1. Unit 5: Chapters 22, 23, 24, 25, and 3

2. SES5. Students will investigate the interaction of insolation and Earth systems to produce weather and climate.  a. Explain how latitudinal variations in solar heating create atmospheric and ocean currents that redistribute heat globally.  b. Explain the relationship between air masses and the surfaces over which they form.  c. Relate weather patterns to interactions among ocean currents, air masses, and topography.  d. Describe how temperature and precipitation produce the pattern of climate regions (classes) on Earth.  e. Describe the hazards associated with extreme weather events and climate change (e.g., hurricanes, tornadoes, El Niño/La Niña, global warming).  f. Relate changes in global climate to variation in Earth/Sun relationships and to natural and anthropogenic modification of atmospheric composition.

3. Chapter 3

4. Finding Locations on Earth: Latitude  A reference grid that is made up of additional circles is used to locate places on Earth‘s surface.  Halfway between the poles, a circle called the equator divides Earth into the North and Southern Hemispheres.  parallel any circle that runs east and west around Earth and that is parallel to the equator; a line of latitude  latitude the angular distance north or south from the equator; expressed in degrees

5. Latitude

6. Degrees of Latitude  Latitude is measured in degrees  the equator is 0° latitude.  the latitude of both the North Pole and the South Pole is 90°.  In actual distance, 1° latitude equals about 111 km. Minutes and Seconds  Each degree of latitude consists of 60 equal parts, called minutes. One minute (symbol: °) of latitude equals 1.85 km.  Each minute is divided into 60 equal parts, called seconds (symbol: °).

7. Longitude  East-west locations are established by using meridians.  meridian any semicircle that runs north and south around Earth from the geographic North Pole to the geographic South Pole; a line of longitude  longitude the angular distance east or west from the prime meridian; expressed in degrees

8. Longitude

9. Degrees of Longitude  prime meridian - 0° longitude and passes through Greenwich, England  International Date Line - The meridian opposite the prime meridian, halfway around the world, is labeled 180°. Distance Between Meridians  The distance covered by a degree of longitude depends on where the degree is measured. The distance measured by a degree of longitude decreases as you move from the equator toward the poles.

10. Chapter 22

11.  Atmosphere – layer of gases that surrounds Earth.  Composition  Most abundant elements in air are Nitrogen, Oxygen, and Argon  Nitrogen makes up 78% of Earth’s atmosphere  Oxygen makes up 21% of Earth’s atmosphere  Two most abundant compounds in air are CO 2 and H 2 O. Characteristics of the Atmosphere

12.  Ozone (O 3 ) in the Atmosphere  Ozone layer found in upper layer of the atmosphere and absorbs harmful ultraviolent radiation from the sun.  Damage to Ozone layer caused by release of Chlorofluorocarbons (CFCs), previously used in refrigerators and air conditioners, and nitrogen oxide from exhaust.

13.  Particulates in the Atmosphere  Tiny solid particles which may include volcanic dust, ash from fires, microscopic organisms, mineral particles lifted from soil by winds, pollen from plants, etc.

14.  Gases are held near the Earth’s surface by gravity  99% of the total mass of the atmosphere is held within 32km of Earth’s surface  Air molecules are compressed together and exert a force on any surface.  Pressure decreases as altitude increases  The pull of gravity is not as strong at higher altitudes, so the molecules are farther apart and exert less pressure  Measured with a barometer  Average atmospheric pressure at sea level is 1 atmospheres (atm) Atmospheric Pressure

15. Layers of the Atmosphere Distinctive pattern of temperature changes with increasing altitude caused by differences in absorption of solar energy.

16.  Troposphere  Closest to Earth’s surface  Extends to nearly 12km  Contains all water and carbon dioxide  All weather occurs here  Air is heated by thermal energy radiated from Earth’s surface  Temperature decreases with altitude

18.  Stratosphere  Extends to nearly 50km  Contains almost all of the ozone  Temperature increases with altitude as ozone absorbs solar radiation

19.  Mesosphere  Extends to about 80km  Temperature decreases with altitude to nearly -90°C  Thermosphere  Temperature increases with altitude because nitrogen and oxygen absorb solar radiation  Temperatures recorded at more than 1,000°C  Contains the Ionosphere  Atoms of gas molecules lose electrons producing ions and free electrons.  Reactions between solar radiation and ionosphere produce auroras.

21.  Radiation – all forms of energy that travel through space as waves known as the Electromagnetic Spectrum Solar Energy and the Atmosphere

23.  As solar radiation passes through the atmosphere  Shorter wavelengths (X-rays, gamma rays, and ultraviolet rays) are absorbed in the upper atmosphere  Longer wavelengths (infrared and visible light) that reach the lower atmosphere are absorbed by carbon dioxide, water vapor, and other molecules in the troposphere.  Scattering occurs when particles and gas molecules reflect and bend solar rays changing their direction, but not wavelength  Causes the sky to be blue and the sun to be red at sunrise and sunset.

25.  When solar radiation reaches Earth’s surface, it is either absorbed or reflected depending on the color, texture, composition, volume, mass, transparency, state of matter, and specific heat of the material.  Albedo is the solar radiation that is reflected by earth’s surface.  30% of the solar energy that reaches Earth’s atmosphere is reflected or scattered  Earth’s albedo is 0.3

26.  Snow and ice reflect 50 to 90%

27.  Forests reflect 5 to 10%

28.  Surfaces heated by incoming solar radiation convert the energy into infrared rays of longer- wavelengths and reemit it.  Those wavelengths of infrared rays are absorbed by carbon dioxide, water vapor, and other gas molecules in the atmosphere.  This absorption and release of energy keeps the earth’s surface warmer than it would be without an atmosphere and is known as the Greenhouse Effect

29.  Greenhouse Effect  Greenhouse Gases: naturally occurring gases that absorb solar radiation quickly, but release it slowly.  H 2 O  CO 2  Ozone  Methane

30. Human Impact on the Greenhouse Effect  Amount of Carbon Dioxide in the atmosphere has been increasing due to burning fossil fuels  Increases in Carbon Dioxide is believed to be directly proportional to increase in energy absorption by the atmosphere and increase in global temperature.

