CHAPTER 2
Weather and Climate
Weather and Climate starts with the roles of solar radiation and movements of Earth in
determining patterns of weather and climate. Following an explanation of heat storage, transfer,
and exchange is a discussion of the causes of different types of precipitation. Circulation patterns
related to atmospheric pressure variations emphasizing the four zones of global circulation,
seasonal variations, effects on ocean currents, and regional storms are covered next.
Then the role of temperature and precipitation in describing climate is explained. The
classification and description of Earth’s many important climate regions precede a concluding
section on climate change emphasizing causes and consequences of global warming.
Climates in Urban Areas is the subject of a Connections box. A Global and Local box discusses
El Niño/La Niña, whereas a Rapid Change box examines the 2007 IPCC Assessment of Global
Warming and Its Impacts.
After carefully studying this chapter, students should have an understanding of the following:
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Difference between weather and climate.
How solar radiation creates atmospheric patterns.
Earth’s rotation and orbit and their role in atmospheric patterns.
Equinoxes and solstices.
Processes of heat storage and transfer.
Convectional, orographic, and frontal precipitation.
Coriolis effect.
Four zones of global atmospheric circulation.
Global circulation patterns in January compared to July.
Various kinds of storms and severe weather.
The use of temperature and precipitation information to classify climates.
Major climate types and their global locations.
Information shown on a climograph.
Climate change.
The concept of tipping points (thresholds) and global warming.
Major Changes from the 4th Edition
All statistics updated. Increased discussion of global warming, especially the IPCC
conclusions and recent evidence of climate change.
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Chapter 2
Chapter Review
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Energy and Weather
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Solar energy drives atmospheric processes creating patterns of weather and climate.
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Earth’s orbit around the Sun, tilt, and rotation affect the insolation or amount of solar
energy at a particular location. The angle at which the Sun’s rays strikes Earth’s
surface is the angle of incidence. The more perpendicular the angle of incidence the
more solar energy received. The number of hours a day of sunlight depends on
latitude and season. Places tilted toward the Sun have more hours of sunlight. There
are always 12 hours of daylight and 12 hours of night at the equator.
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Water stores more heat than land. Land temperatures are more changeable and
extreme.
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Solar energy is radiant energy. Radiant energy is energy transmitted by
electromagnetic waves. Most insolation is shortwave radiation where successive
waves are close together, whereas most of the energy reradiated back into space is
longwave. The atmosphere contains greenhouse gases that allow shortwave to reach
the surface, but block a portion of the outgoing longwave.
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Latent heat is heat stored in the different states of water and is often responsible for
large transfers of energy.
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Convection occurs when part of a fluid is heated. Heated air will rise and cooled air
will descend. Rising or descending air causes advection, the horizontal movement of
air. Differences in insolation cause differences in heating and cooling which in turn
produce many of the basic patterns of the atmosphere.
Precipitation
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Humans expect precipitation amounts to be normal. Droughts, floods, and other
problems occur when precipitation is not what is expected.
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Precipitation occurs when there is enough condensation around tiny particles in
clouds. Condensation occurs when the pressure of moisture in the air exceeds
saturation.
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There are three ways precipitation develops. Convectional has humid air heated
near the surface, rising, being cooled adiabatically, latent heat being released,
more rising, more cooling, and ultimately precipitation often in a thunderstorm.
Orographic is caused when air is pushed upward over mountains. Cooling leads to
condensation and precipitation, especially on the windward side. The leeward side has
a rain shadow. Frontal is when warm air rises over cool air when air masses meet.
Again the warm air is cooled and precipitation results.
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Circulation Patterns
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Atmospheric pressure reflects the weight of the atmosphere’s air above a given point.
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The Coriolis effect is the deflection of air due to the rotation of Earth. Deflection to
the right or clockwise exists in the Northern Hemisphere. The opposite is true for the
Southern Hemisphere.
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Global scale convection creates the intertropical convergence zone, subtropical high
pressure zones, midlatitude low pressure zones, polar high pressure zones, trade
winds, westerlies, and polar easterlies. For example in the polar regions, cold causes
dense air, high pressure, and outward (toward the equator) moving winds that are
deflected by the Coriolis effect.
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The tilt of Earth causes seasonal shifts in the above zones and the winds. January and
July can be compared. The monsoon circulation of South Asia has winter high
pressure over Asia creating land to sea winds that allow little rain and summer low
pressure over Asia yielding sea to land winds that produce much rain (the monsoon).
