Pearson Prentice Hall Physical Science Concepts in Action

Pearson Prentice Hall Physical Science: Concepts in Action Chapter 24 Weather and Climate

24. 1 The Atmosphere • Objectives: • 1. Describe Earth’s atmosphere and explain how it is essential to life • 2. Describe the layers of the atmosphere and their properties

Atmosphere is Essential to Life • Earth’s atmosphere forms a protective boundary between Earth and space and provides conditions that are suitable for life • Earth’s atmosphere is a mixture of nitrogen, oxygen, water vapor and many other gases in which tiny solid and liquid particles are suspended • Earth’s atmosphere is composed of about 78% nitrogen and 21% oxygen • All other elements are called trace gases

• Definition: air pressure is the force exerted by the weight of a column of air on a surface • At sea level air pressure = 101. 3 k. Pa = 760 mm Hg = 1 atm • As altitude increases, air pressure and density decrease • Our air pressure in Reno is less than Sacramento or San Francisco • It is the main reason food takes longer to cook here • Definition: a barometer is an instrument used to measure air pressure

Layers of Atmosphere • There are 4 layers of atmosphere: • 1. troposphere is the atmospheric layer closest to Earth’s surface where nearly all weather occurs (it’s where we live) • Definition: weather is the condition of the atmosphere in a particular place at a particular time • The troposphere gets cooler with increasing altitude, but temperature inversions can occur • Temperature inversion is the atmospheric condition in which warm air traps cooler air near Earth’s surface

• 2. Stratosphere is the layer that contains the ozone layer and extends upward from the troposphere to an altitude of 50 km • Ozone is the form of atmospheric highly reactive oxygen gas that has three atoms per molecule – O 3 • The ozone layer is a protective layer when it is located in the stratosphere • Ozone absorbs harmful ultraviolet (UV) radiation from the sun when located in the stratosphere • Ozone is harmful to life when it is located in the troposphere

• Today, we know that man made chemicals can deplete the ozone layer • The ozone layer is located in the upper stratosphere and they absorb ultraviolet radiation from the sun preventing DNA damage to living organisms’ cells’ • Chlorofluorocarbons, CFCs, are believed to be the main culprit and they have been banned in the United States

• 3. mesosphere is the coldest layer located above the stratosphere • 4. thermosphere is the atmospheric layer above the mesosphere and starts at an altitude of about 80 km • The air is very thin in thermosphere • The outmost portion at about 80 km (298 mi) is the exosphere (not a distinct layer) where some gases escape Earth’s gravitational pull and exit into space • Ionosphere (not a distinct layer) is when solar energy absorbed in lower thermosphere & upper mesosphere forms electrically charged ions

• The ionosphere reflects radio waves, keeping them form escaping into space • Ionosphere is where the aurora can be seen around Earth’s poles • Auroras are light displays caused by the sun hitting atoms • Earth began to solidify 4. 4 billion years ago, and later bacteria came • Then, 2. 5 billion years ago, the first photosynthetic plants appeared and began to contribute oxygen to Earth’s atmosphere

• The atmosphere gradually accumulated oxygen until about 350 million years ago when the oxygen reached “modern” levels • Aerobic, oxygen breathing organisms evolved leading to a balance • Animals breathe oxygen by respiration and exhale carbon dioxide as waste • Plants use the carbon dioxide and oxygen is their waste product

24. 2 The Sun and the Seasons • Objectives: • 1. Describe how Earth moves through space and explain how seasons are caused by the tilt of Earth’s axis • 2. Explain why different latitude zones have different average temperatures

Seasons • Earth moves in 2 ways: rotation and revolution • Definition: rotation is the spinning of Earth on its axis • Definition: revolution is the movement of one body in space around another • Earth’s rotation causes day and night • Earth revolves around the sun • Scientists use line of latitude to mark out three different types of regions within which temperatures are generally similar: the tropic, temperate and polar zones

• The tropic zone is generally warm • The temperate zones are generally cooler than the tropics • The polar zones are at the north and south poles and are cold • The seasons are caused by the tilt of Earth’s axis as it moves around the sun • Earth’s tilt and rotation account for seasons • Earth is tilted 23. 5° from its perpendicular on its axis

• Definition: a solstice are the two days each year when the sun is directly overhead at 23. 5°N or 23. 5°S • The longest day of the year is the summer solstice, June 21 (the first day of summer) in the northern hemisphere • The shortest day is the winter solstice in the northern hemisphere, December 21(the first day of winter) • Definition: an equinox occurs when hours of daylight and nighttime are nearly equal • Twice per year the days have equal hours of daylight and night- the vernal equinox (first day of spring around March 21), and the autumnal equinox (first day of fall) occurring around September 22

24. 3 Solar Energy and Winds • Objectives: • 1. Describe the processes by which solar energy heats up the troposphere • 2. Identify local and global winds and explain how they are produced