31.  Temperature Variations  Temperature of the atmosphere depends on  Latitude  Affects the angle the sun’s rays strike an area  Energy that reaches the equator is at 90° angle and is more intense than at lower latitudes  Surface features  Determines the amount of energy absorbed, reflected and reradiated.  Time of year and day  Tilt of the Earth’s axis determines seasons as the hemisphere tilted toward the sun receives direct, more intense energy from the sun

33.  Water Vapor in the Air and Surface absorbs and holds energy  Water has high specific heat. It requires a lot of energy to increase its temperature, but will take a long time to cool down.  Areas having less water vapor, such as deserts, tend to warm during the day but cool very quickly at night.  Areas with high quantities of water vapor, such as near large bodies of water, generally have more moderate temperatures as the water vapor absorbs and holds the sun’s energy.

34.  Conduction  Transfer by direct contact  Lowest few centimeters of the atmosphere are heated by conduction  Convection  Transfer within a liquid or a gas  Less dense gas or liquid rises, more dense sinks creating convection currents.  Creates ocean currents and wind Transfer of Energy

35.  Pressure differences in the atmosphere cause the movement of air  Air near the surface generally flows from the high-pressure, cold, poles toward the lower- pressure, warm, equator.  Coriolis Effect - the tendency of a moving object to follow a curved path rather than a straight path because of the Earth’s rotation.  Northern Hemisphere – currents curve to the right, or clockwise  Southern Hemisphere – currents curve to the left, or counterclockwise Atmospheric Circulation

36.  Coriolis Effect

37.  Global Winds  Convection cells - 3 looping patterns of air flow in each hemisphere create wind belts, also known as prevailing winds Trade Winds – flow toward the equator Westerlies – flow in the mid-latitudes Polar Easterlies

38.  Wind and Pressure Shifts  As the sun’s rays shift during changing seasons, the position of pressure belts and wind belts shift.  Example: The westerlies prevail in Southern Florida during the winter, but trade winds dominate in the summer.  Jet Streams  Narrow bands of high-speed winds that blow in the upper troposphere and lower stratosphere  Sometimes 100km wide and 2 to 3 km thick reaching speeds of 500km/h  Affect airline routes and storm paths

39.  Local Winds  Influenced by local temperature variations  Gentle winds that extend over less than 100km.  Land Sea Breezes  Land surfaces heat up faster than water surfaces. Air over land warms, rises, and cool air over water moves in to replace it.  Reverses at night as land surfaces cool faster than water.  Mountain and Valley Breezes  Warm air from the valley moves upward during the day  At night, cool air descends from the mountain peaks and settles in the valley

40. Chaper 23

41. Chapter 23 Changing Forms of Water  Water in the atmosphere exists in three states, or phases.  One phase is known as a gas called water vapor.  The other two phases of water are the solid phase known as ice and the liquid phase known as water.  Water changes from one phase to another when heat energy is absorbed or released.

42. Chapter 23 Changing Forms of Water, cont. Latent Heat latent heat the heat energy that is absorbed or released by a substance during a phase change  When liquid water evaporates, the water absorbs energy from the environment.  When water vapor changes back into a liquid through the process of condensation, energy is released into the surrounding air and the molecules move closer together.

43. Chapter 23 Changing Forms of Water, cont. Evaporation  Most water enters the atmosphere through evaporation of ocean water near the equator.  However, water vapor also enters the atmosphere by evaporation from lakes, ponds, streams, and soil.  Plants release water into the atmosphere in a process called transpiration.  Volcanoes and burning fuels also release small amounts of water vapor into the atmosphere.

44. Chapter 23 Changing Forms of Water, cont. Sublimation sublimation the process in which a solid changes directly into a gas (the terms is sometimes used for the reverse process)  Ice commonly changes into a liquid before changing into a gas.  When the air is dry and the temperature is below freezing, ice and snow may sublimate into water vapor.

45. Chapter 23 Changing Forms of Water, cont. The diagram below shows the different phases of water.

46. Chapter 23 Humidity  Water vapor in the atmosphere is known as humidity.  Humidity is controlled by rates of condensation and evaporation.  When the rate of evaporation and the rate of condensation are in equilibrium, the air is said to be “saturated.”

47. Chapter 23 Humidity, continued  The rate of evaporation is determined by the temperature of the air.  The higher the temperature is, the higher the rate of evaporation is.  The rate of condensation is determined by vapor pressure.  When vapor pressure is high, the condensation rate is high.

48. Chapter 23 Humidity, continued Absolute Humidity absolute humidity the mass of water vapor per unit volume of air that contains the water vapor, usually expressed as grams of water vapor per cubic meter of air

49. Chapter 23 Humidity, continued Absolute Humidity, continued  However, as air moves, its volume changes as a result of temperature and pressure changes.  Therefore, meteorologists prefer to describe humidity by using the mixing ratio of air.  The mixing ratio of air is the mass of water vapor in a unit of air relative to the mass of the dry air.

50. Chapter 23 Humidity, continued The diagram below shows the effects of vapor pressure.

51. Chapter 23 Humidity, continued Relative Humidity relative humidity the ratio of the amount of water vapor in the air to the amount of water vapor needed to reach saturation at a given temperature  If the temperature does not change, the relative humidity will increase if moisture enters the air.  Relative humidity can also increase if the moisture in the air remains constant but the temperature decreases.

52. Chapter 23 Measuring Humidity, continued Using Psychrometers to Measure Humidity  It consists of two identical thermometers. The bulb of one thermometer is covered with a damp wick, while the bulb of the other thermometer remains dry.  When the psychrometer is held by a handle and whirled through the air, the air circulates around both thermometers.  The difference between the dry-bulb temperature and the wet-bulb temperature is used to calculate relative humidity.

