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 kPa = 760mm 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 – O3

• 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 the 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 seasonsEarth’s tilt and rotation account for seasons• Earth is tilted 23.5° from its perpendicular Earth is tilted 23.5° from its perpendicular

on its axison 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, The longest day of the year is the summer solstice, June 21 (the first day of summer) in the northern June 21 (the first day of summer) in the northern hemispherehemisphere

• The shortest day is the winter solstice in the northern The shortest day is the winter solstice in the northern hemisphere, December 21(the first day of winter)hemisphere, December 21(the first day of winter)

• Definition: an equinox occurs when hours of daylight Definition: an equinox occurs when hours of daylight and nighttime are nearly equaland nighttime are nearly equal

• Twice per year the days have equal hours of daylight Twice per year the days have equal hours of daylight and night- the vernal equinox (first day of spring and night- the vernal equinox (first day of spring around March 21), and the autumnal equinox (first day around March 21), and the autumnal equinox (first day of fall) occurring around September 22of 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 high-speed 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 An air mass forms when a large body of air becomes

fairly stationary over a region of Earth’s surface or fairly stationary over a region of Earth’s surface or as air moves over a large, uniform region like an as air moves over a large, uniform region like an oceanocean

• Meteorologists track weather by studying the Meteorologists track weather by studying the movement of air massesmovement of air masses

• Air masses are large bodies of air with uniform Air masses are large bodies of air with uniform temperature and moisture contenttemperature and moisture content

• Air mass interactions have predictable effects on Air mass interactions have predictable effects on weatherweather

• Def: A front is the boundary between air masses of Def: A front is the boundary between air masses of different densitiesdifferent 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 In a warm front a mass of warm air

moves over a slower mass of cool air moves over a slower mass of cool air causing clouds to form as the warm causing clouds to form as the warm front coolsfront cools• As time passes, nimbostratus clouds As time passes, nimbostratus clouds

may release snow or rain for one to may release snow or rain for one to two daystwo days

• In a cold front, the forward edge of the front In a cold front, the forward edge of the front moves under a slower moving mass of warm air moves under a slower moving mass of warm air which pushes the cold front up forming clouds which pushes the cold front up forming clouds sometimes producing high winds, sometimes producing high winds, thunderstorms and tornadoesthunderstorms and tornadoes

• A stationary front occurs when two air masses A stationary front occurs when two air masses meet & move side by side along the front meet & move side by side along the front producing conditions similar to a warm frontproducing conditions similar to a warm front

• An occluded front forms when a warm air mass An occluded front forms when a warm air mass is caught between two cooler air massesis caught between two cooler air masses

• The colder air masses force the warm air mass The colder air masses force the warm air mass to rise, trapping it between the two cold air to rise, trapping it between the two cold air massesmasses

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 Definition: a thunderstorm is a small weather

system that includes thunder and lightningsystem that includes thunder and lightning• Lightning is a discharge of electrical energyLightning is a discharge of electrical energy• Thunder is the noise made when electrical Thunder is the noise made when electrical

charges move through the air along the path charges move through the air along the path of the lightningof the lightning

• Thunderstorms form when columns of air rise Thunderstorms form when columns of air rise within a cumulonimbus cloudwithin a cumulonimbus cloud

• Twister is a common name for a tornadoTwister is a common name for a tornado• Definition: a tornado is small but intense Definition: a tornado is small but intense

windstorm that takes the form of a rotating windstorm that takes the form of a rotating column of air that touches the groundcolumn of air that touches the ground

• Tornadoes are funnels of high-speed rotating Tornadoes are funnels of high-speed rotating wind that extend down from thundercloudswind that extend down from thunderclouds

• On Earth they are most common in the United On Earth they are most common in the United States in early spring and summerStates in early spring and summer

• They usually form along a front between cool, They usually form along a front between cool, dry northern air and warm, moist southern air dry northern air and warm, moist southern air creating the rotationcreating the rotation

• A funnel cloud is a tapered column of water that A funnel cloud is a tapered column of water that is the beginning of a tornadois the beginning of a tornado

• Thunderstorms and tornadoes are associated Thunderstorms and tornadoes are associated with cyclone of the middle latitudeswith cyclone of the middle latitudes

• Tornadoes are dangerous and you should seek Tornadoes are dangerous and you should seek shelter or lie in a ditch if you are outside when shelter or lie in a ditch if you are outside when one strikesone strikes