Energy and the Troposphere • Some solar energy that reaches Earth’s atmosphere is reflected back, some is absorbed by the atmosphere and some is absorbed by Earth’s surface • Definition: The greenhouse effect is the process in which atmospheric gases trap some of the energy from the sun in the troposphere and keep Earth warm • Without the greenhouse effect Earth would have colder average temperatures • With too much of the effect Earth’s temperatures will rise

Local and Global Wind • Energy is transferred within the troposphere in 3 ways: radiation, convection and conduction • Winds are caused by differences in air pressure • Larger pressure differences produces stronger winds • Definition: a local wind is a wind that blows over a short distance

• The breezes that occur where land meets a large body of water are local winds • Definition: a sea breeze is the cooler air over the water that flows toward the land • Definition: a land breeze is the higher density cool air over land that moves toward water • Winds are named for the direction from which they originate (sea breezes start at the ocean and land breezes begin over land) • Definition: global winds are winds that blow over long distances from a specific direction • Global winds move in a circular band motion called convection cells

• Global winds are caused by unequal heating of Earth’s surface across a large region • Trade winds, westerlies and polar easterlies are global winds

• The direction of wind movement is influenced by Earth’s rotation in a phenomenon called the Coriolis effect • Definition: Coriolis effect is the change in the direction of an object’s path due to Earth’s rotation • Winds moving south from the equator move to the left (counter clockwise) while moving north in the northern hemisphere, winds curve to the right (clockwise)

• There is a global pattern to the wind • Temps at the equator tend to be warmer, so air there rises causing a low pressure belt • In the northern hemisphere, the air sinks creating a high pressure belt • Air flows from north to south, from high to low pressure converging at the poles in a low pressure belt • Each hemisphere completes 3 of these circulation pattern loops called convection cells

• Definition: a monsoon is a wind system that is characterized by seasonal reversal of direction • Monsoons are similar to sea and land breezes except they occur on a much larger scale and over a greater period of time • Definition: a jet stream is a belt of highspeed wind in the upper troposphere • Jet streams are caused by great differences in air pressure that develops over high altitudes

24. 4 Water in the Atmosphere • Objectives: • 1. Explain condensation in the atmosphere and describe the formation and characteristics of basic cloud forms • 2. Identify the common types of precipitation and explain how they form

Condensation and Basic Clouds • Definition: humidity is the amount of water vapor in the air • Definition: relative humidity is the ratio of the amount of water vapor in the air to the maximum amount of water vapor that could exist at that temperature • Relative humidity is always a percentage • Definition: dew point is the temperature at which the air becomes saturated with water vapor

• Water vapor typically condenses as dew, frost, clouds or fog • Definition: a cloud is a dense, visible mass of tiny water droplets or ice crystals that are suspended in the atmosphere • Definition: fog is a cloud that is near or touching the ground • Clouds form as warm, moist air rises and water vapor condenses in the atmosphere • There are three basic cloud types: stratus, cumulus and cirrus

• Cirrus are the highest (6000 – 11, 000 km above Earth) & are thin & wispy • Status are sheetlike & layered occurring between the surface to 6 km up • Cumulus clouds are white and fluffy with flat bottoms (the point where rising air begins to condense) forming from 500 m – 12 km above Earth • -nimbo or –nimbus added to a cloud’s name means that the cloud produces precipitation • Middle level clouds that occur at altitudes between 2000 – 6000 meters are given the prefix alto • Cirro- is used to describe high altitude clouds

Precipitation • The most common types of precipitation are rain, snow, hail, sleet and freezing rain • Rain usually forms in nimbostratus or cumulonimbus clouds • Def: Snow is actually ice crystals called snowflakes • Def: Hail is solid pieces of ice more than 5 mm in diameter • It comes from cumulonimbus clouds • Def: Sleet is ice particles less than 5 mm in diameter • Def: Freezing rain is rain that freezes after hitting the surface

24. 5 Weather Patterns • Objectives: • 1. Explain how air masses form and how they are classified • 2. Describe the four types of fronts, and the weather associated with each • 3. Describe cyclones and anticyclones • 4. Describe the major types of storms and how they are formed

Air Masses • An air mass forms when a large body of air becomes fairly stationary over a region of Earth’s surface or as air moves over a large, uniform region like an ocean • Meteorologists track weather by studying the movement of air masses • Air masses are large bodies of air with uniform temperature and moisture content • Air mass interactions have predictable effects on weather • Def: A front is the boundary between air masses of different densities

Four Types of Fronts • The four types of fronts are warm, cold, stationary and occluded • In a warm front a mass of warm air moves over a slower mass of cool air causing clouds to form as the warm front cools • As time passes, nimbostratus clouds may release snow or rain for one to two days

• In a cold front, the forward edge of the front moves under a slower moving mass of warm air which pushes the cold front up forming clouds sometimes producing high winds, thunderstorms and tornadoes • A stationary front occurs when two air masses meet & move side by side along the front producing conditions similar to a warm front • An occluded front forms when a warm air mass is caught between two cooler air masses • The colder air masses force the warm air mass to rise, trapping it between the two cold air masses