54. Changing Forms of Water, cont. Dew point at constant pressure and water vapor content, the temperature at which the rate of condensation equals the rate of evaporation

55. Chapter 23 Humidity, continued Reaching the Dew Point  When the air is nearly saturated with a relative humidity of almost 100%, only a small temperature drop is needed for air to reach its dew point.  Air may cool to its dew point by conduction when the air is in contact with a cold surface.  The resulting form of condensation is called dew.

56. Chapter 23 Humidity, continued Reaching the Dew Point, continued  If dew point falls below the freezing temperature of water, water vapor may change directly into solid ice crystals, or frost.  Because frost forms when water vapor turns directly into ice, frost is not frozen dew.  Frozen dew is relatively uncommon. Unlike frost, frozen dew forms as clear beads of ice.

57.  How Do Clouds Stay Up?  https://www.youtube.com/watch?v=DjByja9ejTQ https://www.youtube.com/watch?v=DjByja9ejTQ  Clouds and Weather (3:21)  https://www.youtube.com/watch?v=hJ6aeSv8xIU https://www.youtube.com/watch?v=hJ6aeSv8xIU  Types of Clouds 5:05  https://www.youtube.com/watch?v=FMagDRCpJ14 https://www.youtube.com/watch?v=FMagDRCpJ14  Clouds and Weather 3:21  https://www.youtube.com/watch?v=hJ6aeSv8xIU https://www.youtube.com/watch?v=hJ6aeSv8xIU  Rare Cloud Formations 3:05  https://www.youtube.com/watch?v=wiFyg0i9K3M https://www.youtube.com/watch?v=wiFyg0i9K3M

58. Chapter 23 Cloud Formation cloud a collection of small water droplets or ice crystals suspended in the air, which forms when the air is cooled and condensation occurs  For water vapor to condense and form a cloud, a solid surface on which condensation can take place must be available.  In addition, for clouds to form, the rate of evaporation must initially be in equilibrium with the rate of condensation.

59. Chapter 23 Cloud Formation, continued condensation nucleus a solid particle in the atmosphere that provides the surface on which water vapor condenses  Although the lowest layer of the atmosphere, the troposphere, does not contain any large solid surfaces, it contains millions of suspended particles of ice, salt, dust, and other materials.  Because the particles are so small—less than 0.001 mm in diameter—they remain suspended in the atmosphere for a long time.

60. Chapter 23 Cloud Formation, continued The diagram below shows the molecular formation of a water droplet.

61. Chapter 23 Adiabatic Cooling adiabatic cooling the process by which the temperature of an air mass decreases as the air mass rises and expands  As a mass of air rises, the surrounding atmospheric pressure decreases.  Thus, fewer collisions between the molecules happen.  The resulting decrease in the amount of energy that transfers between molecules decreases the temperature of the air.

62. Chapter 23 Adiabatic Cooling, continued Adiabatic Lapse Rate  The rate at which the temperature of a parcel of air changes as the air rises or sinks is called the adiabatic lapse rate.  The adiabatic lapse rate of clear air is about – 1°C per 100 m that the air rises.  The slower rate of cooling of moist air results from the release of latent heat as the water condenses.

63. Chapter 23 Adiabatic Cooling, continued Condensation Level  When air cools to a temperature that is below the dew point, net condensation causes clouds to form.  The altitude at which this net condensation begins is called the condensation level.  The condensation level is marked by the base of the clouds.  Further condensation allows clouds to rise and expand above the condensation level.

64. Chapter 23 Mixing  Some clouds form when one body of moist air mixes with another body of moist air that has a different temperature.  The combination of the two bodies of air causes the temperature of the air to change.  This temperature change may cool the combined air to below its dew point, which results in cloud formation.

65. Chapter 23 Lifting  Air can be forced upward when a moving mass of air meets sloped terrains, such as a mountains range.  As the rising air expands and cools, clouds form.  The large cloud formations associated with storm systems also form by lifting.  These clouds form when a mass of cold, dense air enters an area and pushes a less dense mass of warmer air upward.

67. Chapter 23 Advective Cooling advective cooling the process by which the temperature of an air mass decreases as the air mass moves over a cold surface  As air moves over a surface that is colder than air is, the cold surface absorbs heat from the air and the air cools.  If the air cools below its dew point, clouds form.

68. Chapter 23 Classification of Clouds  Clouds are classified by their shape and their altitude.  The three basic cloud forms are stratus clouds, cumulus clouds, and cirrus clouds.  There are also three altitude groups: low clouds (0-2,000 m), middle clouds (2,000 to 6,000 m), and high clouds (above 6,000 m).

69. Chapter 23 Classification of Clouds, continued Stratus Clouds stratus cloud a gray cloud that has a flat uniform base and that commonly forms at very low altitudes  Stratus means “sheet-like” or “layered.”  Stratus clouds form where a layer of warm, moist air lies above a layer of cool air.  Stratus clouds cover large areas of sky and often block out the sun.

70. Stratus Clouds

71. Chapter 23 Classification of Clouds, continued Stratus Clouds, continued  The two variations of stratus clouds are known as nimbostratus and altostratus.  Unlike other stratus clouds, the dark nimbostratus clouds can cause heavy precipitation.  Altostratus clouds form at middle altitudes. They are generally thinner than the low stratus clouds and produce very little precipitation.

72. Chapter 23 Classification of Clouds, continued Cumulus Clouds cumulus cloud a low-level, billowy cloud that commonly has a top that resembles cotton balls and has a dark bottom  Cumulus means “piled” or “heaped.”  These clouds form when warm, moist air rises and cools. As the cooling reaches its dew point, the clouds form.  The flat base that is characteristic of most cumulus clouds represents the condensation level.

73. Cumulus Clouds

74. Chapter 23 Classification of Clouds, continued Cumulus Clouds, continued  High, dark storm clouds known as cumulonimbus clouds, or thunderheads, are often accompanied by rain, lightning, and thunder.  If the base of cumulus clouds begins at middle altitudes, the clouds are called altocumulus clouds.  Low clouds that are a combination of stratus and cumulus clouds are called stratocumulus clouds.