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Winds and differences in water temperature and in salinity produce ocean currents
and ocean circulation patterns. For example, the Gulf Stream moves northward along
the east coast of North America bringing heat into the north Atlantic. When El Niño
occurs, weather patterns change.
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Hurricanes, midlatitude cyclones, and tornadoes are storms that start as low pressure
centers with rising air. Hurricane-induced storm surges are often very devastating.
Climate
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Climate is the summary of weather conditions over many years. Climate affects the
vegetation, natural resources, and human activities of an area. Climate changes over
time due to natural processes and human actions.
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Air temperature and precipitation are the two most important aspects of climate. Both
vary over time and location in response to many factors like insolation, elevation, and
movements of air masses. Humans need to adapt to variations in temperature and
precipitation.
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Water availability in an area is also affected by transpiration by plants.
Classifying Climate
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Climates are classified using temperature, precipitation, and vegetation information.
The Köppen scheme with five basic climates and letter codes is most commonly used.
Chapter 2
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Earth’s Climate Regions
· Humid tropical, seasonally humid tropical, desert, semiarid, humid subtropical,
marine west coast, Mediterranean, humid continental, subarctic, tundra, and ice-cap
are the eleven principal climates that are described.
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A climograph is provided for a representative location for each type of climate.
Climate Change
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Climate changes in response to temperature change over geologic time. The
Quaternary Period has had relatively many periods of warmer temperatures
followed by colder ones. The last period of colder temperatures and glaciation
peaked about 18,000 years ago.
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Astronomy and geology offer possible natural reasons for climate change.
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Humans contribute to climate change by altering the atmosphere and removing
vegetation. Humans are adding to global warming with the burning of fossil fuels
and this warming could cause sea level to rise and some areas to become drier.
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Consensus exists that Earth is warming, but there is much uncertainty concerning
details and logical responses. The IPCC is viewed as a suitable source for information.
Slowing global warming is expensive and it might be more cost effective to adapt
to climate change.
Chapter Outline
I. Introduction
A. Weather is the day-to-day changes
B. Climate is the statistical summary of weather over time
II. Energy and weather
A. Solar energy
1. Drives atmospheric processes
2. Derived from thermonuclear reactions in the Sun
B. Amount of incoming solar radiation varies
1. Earth’s orbit and tilt
a. Time of day
b. Latitude
c. Season
2. Amount intercepted at a given location
a. Angle of incidence
b. Day length
c. Distance from the Sun
3. Equinoxes (March and September) and solstices (June and December)
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C. Storage of heat
1. Water stores large amounts
2. Land stores small amounts
3. Land temperature changes faster than water temperature
D. Heat transfer between the atmosphere and Earth
1. Radiation
a. Radiant energy is transmitted by electromagnetic waves
b. Most incoming solar radiation is shortwave
c. Most outgoing energy is longwave
d. Most shortwave passes through the atmosphere
e. Some longwave is trapped by greenhouse gases
2. Latent heat
a. Heat stored in water and water vapor
b. Transfers large amounts of energy
E. Heat exchange and atmospheric circulation
1. Convection
a. Movement in any fluid when part of the fluid is heated
b. Warm air (and water) rises
2. Advection
a. Horizontal movement of air
b. Moves large amounts of air and latent heat
III. Precipitation
A. Variations in precipitation affect human activities
B. Condensation
1. Water from vapor to liquid
2. Relative humidity
3. Leads to precipitation
a. When the pressure of moisture exceeds the saturation vapor pressure
b. When clouds contain tiny particles (condensation nuclei)
C. Causes
1. Convection
a. Rising air leading to adiabatic cooling
b. Clouds form and condensation occurs
c. Thunderstorms with gusty winds and intense rain develop
d. Major cause of precipitation
2. Orographic precipitation
a. Mountains force air upward
b. Cooling, clouds, condensation, precipitation
c. Windward side has precipitation
d. Leeward side is rain shadow with less precipitation
3. Frontal uplift
a. Cold air mass pushes under a warm air mass
b. Warm air rises
c. Cooling, clouds, condensation, precipitation
d. Cold fronts and warm fronts
