Weather and Climate
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Weather and Climate Dana Desonie, Ph.D. Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHOR Dana Desonie, Ph.D. To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2014 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Com- mons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: October 29, 2014 www.ck12.org Chapter 1. Weather and Climate CHAPTER 1 Weather and Climate CHAPTER OUTLINE 1.1 Introduction to Weather 1.2 Humidity 1.3 Clouds 1.4 Fog 1.5 Precipitation 1.6 Air Masses 1.7 Weather Fronts 1.8 Thunderstorms 1.9 Tornadoes 1.10 Mid-Latitude Cyclones 1.11 Hurricanes 1.12 Blizzards 1.13 Heat Waves and Droughts 1.14 Collecting Weather Data 1.15 Weather Maps 1.16 Weather versus Climate 1.17 Effect of Latitude on Climate 1.18 Effect of Atmospheric Circulation on Climate 1.19 Effect of Continental Position on Climate 1.20 Effect of Altitude and Mountains on Climate 1.21 Climate Zones and Biomes 1.22 Tropical Moist Climates 1.23 Dry Climates 1.24 Temperate Climates 1.25 Continental Climates 1.26 Polar Climates 1.27 Climate Change in Earth History 1.28 Short-Term Climate Change 1.29 Global Warming 1.30 Causes and Effects of Global Warming 1.31 Impact of Continued Global Warming 1.32 Reducing Greenhouse Gas Pollution 1.33 References 1 www.ck12.org Introduction What’s the difference between weather and climate? When you think of Greece, you probably think of sunshine and white buildings. Maybe a beautiful beach. All of these are typical of Greece, which has a warm Mediterranean climate. In the winter, snow sometimes blankets the highlands. Rarely, though, it snows in the Greek lowlands. Snow is so uncommon in Athens that when it happens it brings the city to a standstill. The Acropolis sits on a rocky outcrop above Athens. It’s beautiful, but rare, to see this ancient ruin covered with snow. The weather in the photo on the right is cold and snowy, but the climate is still Mediterranean. Climate is the long-term average of weather. 2 www.ck12.org Chapter 1. Weather and Climate 1.1 Introduction to Weather • Learn what factors make up weather. • Understand what causes weather. What’s the weather like? The United States is a big country. With two coasts and a large land mass in between, there’s a chance for every kind of weather. In the next few sections we’ll visit places that have the type of weather we’re interested in studying. What is Weather? All weather takes place in the atmosphere. Nearly all of it in the lower atmosphere. Weather refers to the conditions of the atmosphere at a given time and place. Climate is the average of weather over a long time. Imagine your grandmother who lives in a distant place calls you up. She asks what your weather is like today. What would you say? Is it warm or cold? Sunny or cloudy? Calm or windy? Clear or rainy? What features of weather are important to mention? A location’s weather depends on: • air temperature. • air pressure. • fog. • humidity. • cloud cover. 3 1.1. Introduction to Weather www.ck12.org • precipitation. • wind speed and direction. All of these characteristics are directly related to the amount of energy that is in the system, and where that energy is. The ultimate source of this energy is the Sun. Weather is what we experience from day to day, or minute to minute. Weather can change rapidly. What Causes Weather? Weather occurs because of unequal heating of the atmosphere. The source of heat is the Sun. The general principles behind weather can be stated simply: • The Sun heats Earth’s surface more in some places than in others. • Where it is warm, heat from the Sun warms the air close to the surface. If there is water at the surface, it may cause some of the water to evaporate. • Warm air is less dense, so it rises. When this happens, more dense air flows in to take its place. The flowing surface air is wind. • The rising air cools as it goes higher in the atmosphere. If it is moist, the water vapor may condense. Clouds may form, and precipitation may fall. Vocabulary • climate: Long-term average of weather for a region. Climate changes relatively slowly. • weather: Temporary state of the atmosphere in a region. Summary • A region’s weather depends on its air temperature, air pressure, humidity, precipitation, wind speed and direction, and other factors. • Climate is the long-term average of weather. • Weather can change in minutes, but climate changes very slowly. Explore More Use the resource below to answer the questions that follow. • Climate and Weather at http://video.nationalgeographic.com/video/science/earth-sci/climate-weather-sci/ 1. What is climate? 2. How many climate zones are there? List examples. 3. What did climate determine in the past? 4. Why doesn’t climate have as much influence today? 5. What is weather? 6. What problems can severe weather cause? 7. Why is an accurate weather forecast important? 8. What tools do meteorologists use? 4 www.ck12.org Chapter 1. Weather and Climate Explore More Answers 1. Climate is the average of weather over a long period of time. 2. There are six major climate zones; examples include the Mediterranean, the arid desert and the frozen tundra. 3. Climate determined where people would settle. 4. Now we can alter our indoor environment so that we don’t need to survive weather extremes. 5. Weather is the day-to-day state of the atmosphere at a particular place and time. 6. Severe weather can destroy houses and other property, make transportation difficult and ruin crops, besides killing people and other animals. 7. If people have an accurate forecast they can prepare for severe weather or even evacuate the area. 8. Meteorologists use computers to do weather maps and modeling, radar to image storms, satellites for monitor- ing weather like cloud cover, precipitation, lighting, ocean temperature; plus planes can go into severe storms to study them. Review 1. Compare and contrast weather and climate. 2. What factors account for a location’s weather? 3. Describe how unequal heating causes weather. Review Answers 1. Weather is the condition of the atmosphere at the moment. Climate is weather averaged over a longer period of time. 2. temperature, precipitation, wind, clouds 3. A region receives more sunlight and therefore becomes warmer. The warmer air rises, and air from elsewhere flows in to take its place, creating wind. If the rising air is moist, it may begin to precipitate. 5 1.2. Humidity www.ck12.org 1.2 Humidity • Explain how humidity affects temperature. • Understand humidity, relative humidity, and dew point. Would you rather spend a summer day in Phoenix or in Houston? People who live in Phoenix, Arizona are told that summer isn’t so bad because "it’s a dry heat." What does that mean? Imagine that both Phoenix and Houston have a temperature of 90°F. In Phoenix, the relative humidity is 20%. In Houston, the relative humidity is 90%. So in Phoenix it feels like it’s 90°. But in Houston it feels like it’s 122! Of course in Phoenix in July, the average high temperature is 106°. That’s hot, dry or not! Humidity Humidity is the amount of water vapor in the air. High humidity increases the chances of clouds and precipitation. Relative Humidity Humidity usually refers to relative humidity. This is the percent of water vapor in the air relative to the total amount the air can hold. How much water vapor can the air hold? That depends on temperature. Warm air can hold more water vapor than cool air ( Figure 1.1). Humidity and Heat People often say, “it’s not the heat but the humidity.” Humidity can make a hot day feel even hotter. When sweat evaporates, it cools your body. But sweat can’t evaporate when the air already contains as much water vapor as it can hold. The heat index ( Figure 1.2) is a measure of what the temperature feels like because of the humidity.