Introduction to Geography
People, Places, and Environment, 6e
Carl Dahlman
William H. Renwick
Chapter 2: Weather and Climate
Holly Barcus
Morehead State University
And Joe Naumann
UMSL
Weather & Climate affect us in many
ways
2
Major Factor in Habitability of Areas
• Affects human
comfort levels
• Affects the “costs” of
living and working in
an area – extremely
high cost of mineral
extraction in mineralrich Siberia
• Affects the
agricultural products
that can be produced
3
Weather and Climate
• Weather
– Day-to-day variations in temperature and
precipitation
• Climate
– Statistical summary of weather conditions
through time
– Definition: The average yearly pattern of
precipitation and temperature.
4
Weather Conditions
• Examples: storms, temperature
• Movement of “energy”
– Fundamental features of Earth’s surface
– Regulate natural systems
– Limit human use of environment
5
Weather & Climate
• Whereas climate is the average annual pattern
of precipitation and temperatures for an area,
weather is the momentary, and very temporary,
condition of the atmosphere.
• Weather is experienced moment by moment
• To experience the climate of an area, one must
live there for many years. To truly experience
climate, one must experience the extremes as
well as the averages.
6
Solar Energy
• Radiant energy from sun (insolation)
• Powers circulation of atmosphere and
oceans and supports life on Earth
• Varies across Earth’s surface
7
Insolation
• Amount of energy intercepted by Earth
• 2 factors
– Intensity of solar radiation
– Duration of sunlight
8
Intensity of Solar
Radiation
• Angle of incidence
• Varies daily & seasonally
– Axial tilt = 23.5 degrees
• Lower angle = larger area =
lesser intensity
• Higher angle = smaller area =
greater intensity
9
Earth-Sun Relationships: Click the
Stonehenge picture below to see video
• Even in
ancient times,
humans were
able to
observe that
the relationship
differed from
day to day in a
cycle.
10
Air Temperature
• Earth Inclination (23.5º tilt of the axis is
responsible for the seasons and
redistributing the heat energy received)
• Reflection and Reradiation – human actions
can affect this
• The Lapse Rate – 3.5° per 1000 feet
– Decrease with ascent
– Increase with descent
11
Latitude
• Sun is directly overhead at the equator
– March Equinox – March 20 or 21
– September Equinox – Sept. 20 or 21
• June Solstice – June 20 or 21
– Tropic of Cancer
• December Solstice
– Tropic of Capricorn
• Hemispherically Correct Terminology used above
12
Earth Inclination (tilt of axis)
• 23½° tilt from the
vertical.
• Check Tropics of
Cancer &
Capricorn
• Check Arctic &
Antarctic Circles
• Relationship or
coincidence?
13
Length of Day
• Total heat received by a place is dependent upon
the number of hours of sunlight and its intensity
(angle of inclination)
• Equator
• Higher latitudes
14
Seasonal change in insolation in the
middle latitudes
• The angle at
which the sun’s
rays strike the
earth change
from day to day
as a result of
the tilt of the
earth’s axis, not
because the
sun moves.
North of the Tropic of Cancer and south
of the Tropic of Capricorn, the rays
never strike at a right angle
(perpendicular)
15
What if the axis were perpendicular?
16
Seasonal Variation in Radiation
• Varies because of angle of incidence, day length,
distance from sun
• Equator
• High latitudes
• Temperature
17
Tilt of the Earth’s Axis -• Responsible for
changing lengths
of days
throughout the
year
• Responsible for
seasons
• Responsible for
variability of
insolation
Helps redistribute and moderate
temperatures keeping the tropics from
being even hotter and the poles colder.
18
Energy Balance
19
Solar Heat Storage
• Heat is absorbed by and released from objects
• Water absorbs and releases more heat than land
– Land heats and cools more quickly and to a greater
extent than water
– Water is a moderating influence on temperatures
20
Differential Heating of Land and
Water
21
Adiabatic Process
• Water vapor in the atmosphere affects the
heating/cooling rate of air
• Latent heat (stored in water vapor) affects
temperatures
• Latent heat exchange (transfer of heat
from lower altitudes to higher ones) is very
important in causing precipitation.
22
The Three States of Water
23
Adiabatic Process Video: click the
thermometer to see the video
• For our purposes,
we will only
consider the dry
lapse rate.
• 3.5°F increase per
1000 foot decrease.
• 3.5°F decrease per
1000 foot increase
24
Heat Transfer
• Responsible for movement of energy
from place to place on Earth
• Radiation (radiant energy)
– Electromagnetic waves
• Heat (short waves converted to long waves)
– 2 wavelengths: Short (sun - light) and long (Earth heat)
25
Greenhouse Effect
• Short vs. long waves
• Greenhouse gases
– Critical to heat exchange
– Water vapor, carbon dioxide, ozone,
methane
• Increased greenhouse gases =
increased global warming
26
Greenhouse Effect
• Click the greenhouse to see the video
27
Greenhouse effect & Global
Warming
• Click the greenhouse to see the video
28
Latent Heat Exchange
• Transfers energy from low to high latitudes
• Causes precipitation
• Two types
– Sensible
• Detectable by touch
– Latent
• “In storage” in water and water vapor
• Latent heat exchange (adiabatic process)
29
Heat Exchange & Atmospheric
Circulation
• Convection
– Upward movement of fluids caused by heating
– “Boiling water”
– Atmosphere
• Advection
– Horizontal
movement of air
– Monsoons
30
Wind Definition
• Wind is the horizontal movement of air from a high
pressure area to a low pressure area.
31
Sea Breeze
1.
2.
3.
4.
5.
6.