Cyclones and Anticyclones • Definition: a cyclone is a weather system with a center of low pressure • Cyclones are associated with clouds, precipitation, and stormy weather • Definition: a weather system with a swirling center of high air pressure is called an anticyclone • The weather associated with an anticyclone includes clear skies, very little precipitation and generally calm conditions

Storms • Definition: a thunderstorm is a small weather system that includes thunder and lightning • Lightning is a discharge of electrical energy • Thunder is the noise made when electrical charges move through the air along the path of the lightning • Thunderstorms form when columns of air rise within a cumulonimbus cloud • Twister is a common name for a tornado • Definition: a tornado is small but intense windstorm that takes the form of a rotating column of air that touches the ground

• Tornadoes are funnels of high-speed rotating wind that extend down from thunderclouds • On Earth they are most common in the United States in early spring and summer • They usually form along a front between cool, dry northern air and warm, moist southern air creating the rotation • A funnel cloud is a tapered column of water that is the beginning of a tornado • Thunderstorms and tornadoes are associated with cyclone of the middle latitudes • Tornadoes are dangerous and you should seek shelter or lie in a ditch if you are outside when one strikes

• Definition: a hurricane is a large tropical cyclone with winds of at least 74 mph • In the Caribbean they are called cyclones (Atlantic) & in the Indian Ocean they are called typhoons • In the northern hemisphere they typically occur during late summer and early fall • Hurricanes begin as tropical depressions from warm ocean water evaporating, vapor rising creating intense low pressure areas • Hurricanes are powered by energy released as water vapor condenses to form clouds • Its eye is calm and cloud-free

24. 6 Predicting the Weather • Objectives • 1. Interpret weather map features and describe the technology used to forecast weather

Forecasting • Definition: meteorology is the study of Earth’s atmosphere • Meteorologists use many technologies to help predict the weather, including Doppler radar, automated weather stations and high-speed computers • Doppler radar uses the Doppler effect • It bounces radio waves off particles of precipitation in moving storms and measures the frequency of the waves that return

• Weather satellites have been placed in Earth’s orbit since the 1960 s • The satellites can “see” storm formation including hurricanes and measure cloud cover, humidity, temperature and wind speed • Weather stations have sensors that measure temperature, precipitation, wind speed and wind direction • High-speed computers analyze weather information and scientists make predictions about the forecast

Weather Maps • Weather maps are used by meteorologists to prepare forecasts • The maps have symbols for precipitation, wind speed, cloud coverage, fronts & so on • Def: Isobars are lines drawn on a weather map connecting points of equal barometric or atmospheric pressure • The wind directions are slightly across the isobars due to the Coriolis effect • Def: isotherms are lines on a map that connect points of equal air pressure

24. 7 Climate • Objectives: • 1. Distinguish between weather and climate and describe the main factors that affect a region’s climate • 2. Compare climate variations due to natural and human causes

Weather versus Climate • Definition: Climate is the general weather conditions over many years • It is the average weather of a region • Temperatures tend to be higher around the equator producing a warm climate • The two main factors that determine a region’s climate are temperature and precipitation • Factors that affect a region’s temperature include its latitude, distance from large bodies of water, ocean currents and altitude

• Factors that affect a region’s precipitation include its latitude, the distribution of air pressure systems and global winds, and the existence of a mountain barrier • Definition: a desert is a dry region with less than 25 cm of rain per year • We live in a high, cold desert • Def: Topography is the surface features of the Earth • It is hills, mountains, valleys, and flat surface • Mountains an have a profound effect on climate

• Tall mountains force air over them while rising air forms clouds causing precipitation on the side where the air was rising and cool, dry air on the other side of the mountain where the air descends • Climates change over the long term, and they vary somewhat over the short term • Def: ice ages are periods when climates were colder than usual and glaciers covered a large portion of Earth’s surface • There have been many ice ages on Earth

• Def: El Niňo is a short-term natural climate variation that occurs every 8 years off the coast of South America • El Niňo causes a periodic warming of the central and eastern Pacific Ocean disrupting the fishing industries for the countries off the western coast of South America • The mechanism is not well understood but ocean currents and wind patterns change at that time

• Recall that greenhouse gases include water vapor and CO 2 among others • The greenhouse effect is the process in which atmospheric gases trap some of the energy from the sun in the troposphere and keep Earth warm • Without the greenhouse effect Earth would have colder average temperatures • With too much of the effect Earth’s temperatures will rise • Def: global warming is a process in which CO 2 levels increase enough that the temperature of the atmosphere rises

• There has been a well- documented rise in the level of CO 2 in the last 100 years believed to have come from the burning of coal, oil and natural gas (hydrocarbon fossil fuels) • The Keeling graph has been tracking the CO 2 levels since the mid 1800 s • Some scientists think this rise in CO 2 levels is contributing to the greenhouse effect and might give rise to the phenomenon called global warming

• Global warming might cause ice caps to melt, oceans to rise droughts in some places • Global climate changes over time • There have been many ice ages on Earth which coincide with the sunspot cycle (as do warming cycles) • Increased carbon dioxide may eventually lead to a warming effect caused by the greenhouse effect • Earth’s climate will continue to change