 EF5 demonstrated that rare events still create important risk. A similarly destructive tornado struck in 2013. 3. **Hazards are linked:** The 2013 severe-storm system produced tornadoes, heavy rain, hail, and flooding across the Great Plains. 4. **Humans can turn disasters into catastrophes:** Population growth increased exposure. Schools, homes, and a medical center lay in the path, and many homes lacked shelters. Clay-rich soil made below-ground shelters more expensive to engineer. 5. **Consequences can be minimized:** The 2013 warning lead time was longer than in 1999, and all 16 above-ground shelters in the tornado's path survived. However, the shelters were small, many schools lacked adequate safe space, and seven children died at Plaza Towers Elementary, which had not been fully evacuated. The chapter reports that the 1999 tornado killed 36 people and damaged or destroyed about 10,000 homes. The 2013 tornado killed 23 people and destroyed about 1,200 homes. These outcomes demonstrate the value of forecasting and warnings, but also the limits of warning when safe shelter is unavailable. ### Section 9.9 review questions 1. How do Doppler radar and satellites support severe-weather prediction? 2. Distinguish a watch from a warning. 3. How do mitigation and preparedness differ? 4. Give examples of ways to make buildings, utilities, and communication systems more resilient. 5. What should individuals do to prepare for severe storms, heat, cold, and low visibility? 6. What did Moore learn about the relationship among warnings, shelter access, population growth, and tornado losses? ## Connections among the Sections - **9.1 to 9.2:** Solar radiation is the main energy source; phase changes and heat transfer move energy through the atmosphere. - **9.2 to 9.3:** Uneven heating affects air temperature and humidity, while atmospheric structure and water vapor shape clouds and weather. - **9.3 to 9.4:** Temperature, pressure, and moisture in the atmosphere create circulation, stability, fronts, and jet streams. - **9.4 to 9.5:** Air-mass boundaries, instability, and wind shear produce the conditions for thunderstorms and other regional weather hazards. - **9.5 to 9.6:** Weather becomes a disaster when people and infrastructure are exposed and vulnerable; land use and climate change can alter impacts. - **9.5 to 9.7:** Severe storms can trigger floods, fires, infrastructure failures, and other hazards. - **9.7 to 9.8:** Weather can produce cascading damage while also providing water and ecosystem services. - **9.8 to 9.9:** Understanding both hazards and benefits supports forecasting, preparedness, and long-term mitigation. ## Chapter-Wide Comparison Questions - How do force, work, power, potential energy, kinetic energy, sensible heat, and latent heat relate? - How do conduction, convection, and radiation differ? - How do reflection, scattering, transmission, absorption, and emission affect Earth's energy balance? - How does albedo affect surface heating? - How do the troposphere, stratosphere, mesosphere, and thermosphere differ? - How do atmospheric pressure, temperature, convergence, divergence, and vertical motion interact? - How do the Coriolis effect and jet streams shape atmospheric circulation? - How do cold, warm, stationary, and occluded fronts differ? - What conditions produce thunderstorms, and how do their three stages differ? - How do MCSs, squall lines, and supercells differ? - How do lightning, hail, tornadoes, derechos, and microbursts form, and what hazards do they create? - How does the EF Scale rate tornadoes, and why is it based on damage surveys? - How do blizzards, ice storms, sleet, freezing rain, and ordinary rain differ? - How do fog, drought, mountain windstorms, dust storms, sandstorms, and heat waves affect people? - How do wind chill and heat index describe different forms of human heat stress? - How can human land use, infrastructure, urbanization, and climate change affect severe-weather risk? - How can severe weather trigger floods, wildfires, power failures, hypothermia, or other linked hazards? - What natural services can severe weather provide? - How do forecasting, watches, warnings, mitigation, preparedness, shelters, and insurance reduce losses? - What do the Moore tornadoes, Tri-State Tornado, 1998 ice storm, and 2003 European heat wave show about science and human decisions? ## Practice Questions 1. Define force, work, power, potential energy, kinetic energy, and heat energy. 2. Compare sensible and latent heat and explain how latent heat affects cloud development. 3. Describe conduction, convection, and radiation and give a weather-related example of each. 4. Explain Earth's energy balance and distinguish incoming shortwave from outgoing longwave radiation. 5. Explain albedo and predict how a dark surface and a light surface respond differently to sunlight. 6. Describe the four atmospheric layers and explain why the troposphere is central to weather. 7. Define relative humidity, atmospheric pressure, convergence, and divergence. 8. Explain atmospheric stability and the conditions that make air unstable. 9. Describe the Coriolis effect and the role of the polar and subtropical jet streams. 10. Compare cold, warm, stationary, and occluded fronts. 11. List the conditions needed for thunderstorms and describe the cumulus, mature, and dissipating stages. 12. Compare MCSs, squall lines, and supercells. Explain the role of vertical wind shear. 13. Explain how lightning and hail develop in thunderstorms. 14. Define a tornado and distinguish a funnel cloud, wall cloud, mesocyclone, and tornado. 15. Explain how tornado damage is classified on the EF Scale and why the rating is not a direct wind measurement. 16. Compare tornadoes, waterspouts, derechos, and microbursts. 17. Explain the atmospheric setup for blizzards, ice storms, freezing rain, and sleet. 18. Describe how fog forms and why it can be hazardous even though it is a low cloud. 19. Define drought, mountain windstorm, dust storm, sandstorm, heat wave, wind chill, and heat index. 20. Explain how the Dust Bowl and 1998 ice storm demonstrate human contributions to weather-related losses. 21. Describe how an urban heat island forms and how urban design can reduce it. 22. Explain how severe weather can cause flash floods and wildfires. 23. List natural service functions of thunderstorms, snowstorms, lightning, windstorms, and ice storms. 24. Distinguish severe-weather mitigation from preparedness. 25. Explain the difference between a weather watch and a warning and describe why warning response matters. 26. Use the Moore tornadoes, Tri-State Tornado, ice storm of 1998, or European heat wave of 2003 to explain how science and human decisions affect losses. ## Quick Review Checklist Before the quiz or test, make sure you can: - define energy, force, work, power, potential energy, kinetic energy, sensible heat, and latent heat; - distinguish conduction, convection, and radiation; - explain Earth's energy balance and the movement of shortwave and longwave radiation; - explain reflection, scattering, transmission, absorption, emission, and albedo; - describe the atmosphere's composition, humidity, and four major layers; - explain atmospheric pressure, convergence, divergence, stability, and fronts; - describe the Coriolis effect, global circulation, ridges, troughs, and jet streams; - list the conditions for thunderstorms and describe their development stages; - compare MCSs, squall lines, and supercells and explain vertical wind shear; - explain the formation and hazards of lightning, hail, tornadoes, derechos, and microbursts; - interpret the EF Scale and distinguish tornadoes from funnel clouds and waterspouts; - compare blizzards, ice storms, freezing rain, sleet, fog, drought, and heat waves; - distinguish mountain windstorms, dust storms, and sandstorms; - explain wind chill, heat index, and the urban heat island effect; - identify ways that land use, infrastructure, urbanization, and climate change affect weather losses; - trace severe-weather links to floods, wildfires, drought, power failure, and other hazards; - describe the natural services provided by weather and storms; - distinguish watches from warnings and mitigation from preparedness; - list personal and community actions that reduce severe-weather risk; and - use the Moore tornadoes, Tri-State Tornado, 1998 ice storm, and 2003 European heat wave examples to explain hazards and adjustments.