75. Chapter 23 Classification of Clouds, continued Cirrus Clouds cirrus cloud a feathery cloud that is composed of ice crystals and that has the highest altitude of any cloud in the sky  Cirro– and cirrus mean “curly.”  Cirrus clouds form at altitudes above 6,000 m. These clouds are made of ice crystals because the temperatures are low at such high altitudes.  Because these clouds are thin, light can easily pass through them

76. Cirrus Clouds

77. Chapter 23 Classification of Clouds, continued Cirrus Clouds, continued  Cirrocumulus clouds are rare, high-altitude, billowy clouds composed entirely of ice crystals. Cirrocumulus clouds commonly appear just before a snowfall or a rain fall.  Long, thin clouds called cirrostratus clouds form a high, transparent veil across the sky.  A halo may appear around the sun or moon when either is viewed through a cirrostratus cloud.

78. Chapter 23 Classification of Clouds, continued The diagram below shows the different types of clouds in the atmosphere.

79. Chapter 23 Fog fog water vapor that has condensed very near the surface of Earth because air close to the ground has cooled  The obvious difference between fog and clouds is that fog is very near the surface of Earth.  However, fog also differs from clouds because of how fog forms.

80. Chapter 23 Fog, continued Radiation Fog  One type of fog forms from the nightly cooling of Earth.  The layer of air in contact with the ground becomes chilled to below the dew point, and the water vapor in that layer condenses into droplets.  This type of fog is called radiation fog because it results from the loss of heat by radiation.

81. Chapter 23 Fog, continued Other Types of Fog  Another type of fog, advection fog, forms when warm, moist air moves across a cold surface. Advection fog is common along coasts, where warm, moist air from above the water moves in over a cooler land surface.  An upslope fog forms by the lifting and cooling of air as air rises along land slopes.  Steam fog is a shallow layer of fog that forms when cool air moves over an inland warm body of water, such as a river.

82. Chapter 23 Precipitation precipitation any form of water that falls to Earth’s surface from the clouds; includes rain, snow, sleet, and hail  The four major types of precipitation are rain, snow, sleet, and hail.

83. Chapter 23 Forms of Precipitation  Rain is a liquid precipitation.  If the raindrops are smaller than 0.5 mm, the rain is called drizzle.  The most common form of solid precipitation is snow, which consists of ice particles.  These particles may fall as small pellets, as individual crystals, or as crystals that combine to form snowflakes.

84. Chapter 23 Forms of Precipitation, continued  When rain falls through a layer of freezing air near the ground, clear ice pellets, called sleet, can form.  In some cases, the rain does not freeze until it strikes a surface near the ground. There, it forms a thick layer of ice called glaze ice.  Hail is a solid precipitation in the form of lumps of ice. Hail usually forms in cumulonimbus clouds.

85. Chapter 23 Causes of Precipitation  Most cloud droplets have a diameter of about 20 micrometers, which is smaller than the period at the end of this sentence.  A droplet must increase in diameter by about 100 times to fall as precipitation.  Two natural processes cause cloud droplets to grow large enough to fall as precipitation: coalescence and supercooling.

86. Chapter 23 Causes of Precipitation, continued coalescence the formation of large droplets by the combination of smaller droplets  Larger droplets fall much faster through the air than small ones do.  As these large droplets drift downward, they collide and combine with smaller droplets.  Each large droplet continues to coalesce until it contains a million times as much water as it did originally.

87. Chapter 23 Causes of Precipitation, continued supercooling a condition in which a substance is cooled below its freezing point, condensation point, or sublimation point, without going through a change of state  Supercooled water droplets cannot freeze because too few freezing nuclei on which ice can form are available.  Freezing nuclei are solid particles that are suspended in the air and that have structures similar to the crystal structure of ice.

88. Chapter 23 Causes of Precipitation, continued  Most water from the supercooled water droplets evaporates.  The water vapor then condenses on the ice crystals that have formed on the freezing nuclei.  The ice crystals rapidly increase in size until they gain enough mass to fall as snow.  If the ice crystals melt and turn into rain as they pass through air whose temperature is above freezing, they form the big raindrops that are common in summer thunderstorms.

89. Chapter 23 Measuring Precipitation Amount of Precipitation  In one type of rain gauge, rainwater passes through a funnel into a calibrated container, where the amount of rainfall can then be measured.  Snow depth is simply measured with a measuring stick.  The water content of the snow is determined by melting a measured volume of snow and by measuring the amount of water that results.

90. Chapter 23 Measuring Precipitation, continued Doppler Radar  The intensity of precipitation can be measured using Doppler radar. Doppler radar images are commonly used by meteorologists for communicating weather forecasts.  Doppler radar works by bouncing radio waves off rain or snow.  By timing how long the wave takes to return, meteorologist can detect the location, direction of movement, and intensity of precipitation.

91. Chapter 23 Weather Modification cloud seeding the process of introducing freezing nuclei or condensation nuclei into a cloud in order to cause rain to fall  In areas suffering from drought, scientists may attempt to induce precipitation through cloud seeding.

92. Chapter 23 Weather Modification, continued Methods of Cloud Seeding  One method of cloud seeding uses silver iodide crystals, which resemble ice crystals, as freezing nuclei.  Another method of cloud seeding uses powdered dry ice, which is dropped from aircraft to cool cloud droplets and cause ice crystals to form.  As ice crystals fall, they may melt to form raindrops.

93. Chapter 23 Weather Modification, continued Improving Cloud Seeding  Thus, meteorologists have concluded that cloud seeding may increase precipitation under some conditions but decrease it under others.  Eventually, cloud seeding may become a way to overcome many drought-related problems.  Cloud seeding could also help control severe storms by releasing precipitation from clouds before a storm can become too large.