• Definition: a hurricane is a large tropical Definition: a hurricane is a large tropical cyclone with winds of at least 74 mphcyclone with winds of at least 74 mph

• In the Caribbean they are called cyclones In the Caribbean they are called cyclones (Atlantic) & in the Indian Ocean they are (Atlantic) & in the Indian Ocean they are called typhoonscalled typhoons

• In the northern hemisphere they typically In the northern hemisphere they typically occur during late summer and early fall occur during late summer and early fall

• Hurricanes begin as tropical depressions from Hurricanes begin as tropical depressions from warm ocean water evaporating, vapor rising warm ocean water evaporating, vapor rising creating intense low pressure areascreating intense low pressure areas

• Hurricanes are powered by energy released as Hurricanes are powered by energy released as water vapor condenses to form cloudswater vapor condenses to form clouds

• Its eye is calm and cloud-freeIts 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 1960s

• 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 Weather maps are used by meteorologists to

prepare forecastsprepare forecasts• The maps have symbols for precipitation, The maps have symbols for precipitation,

wind speed, cloud coverage, fronts & so onwind speed, cloud coverage, fronts & so on• Def: Isobars are lines drawn on a weather Def: Isobars are lines drawn on a weather

map connecting points of equal barometric or map connecting points of equal barometric or atmospheric pressureatmospheric pressure

• The wind directions are slightly across the The wind directions are slightly across the isobars due to the Coriolis effectisobars due to the Coriolis effect

• Def: isotherms are lines on a map that Def: isotherms are lines on a map that connect points of equal air pressureconnect 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 Climate is the general weather

conditions over many yearsconditions over many years• It is the average weather of a regionIt is the average weather of a region• Temperatures tend to be higher around the Temperatures tend to be higher around the

equator producing a warm climateequator producing a warm climate• The two main factors that determine a The two main factors that determine a

region’s climate are temperature and region’s climate are temperature and precipitationprecipitation

• Factors that affect a region’s temperature Factors that affect a region’s temperature include its latitude, distance from large bodies include its latitude, distance from large bodies of water, ocean currents and altitudeof 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 Def: Topography is the surface features of the

EarthEarth• It is hills, mountains, valleys, and flat surfaceIt is hills, mountains, valleys, and flat surface• Mountains an have a profound effect on Mountains an have a profound effect on

climate climate

• Tall mountains force air over them while Tall mountains force air over them while rising air forms clouds causing precipitation rising air forms clouds causing precipitation on the side where the air was rising and on the side where the air was rising and cool, dry air on the other side of the cool, dry air on the other side of the mountain where the air descendsmountain where the air descends

• Climates change over the long term, and Climates change over the long term, and they vary somewhat over the short termthey vary somewhat over the short term

• Def: ice ages are periods when climates Def: ice ages are periods when climates were colder than usual and glaciers were colder than usual and glaciers covered a large portion of Earth’s surfacecovered a large portion of Earth’s surface

• There have been many ice ages on EarthThere have been many ice ages on Earth

• Def: El Niňo is a short-term natural climate Def: El Niňo is a short-term natural climate variation that occurs every 8 years off the variation that occurs every 8 years off the coast of South Americacoast of South America• El Niňo causes a periodic warming of the El Niňo causes a periodic warming of the

central and eastern Pacific Ocean central and eastern Pacific Ocean disrupting the fishing industries for the disrupting the fishing industries for the countries off the western coast of South countries off the western coast of South AmericaAmerica• The mechanism is not well understood but The mechanism is not well understood but

ocean currents and wind patterns change ocean currents and wind patterns change at that time at that time

• Recall that greenhouse gases include water vapor Recall that greenhouse gases include water vapor and COand CO22 among others 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 CODef: global warming is a process in which CO22 levels increase enough that the temperature of levels increase enough that the temperature of the atmosphere risesthe atmosphere rises

• There has been a well- documented rise in the level of CO2 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 CO2 levels since the mid 1800s

• Some scientists think this rise in CO2

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 timeGlobal climate changes over time• There have been many ice ages on Earth There have been many ice ages on Earth

which coincide with the sunspot cycle which coincide with the sunspot cycle (as do warming cycles)(as do warming cycles)• Increased carbon dioxide may Increased carbon dioxide may

eventually lead to a warming effect eventually lead to a warming effect caused by the greenhouse effectcaused by the greenhouse effect• Earth’s climate will continue to changeEarth’s climate will continue to change