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Chapter 2
IV. Circulation patterns
A. Fundamental causes
1. Atmospheric pressure
a. Weight of air above a location
b. Varies with altitude
2. Coriolis effect
B. Global atmospheric circulation
1. Intertropical convergence zone (ITCZ)
a. Much solar radiation causes air to rise, creating low pressure and rain
b. Creates the trade winds
c. Pushes warm, dry air toward the midlatitudes
2. Subtropical high-pressure zones
a. Air descends, causing high pressure
b. Creates arid climate
3. Midlatitude low-pressure zones
a. Convergence of warm air and polar air
b. Causes the westerlies
4. Polar high pressure zones
a. Cold causes high pressure
b. Very little moisture
C. Seasonal variations
1. January
a. ITCZ is a few degrees south of the equator
b. Pattern of the other zones is more consistent in the Southern Hemisphere
2. July
a. ITCZ is north of the equator
b. Low pressure over Asia causing the monsoon circulation
D. Global ocean circulation
1. Winds as well as differences in seawater temperature and salinity cause currents
2. Currents form circular patterns (gyres)
a. Warm water moved toward the poles
b. Cold water moved toward the equator
E. Storms
1. Vary from huge monsoons to local thunderstorms
2. Modified by El Niño/La Niña
3. Tropical cyclone (hurricane or typhoon or cyclone)
a. Intense low pressure
b. Strong winds, much rain, and storm surges
c. Weakens over land
4. Midlatitude cyclone
a. Low pressure along polar fronts
b. Weaker than tropical cyclones
c. Sometimes leads to tornadoes
V. Climate
A. Summary of weather conditions over many years
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B. Two main components
1. Temperature
a. Varies over time and space
b. Affected by elevation and topography
2. Precipitation
a. Varies over time and space
b. Transpiration and potential evapotranspiration
VI. Classifying climate
A. Uses patterns of temperature and precipitation as related to water availability for
vegetation
B. Köppen system
a. Most recognized system
b. Used distribution of vegetation to reflect temperature and precipitation
c. Uses A, B, C, D, E to identify five main types
VII. Earth’s climate regions
A. Humid low-latitude tropical climates
1. Humid tropical (Af, Am)
a. Beneath the ITCZ
b. Warm, humid, rainy
c. Little seasonal variation
d. Tropical rainforests
2. Seasonally humid tropical (Aw)
a. Has a distinct dry season
b. Often caused by shifts in the ITCZ
c. Sometimes caused by the monsoon circulation
d. Less plant growth during dry season
B. Dry climates
1. Desert (BWh, BWk)
a. Beneath subtropical high-pressure zones
b. Very dry, especially on western sides of continents, high temperatures
c. Little vegetation
2. Semiarid (BSh, BSk)
a. More rainfall
b. Between deserts and humid regions
c. Steppes or grasslands
C. Warm midlatitude climates
1. Humid subtropical (Cfa, Cw)
a. Beneath subtropical high-pressure zones, especially on eastern sides of continents
b. More seasonal variations
c. Mostly deciduous vegetation
2. Marine west coast (Cfb, Cfc)
a. On west coasts
b. Moderate temperatures
c. Plentiful precipitation, drizzle
d. Mostly evergreen vegetation
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Chapter 2
3. Mediterranean (Cs)
a. Dry summers
b. Cool, rainy winters
c. Vegetation has to survive dry period
D. Cold midlatitude climates
1. Humid continental (Dfa, Dwa, Dfb, Dwb)
a. Only in Northern Hemisphere
b. Warm summers
c. Cold winters
d. Deciduous and some evergreen vegetation
2. Subarctic (Dfc, Dwc, Dfd, Dwd)
a. Very cold winters
b. Modest precipitation
c. Conifers (boreal forest)
E. Polar climates
1. Tundra (ET)
a. Cold throughout the year
b. Permafrost
c. Treeless tundra vegetation
2. Ice-cap (EF)
a. Very cold, quite dry
b. No vegetation
F. Climographs quantitatively describe different climates
VIII. Climate change
A. Long-run changes in the underlying determinants of climate cause climate change
B. Over geologic time
1. Glacial periods during the Pleistocene Epoch
a. Shifts in temperature back and forth
b. Most recent colder episode was about 18,000 years ago
2. Little Ice Age from 1500 to 1750
C. Causes
1. Astronomical hypotheses
2. Geologic hypotheses
3. Human activities
a. Changing the atmosphere
b. Removing vegetation
D. Global warming
1. Consensus that it is truly occurring
2. Caused by increased carbon dioxide
3. Analyses by the Intergovernmental Panel on Climate Change
4. Consequences
a. Sea-level rise
b. New patterns of precipitation
5. Uncertainties
a. Limited understanding of the climate system
b. Tipping points being reached leading to rapid change
c. Unknown future conditions
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6. Controversies over how to respond to global warming
a. Adapt to climate change
b. Reduce carbon emissions
c. Store carbon
d. “Geoengineer” the global carbon cycle, the atmosphere
Possible Questions and Topics for Discussions and Exams
1. Describe what climographs show and do not show.
2. Explain how the trade winds, westerlies, and polar easterlies are formed.
3. What is the name and Köppen code for the climate where your college is located? What are
its characteristics? Explain what causes those characteristics.