94. Chapter 24

95. Air Masses  Differences in air pressure are caused by unequal heating of Earth’s surface.  The equator receives more solar energy than the poles do.  Cold air near the pole sinks and creates high- pressure centers.  Differences in air pressure at different locations on Earth create wind patterns.

96. Air Pressure  Differences in air pressure are caused by unequal heating of the Earth’s surface.  Warmer air is less dense and has a lower pressure  Colder air is more dense and has a greater pressure

97. Chapter 24 How Air Moves  Air moves from areas of high pressure to areas of low pressure. Therefore, there is a general, worldwide movement of surface air from the poles toward the equator.  Temperature and pressure differences on Earth’s surface create three wind belts in the Northern Hemisphere and three wind belts in the Southern Hemisphere.  The Coriolis effect, which occurs when winds are deflected by Earth’s rotation, also influences wind patterns.

98. Wind – moving air  Created by differences in pressure  Coriolis effect causes winds to travel in a curved path.  Winds in the Northern Hemisphere turn right  Winds in the Southern Hemisphere turn left.

99. Global Winds The diagram below shows the different wind belts on Earth. Polar easterlies 60 ° - 90 ° latitude Westerlies 30 ° -60 ° latitude Tradewinds equator to 30° latitude

100. Chapter 24 Formation of Air Masses air mass a large body of air throughout which temperature and moisture content are similar  Small air pressure differences, air remains relatively stationary.  Slow moving air takes on characteristic temperature and humidity of that region.  Air masses that form over frozen polar regions are very cold and dry.  Air masses that form over tropical oceans are warm and moist.

101. Chapter 24 Types of Air Masses  Air masses are classified according to their source regions.  Polar regions form cold air masses. Tropical areas forms warm air masses.  Air masses that form over the ocean are called maritime. Air masses that form over land are called continental.  The combination of tropical or polar air and continental or maritime air results in air masses that have distinct characteristics.

102. Chapter 24 Types of Air Masses, continued Continental Air Masses  There are two types of continental air masses: 1. continental polar (cP)  cold and dry. 2. continental tropical (cT).  warm and dry.  An air mass will eventually move into other regions because of global wind patterns.

103. Chapter 24 Types of Air Masses, continued Maritime Air Masses The two different maritime air masses 1.maritime polar (mP)  moist and cold. 2. maritime tropical (mT).  moist and warm  When these very moist masses of air travel to a new location, they commonly bring more precipitation and fog

104. Chapter 24 North American Air Mass  The four types of air masses that affect the weather of North America come from six regions.  An air mass usually brings the weather of its source region, but an air mass may change as it moves away from its source region.  For example, cold, dry air may become warm and more moist as it moves from land to the warm ocean.

105. Chapter 24 Types of Air Masses, continued The diagram below shows the four types of air mass that influence North America.

106. Chapter 24 Fronts  A cool air mass is dense and does not mix with the less-dense air of a warm air mass.  Thus, a boundary, called a front, forms between air masses.  Changes in middle-latitude weather usually take place along the various types of fronts.  Fronts do not exist in the Tropics because no air masses that have significant temperature differences exist there.

107. Chapter 24 Fronts, continued Cold Fronts cold front the front edge of a moving mass of cold air that pushes beneath a warmer air mass like a wedge  If the warm air is moist, clouds will form.

108. Chapter 24 Fronts, continued Cold Fronts, continued  Large cumulus and cumulonimbus clouds typically form along fast-moving cold fronts.  A long line of heavy thunderstorms, called a squall line, may occur in the warm, moist air just ahead of a fast-moving cold front.  A slow-moving cloud front typically produces weaker storms and lighter precipitation than a fast-moving cold front does.

109. Chapter 24 Fronts, continued Warm Fronts warm front the front edge of advancing warm air mass that replaces colder air with warmer air  The slope of a warm front is gradual.  Because of this gentle slope, clouds may extend far ahead of the surface location, or base, of the front.  A warm front generally produces precipitation over a large area and may cause violent weather.

110. Chapter 24 Fronts, continued Stationary and Occluded Fronts stationary front a front of air masses that moves either very slowly or not at all occluded front a front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass of the ground and over another air mass  Sometimes, when air masses meet, the cold moves parallel to the front, and neither air mass is displaced.

111. Weather Map of the United States Chapter 24

112. Polar Fronts and Midlatitudes Cyclones midlatitude cyclone an area of low pressure that is characterized by rotating wind that moves toward the rising air of the central low- pressure region  Over each of Earth’s polar regions is a dome of cold air that may extend as far as 60° latitude.  The boundary where this cold polar air meets the tropical air mass of the middle latitudes, especially over the ocean, is called the polar front.  Waves are the beginnings of low-pressure storm centers called midlatitude cyclones or wave cyclones.  These cyclones strongly influence weather patterns in the middle latitudes.

113. Chapter 24 Severe Weather Thunderstorms thunderstorm a usually brief, heavy storm that consists of rain, strong winds, lightning, and thunder  Form in cumulonimbus clouds  The thunderstorm dissipates as the supply of water vapor decrease.

114. Thunderstorm

115. Chapter 24 Severe Weather, continued Lightning  During a thunderstorm, clouds discharge electricity in the form of lightning.  The released electricity heats the air, and the air rapidly expands and produces a loud noise known as thunder.  For lightning to occur, the clouds must have areas that carry distinct electrical charges.

116. Lightning

117. Chapter 24 Severe Weather, continued Hurricanes hurricane a severe storm that develops over tropical oceans and whose strong winds of more than 120 km/h spiral in toward the intensely low-pressure storm center  A hurricane begins when warm, moist air over the ocean rises rapidly.  When moisture in the rising warm air condenses, a large amount of energy in the from of latent heat is released. This heat increase the force of the rising air.

118. Chapter 24 Severe Weather, continued Hurricanes, continued  A fully developed hurricane consists of a series of thick cumulonimbus cloud bands that spiral upward around the center of the storm.  The most dangerous aspect of a hurricane is a rising sea level and large waves, called a storm surge.  Every hurricane is categorized on the Safir- Simpson scale by using several factors. These factors include central pressure, wind speed, and storm surge.

