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

2. 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

3. 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

4. Definition: air pressure is the force exerted by the weight of a column of air on a surface
At sea level air pressure = 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

5. 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

6. 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

7. 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

8. 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

10. 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

11. 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

12. 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

13. 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

14. 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

16. 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

17. 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

18. 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

19. 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

20. 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

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

22. 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)

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 24.6 Predicting the Weather
Objectives
1. Interpret weather map features and describe the technology used to forecast weather

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. Recall that greenhouse gases include water vapor and CO2 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 CO2 levels increase enough that the temperature of the atmosphere rises

48. 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

49. 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