4. Compare and contrast the characteristics of hurricanes and tornadoes.
5. Look up the worst natural disasters in human history. How many were caused by weather
extremes? Using a world map, locate these disasters. Explain reasons for any patterns.
6. Compare the patterns of average January temperatures in Australia and North America.
7. Looking at Figure 2-33, which of the eleven climates covers the most area? Which covers
the least area?
8. Find climate data for your favorite foreign vacation destination. When would be the best
and worst times of the year to visit? Why?
9. Using Weatherbase.com, look up Dhaka, Bangladesh. Describe Dhaka’s temperature and
precipitation variations throughout the year.
10. Suggest reasons why weather forecasts are often inaccurate.
11. Describe the best weather for sailing, playing soccer, and sleeping. Do all students agree?
Answers to Questions for Review and Discussion
1. Using Figure 2.6 and a latitude of 40 degrees, minimum solar radiation occurs at the winter
solstice and maximum amounts at the summer solstice. As the angle of incidence becomes
less perpendicular, the intensity of solar radiation also declines. More hours of daylight
mean more solar radiation. The angle of incidence and day length do not vary by latitude at
the time of the equinoxes.
2. Radiation or the energy transmitted by electromagnetic waves, movement of water and
water vapor containing latent heat, convection or the movement in any fluid when part of
the fluid is heated, and advection or horizontal movement of air are the major processes.
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Chapter 2
3. Hurricanes occur mostly over oceans and during the late summer and fall because these
storms depend on large amounts of warm, moist air. Oceans add moisture and ocean
temperatures are the warmest in the late summer and into fall.
4. In comparison to continental interiors, climatic conditions are usually more moderate in
coastal areas. The nearby body of water slows the heating or cooling of the coastal lands.
Similarly, the continental interiors are less moderate, meaning that annual temperature
variations are greater.
5. Midlatitude cyclones occur in the midlatitudes and are centers of low pressure that develop
along a polar front. Midlatitude cyclones are more common and weaker than most
hurricanes. The passage of a front associated with a midlatitude cyclone normally causes
changes in temperatures, precipitation, and winds. In some cases, these storms become
tornadoes.
6. Related to the fact that warm air holds more moisture than cold air, higher temperatures
mean more rainfall is needed for the place to be classified as having a humid climate.
7. Humid tropical – the ITCZ is there all the time.
Seasonally humid tropical – the ITCZ shifts away during part of the year and for Asia the
monsoon circulation applies.
Desert – located in subtropical high-pressure zones, especially in western parts of
continents where high-pressure zones over adjacent oceans make the land drier.
Semiarid – subtropical high-pressure zones are not as strong, and in some cases, mountains
block air masses containing moisture.
Humid subtropical – the subtropical high-pressure zone brings moisture to eastern sides
of continents.
Marine west coast – westerlies bring air masses to west coasts of some areas.
Mediterranean – shifts in the subtropical high-pressure and midlatitude low-pressure zones
cause dry summers and cool, wet winters.
Humid continental – seasonal contrasts between the subtropical high-pressure and the
midlatitude low-pressure zones.
Subarctic – polar edge of midlatitude low-pressure zones draws in cold air.
Tundra – polar high-pressure zone has little moisture and warmth.
Ice-cap – polar high-pressure zone is strongest.
8. Over the last 1,000 years, global temperatures were warmer in about 900, cooler with the
Little Ice Age (1500 to 1750), and warming over the last 200 years. Warmer conditions and
melting of glaciers was true between 15,000 to 5,000 years ago. Based on Figure 2-56,
there were two glacial and three interglacial periods over the last 100,000 years.
9. Earth-Sun geometry, sunspots, continental drift, volcanic eruptions, burning fossil fuels,
creation of methane, use of halocarbons, and removing vegetation are possible causes of
global warming. Consequences include sea-level rises and changes in precipitation patterns
affecting agriculture and other human activities. See IPCC assessment for more details.
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