119. Hurricane

120. Chapter 24 Severe Weather, continued Tornadoes tornado a destructive, rotating column of air that has very high wind speeds and that maybe visible as a funnel-shaped cloud  The smallest, most violent, and shortest-lived severe storm is a tornado.  A tornado forms when a thunderstorm meets high-altitude horizontal winds. These winds cause the rising air in the thunderstorm to rotate.

121. Chapter 24 Severe Weather, continued Tornadoes, continued  A storm cloud may develop a narrow, funnel- shaped rapidly spinning extension that reaches downward and may or may not touch the ground.  If the funnel does touch the ground, it generally moves in a wandering, haphazard path.  The destructive power of a tornado is due to mainly the speed of the winds. These winds may reach speeds of more than 400 km/h.

122. Tornado

123. Chapter 24 Measuring Lower-Atmospheric Conditions Air Temperature thermometer an instrument that measures and indicates temperature  A common type of thermometer uses a liquid— usually mercury or alcohol—sealed in a glass tube to indicate temperature.  A rise in temperature causes the liquid to expand and fill more of the tube. A drop in temperature causes the liquid to contract and fill less of the tube.

124. Chapter 24 Measuring Lower-Atmospheric Conditions, continued Air Temperature, continued  Another type of thermometer is an electrical thermometer.  As the temperature rises, the electric current that flows through the material of the electrical thermometer increases and is translated into temperature readings.

125. Thermometer

126. Chapter 24 Measuring Lower-Atmospheric Conditions, continued Air Pressure barometer an instrument that measures atmospheric pressure  Changes in air pressure affect air masses.  The approach of a front is usually indicated by a drop in air pressure.

127. Barometer

128. Chapter 24 Measuring Lower-Atmospheric Conditions, continued Wind Speed anemometer an instrument used to measure wind speed  A typical anemometer consists of small cups that are attached by spokes to a shaft that rotates freely.  The wind pushes against the cup and causes them to rotate. This rotation triggers an electrical signal that registers the wind speed in meters per second or in miles per hour.

129. Anemometer

130. Chapter 24 Measuring Lower-Atmospheric Conditions, continued Wind Direction wind vane an instrument used to determine direction of the wind  The wind vane is commonly an arrow-shaped device that turns freely on a pole as the tail catches the wind.  Wind direction may be described by using one of 16 compass directions, such as north-northeast. Wind direction also may be recorded in degrees by moving clockwise and beginning with 0° at the north.

131. Wind Vane

132. Chapter 24 Measuring Upper-Atmospheric Conditions Radiosonde radiosonde a package of instruments that is carried aloft by balloons to measure upper atmospheric conditions, including temperature, dew point, and wind velocity  The radiosonde sends measurements as radio waves to a receiver that records the information.  When the balloon reaches a very high altitude, the balloon expands and bursts, and the radiosonde parachutes back to Earth.

133. Radiosonde

134. Chapter 24 Measuring Upper-Atmospheric Conditions, continued Radar radar radio detection and ranging, a system that uses reflected radio waves to determine the velocity and location of objects  For example, large particles of water in the atmosphere reflect radar pulses.  The newest Doppler radar can indicate the precise location, movement,and extent of a storm. It can also indicate the intensity of precipitation and wind patterns within a storm.

135. Chapter 24 Measuring Upper-Atmospheric Conditions, continued Weather Satellites  Satellite images provide weather information for regions where observations cannot be made from ground.  The direction and speed of the wind at the level of the clouds can also be measured by examining a continuous sequence of cloud images.  Satellite instruments can also measure marine conditions.

136. Chapter 24 Global Weather Monitoring  Weather stations around the world exchange the weather information they have collected.  The World Meteorological Organization (WMO) sponsors a program called World Weather Watch to promote the rapid exchange of weather information.  It also offers advice on the effect of weather on natural resource and on human activities, such as farming and transportation.

137. Chapter 24 Weather Maps Weather Symbols station model a pattern of meteorological symbols that represent the weather at a particular observing station and that is recorded on a weather map  Common weather symbols describe cloud cover, wind speed, wind direction, and weather conditions, such as type of precipitation and storm activity.

138. Chapter 24 Weather Maps, continued Weather Symbols, continued  Other information included in the station model are the air temperature and the dew point.  The dew point indicates how high the humidity of the air is, or how much water is in the air.  The station model also indicates the atmospheric pressure by using a three-digit number in the upper right hand corner.

139. Chapter 24 Weather Maps, continued The diagram below shows the different weather symbols used on weather maps. Section 4 Forecasting the Weather

140. Chapter 24 Weather Maps, continued Plotting Temperature and Pressure  Lines that connect points of equal temperatures are called isotherms.  Lines that connect points of equal atmospheric pressure are called isobars.  The spacing and shape of the isobars help meteorologists interpret their observations about the speed and direction of the wind.

141. Chapter 24 Weather Maps, continued Plotting Fronts and Precipitation  Most weather maps mark the locations of fronts and areas of precipitation.  Fronts are identified by sharp changes in wind speed and direction, temperature or humidity.  Areas of precipitation are commonly marked by using colors or symbols.

142. Chapter 24 Weather Maps, continued The diagram below shows an example of a typical weather map.

143. Chapter 24 Weather Forecasts  To forecast the weather, meteorologists regularly plot to the intensity and path of weather systems on maps.  Meteorologists then study the must recent weather map and compare it with maps from previous hours.  By following the progress of weather systems, meteorologist can forecast the weather.

144. Chapter 24 Weather Forecasts, continued Weather Data  Computers models can show the possible weather conditions for several days.  Comparing models helps meteorologists better predict weather.  By using computers, scientists can manipulate data on temperature and pressure to simulate errors in measuring these data.

145. Chapter 24 Weather Forecasts, continued Severe Weather Watches and Warnings  One main goal of meteorology is to reduce the amount of destruction caused by severe weather by forecasting severe weather early.  A watch is issued when the conditions are ideal for severe weather.  A warning is given when severe weather has been spotted or is expected within 24 hours.

146. Chapter 24 Controlling the Weather  Some meteorologists are investigating methods of controlling rain, hail, and lightning.  Currently, the most researched method for producing rain has been cloud seeding.  Cloud seeding can also be used to prevent more severe precipitation.

147. Chapter 24 Controlling the Weather, continued Hurricane Control  Hurricanes have also been seeded with freezing nuclei in an effort to reduce the intensity of the storm.  During Project Stormfury, which took place from 1962 to 1983, four hurricanes were seeded, and the project had mixed results.  Scientists have, for the most part, abandoned storm and hurricane control because it is not an attainable goal with existing technology.

148. Chapter 24 Controlling the Weather, continued Lightning Control  Seeding of potential lightning storms with silver-iodide nuclei has seemed to modify the occurrence of lighting.  However, no conclusive results have been obtained.

149. Chapter 25

150. Temperature and Precipitation climate the average weather conditions in an area over a long period of time  Climates are chiefly described using average temperature and precipitation.  Another way scientists describe climate is by using the yearly temperature range, or the difference between the highest and lowest monthly averages.  The factors that have the greatest influence on both temperature and precipitation are latitude, heat absorption and release, and topography.

151. Chapter 25 Latitude Solar Energy  The higher the latitude of an area is, the smaller the angle at which the sun’s rays hit Earth is and the smaller the amount of solar energy received by the area is.  Because Earth’s axis is tilted, the angle at which the sun’s rays hit an area changes as Earth orbits the sun.

152. Chapter 25 Latitude, continued The diagram below shows the varying temperatures in the Northern Hemisphere during winter.

153. Chapter 25 Latitude, continued Global Wind Patterns  Because Earth receives different amounts of solar energy at different latitudes, belts of cool, dense air form at latitudes near the poles, while belts of warm, less dense air form near the equator.  Winds affect many weather conditions, such as precipitation, temperature, and cloud cover.  Thus, regions that have different global wind belts often have different climates.

154. Chapter 25 Latitude, continued Global Wind Patterns, continued  As seasons change, the global wind belts shift in a north or south direction.  As the wind and pressure belts shift, the belts of precipitation associated with them also shift.

155. Chapter 25 Heat Absorption and Release  Land heats faster than water and thus can reach higher temperatures in the same amount of time.  Waves, currents, and other movements continuously replace warm surface water with cooler water from the ocean depths.  In turn, the temperature of the land or ocean influences the amount of heat that the air above the land or ocean absorbs or releases.  The temperature of the air then affects the climate of the area.

156. Chapter 25 Heat Absorption and Release, continued Specific Heat and Evaporation specific heat the quantity of heat required to raise a unit mass of homogeneous material 1 K or 1°C in a specified way given constant pressure and volume  Even if not in motion, water warms more slowly than land does.  Water also releases heat energy more slowly than land does.

157. Chapter 25 Heat Absorption and Release, continued Specific Heat and Evaporation, continued  A given mass of water requires more energy than land of the same mass does to experience an increase in temperature of the same number of degrees.  The average temperature of land and water at the same latitude also vary because of differences in the loss of heat through evaporation.  Evaporation affects water surfaces much more than it affects land surfaces.

158. Chapter 25 Heat Absorption and Release, continued Ocean Currents  The temperature of ocean currents that come in contact with the air influences the amount of heat absorbed or released by the air.  If winds consistently blow toward shore, ocean currents have a strong effect on air masses over land.  For example, the combination of a warm Atlantic current and steady westerly winds gives northwestern Europe a high average temperature for its latitude.

159. Chapter 25 Heat Absorption and Release, continued El Niño Southern–Oscillation El Niño the warm-water phase of the El Niño Southern Oscillation; a periodic occurrence in the eastern Pacific Ocean in which the surface-water temperature becomes unusually warm (ENSO)  The event changes the interaction of the ocean and the atmosphere, which can change global weather patterns.  The ENSO also has a cool-water phase called La Niña, which also affects weather patterns.

160. Chapter 25 Heat Absorption and Release, continued Seasonal Winds monsoon a seasonal wind that blows toward the land in the summer, bringing heavy rains, and that blows away from the land in the winter, bringing dry weather  Temperature differences between the land and the oceans sometimes cause winds to shift seasonally in some regions. Monsoon climates, such as that in southern Asia, are caused by heating and cooling of the northern Indian peninsula.

161. Chapter 25 Topography Elevation  The surface features of the land, or topography, also influences climate.  The elevation, or height of landforms above sea level, produces distinct temperature changes.  Temperature generally decreases as elevation increases.

162. Chapter 25 Topography, continued Rain Shadows  When a moving air mass encounters a mountain range, the air mass rises, cools, and loses most of its moisture through precipitation.  As a result, the air that flows down the other side of the range is usually warm and dry. This effect is called a rain shadow.  One type of warm, dry wind that forms in this way is a the foehn (FAYN), a dry wind that flows down the slopes of the Alps.

163. Chapter 25 Climate Zone  Earth has three major types of climate zones: tropical, middle-latitude, and polar.  Each zone has distinct temperature characteristics, including a specific range of temperatures.  Each of these zones has several types of climates because the amount of precipitation within each zone varies.

164. Chapter 25 Climates of the World

165. Chapter 25 Tropical Climates tropical climate a climate characterized by high temperatures and heavy precipitation during at least part of the year; typical of equatorial regions  These climates have an average monthly temperature of at least 18°C, even during the coldest month of the year.  Within the tropical zone, there are three types of tropical climates: tropical rain forest, tropical desert, and savanna.

166. Chapter 25 Tropical Climates, continued The diagram below shows the different characteristics of tropical climates.

167. Chapter 25 Middle-Latitude Climates middle-latitude climate a climate that has a maximum average temperature of 8°C in the coldest month and a minimum average temperature of 10°C in the warmest month  There are five middle-latitude climates: marine west coast, steppe, humid continental, humid subtropical, and Mediterranean.

168. Chapter 25 Middle-Latitude Climates, continued The diagram below shows the different characteristics of middle-latitude climates.

169. Chapter 25 Polar Climates polar climate a climate that is characterized by average temperature that are near or below freezing; typical of polar regions  There are three types of polar climates: the subarctic climate, the tundra climate, and the polar icecap climate.

170. Chapter 25 Polar Climates, continued The diagram below shows the different characteristics of polar climates.

171. Chapter 25 Local Climates microclimate the climate of a small area  Microclimates are influenced by density of vegetation, by elevation, and by proximity to large bodies of water.  For example, in a city, pavement and buildings absorb and reradiate a lot of solar energy, which raises the temperature of the air above and creates a “heat island.”  In contrast, vegetation in rural areas does not reradiate as much energy, so temperatures in those areas are lower.

172. Chapter 25 Local Climates, continued Effects of Elevation  As elevation increases, temperature decreases and the climate changes.  For example, highland climate is characterized by large variation in temperatures and precipitation over short distances because of changes in elevation.  Highland climates are commonly located in mountainous regions—even in tropical areas.

173. Chapter 25 Local Climates, continued Effects of Large Bodies of Water  Large bodies of waters, such as lakes, influence local climates. The water absorbs and releases heat slower than land does.  Therefore, microclimates near large bodies of water have a smaller range of temperatures and higher annual precipitation than other locations at the same latitude.

174. Chapter 25 Studying Climate Change climatologist a scientist who gathers data to study and compare past and present climates and to predict future climate change  Climatologists use a variety of techniques to reconstruct changes in climate.

175. Chapter 25 Studying Climate Change, continued Collecting Climate Data  Today, scientists use thousands of weather stations around the world to measure recent precipitation and temperature changes.  However, when trying to learn about factors that influence climate change, scientists need to study the evidence left by past climates.

176. Chapter 25 Studying Climate Change, continued Modeling Climates  Currently, scientists use computers to create models to study climate. The models incorporate millions of pieces of data and help sort the complex sets of variables that influence climate.  These models are called general circulation models, or GCMs.  Climate models predict many factors of climate, including temperature, precipitation, wind patterns, and sea-level changes.

177. Chapter 25 Potential Causes of Climate Change  By studying computer-generated climate models, scientists have determined several potential causes of climate change.  Factors that might cause climate change include the movement of tectonic plates, changes in the Earth’s orbit, human activity, and atmospheric changes.

178. Chapter 25 Potential Causes of Climate Change, continued Plate Tectonics  The movement of continents over millions of years caused by tectonic plate motion may affect climate change.  The changing position of the continents changes wind flow and ocean currents around the globe.  These changes affect the temperature and precipitation patterns of the continents and oceans.

179. Chapter 25 Potential Causes of Climate Change, continued Orbital Changes  Changes in the shape of Earth’s orbit, changes in Earth’s tile, and the wobble of Earth on its axis can lead to climate changes.  The combination of these factors is described by the Milankovitch theory.  Each change of motion has a different effect on climate.

180. Chapter 25 Potential Causes of Climate Change, continued

181. Chapter 25 Potential Causes of Climate Change, continued Human Activity  Pollution from transportation and industry releases carbon dioxide, CO 2, into the atmosphere.  Increases in CO 2 concentration may lead to global warming, an increase in temperatures around the Earth  Because vegetation uses CO 2 to make food, deforestation also affects one of the natural ways of removing CO 2 from the atmosphere.

182. Chapter 25 Potential Causes of Climate Change, continued Volcanic Activity  Large volcanic eruptions can influence climates around the world.  Sulfur and ash from eruptions can decrease temperatures by reflecting sunlight back into space.  These changes last from a few weeks to several years and depend on the strength and duration of the eruption.

183. Chapter 25 Potential Impacts of Climate Change  Earth’s atmosphere, oceans, and land are all connected, and each influences both local and global climates.  Even short-term changes in the climate may lead to long-lasting effects that may make the survival of life on Earth more difficult for both humans and other species.  Some of these potential climate changes include global warming, sea-level changes, and changes in precipitation.

184. Chapter 25 Potential Impacts of Climate Change, continued Global Warming global warming a gradual increase in the average global temperature that is due to a higher concentration of gases such as carbon dioxide in the atmosphere  Global temperatures have increased approximately 1°C over the last 100 year.  Researchers are trying to determine if this increase is a natural variation or the result of human activities, such as deforestation and pollution.

185. Chapter 25 Potential Impacts of Climate Change, continued Global Warming, continued  An increase in global temperature can lead to an increase in evaporation.  An increase in global temperatures could also cause ice at the poles to melt.  If a significant amount of ice melts, sea levels around the world could rise.

186. Chapter 25 Potential Impacts of Climate Change, continued Sea-Level Changes  An increase of only a few degrees worldwide could melt the polar icecaps and raise sea level by adding water to the oceans.  Many coastal inhabitants would be displaced, and freshwater and agricultural land resources will be diminished with the change in sea level.

187. Chapter 25 What Humans Can Do  Many countries are working together to reduce the potential effects of global warming.  Treaties and laws have been passed to reduce pollution.  Even community projects to reform areas have been developed on a local level.

188. Chapter 25 What Humans Can Do, continued Individual Efforts  Pollution is caused mostly by the burning of fossil fuels, such as running automobiles and using electricity.  Therefore, humans can have a significant effect on pollution rates by turning lights off when they are not in use, by turning down the heat in winter, and by reducing air conditioner use in the summer.

189. Chapter 25 What Humans Can Do, continued Transportation Solutions  Using public transportation and driving fuel- efficient vehicles help release less CO 2 into the atmosphere.  All vehicles burn fuel more efficiently when they are properly tuned and the tires are properly inflated.  Car manufacturers have been developing cars that are more fuel efficient. For example, hybrid cars use both electricity and gasoline.