High Pressure
Warm air over
land rises (low)
Sea Breeze
moves inland
Cumuli develop
aloft and move
seaward
Upper level return
land breeze
Cool air aloft
sinks over water
(high)
Sea Breeze
(meso-cold) Front
Low Pressure
32
Land Breeze
1.
2.
3.
4.
5.
Low Pressure
High Pressure
Cool air over
land sinks
(high)
Land Breeze
moves out
over water
Relatively
warmer water
heats air
which then
rises (low)
Upper level
return sea
breeze
Cool air over
land sinks
33
Radiation, Heat & Migrating Tropical
Low (ITC)
•
Notice that the more intense
radiation zones move from
north of the equator to south
of the equator and back –
caused by the axis tilt
34
The Tropical Low (ITCZ) – Driving
Engine of the Wind System
• There is a
seasonal lag in
the shifting of
the wind belts.
35
Apparent shifting of direct radiation
from the sun and the resulting wind
belts
36
Hydrologic Cycle –Temperature/
Precipitation Relationship
Click this diagram to see a video
Water vapor
is
continually
changing
from a gas to
a liquid and
from a liquid
to a gas.
Where it is
cold enough,
the change
also involves
ice. 37
Precipitation
• “Normal” precipitation
• Condensation
– Conversion of water from vapor to liquid state
• ALL air holds water
– Dependent on temperature
• Saturation vapor pressure
– Maximum water vapor air can hold at a
particular temperature
38
Relative Humidity
• Water content of air
• Percent of water air could hold at a given temperature
• Fluctuates hourly as temperature changes
Temperature
Relative Humidity
86 degrees F
50% if holds half water vapor
possible
71 degrees F
75%
60 degrees F
100%
• Saturation point = condensation
• Condensation = clouds
Precipitation: 3 Types
• (1) Convectional precipitation
– Warm, humid rises, expanding and cooling
– Saturation point is reached
– Clouds form
– Adiabatic cooling
• Decrease in temperature that results from
expansion of rising air
• Convectional storms
40
(2) Orographic Precipitation
•
•
•
•
Wind forces air up and over mountains
Rain on windward side
Desert on leeward side: Rain shadow
Examples
– Cascades & Sierras
– Rockies
– Exception: Appalachians
42
(3) Frontal Precipitation
• Air forced up a boundary between cold and warm air
masses
• Air mass
– Region of air with similar characteristics
• Cold front
– Cold air mass moves towards warm air mass
– Typical weather
• Warm front
– Warm air mass moves towards cooler air mass
– Typical weather
44
Frontal (Cyclonic) Precipitation
–curving & rotation come from the Coriolis effect.
Normally, a mass of
warm air rises
above a mass of
cooler air when the
two masses meet.
As the warmer mass
cools, there is
condensation and
possibly
precipitation.
47
Cold front closes the gap
48
Circulation Patterns
• Air mass = 14.7 lbs per square inch
• Atmospheric pressure
– Varies with altitude
• Higher altitude = less atmospheric pressure
– Barometer
– Maps use isobars
49
Jet Streams
• Fluctuations in the
jet streams affect
the behavior of
various air masses.
• Their immediate
effect is on
weather.
50
Air Masses Affecting N. America
Summer
WIND BELT SHIFT
Winter
• St. Louis winter
– cyclonic
(frontal)
precipitation
• St. Louis
summer –
convectional
precipitation
51
Pressure and Winds
• Air density
– Warm air = less dense
• Pressure gradient
– Difference in pressure between two places
• Coriolis Effect
– Indirect, curving path of wind caused by rotation
of the Earth
– Strongest in polar regions
52
Click the picture to see the Flash
animation
53
Global Circulation
• 4 zones
– Intertropical convergence zone (ITCZ)
• Convectional precipitation
• Trade winds
– Subtropical high-pressure zones
• Areas of dry, bright sunshine, little precipitation
– Midlatitude low-pressure zones
• Polar front
• Westerlies
– Polar high-pressure zones
• Dense air, high pressure
• Little precipitation
• Seasonal variations
54
Wind Belts
• In April, the
belts start
shifting to the
north.
• In October, the
belts start
shifting to the
south.
55
Monsoon – a seasonal shifting of wind
direction.
• Wind: horizontal movement of air from a high to a low pressure
area
• Where? -- South, Southeast, & East Asia
56
• Southeastern U.S. (not as pronounced in the U.S.)
Our Water World
• Surface – 70% water
• Water moves horizontally, vertically, and obliquely
• Some movement results in heat transfers
– Polar waters to equatorial areas & visa versa
– Upwelling of water from depths of 200 ft. plus
– Slow descent of surface waters
• Some movement doesn’t transfer heat
– Storm activity, tidal movements, seismic waves
• Ocean currents are those movements that transfer
heat
57
Ocean Circulation Patterns
• Wind creates waves and currents
• Gyres
– Wind-driven circular flows
• El Niño
– Occasional shifts in ocean circulation
58
North Atlantic Drift Moderates
European Temperatures
Characteristics of Ocean Currents in
the three-dimensional oceans
•
•
•
•
•
•
•
Cold – a relative term
Warm – a relative term
High salinity – a relative term
Weakly saline – a relative term
Occurring at great depth
Occurring at intermediate depths
Occurring at the surface
60
Prevailing Winds Influence Ocean
Currents
• Between tropics greatest volume of water flows to the
west
– Influenced by the northeasterly trade wind belt and the
southeasterly trade wind belt [solar power?]
– Small countercurrent between them
– When the westerly currents reach continental shores – are
deflected poleward (Coriolis force)
• In the midlatitudes, the prevailing westerlies propel the
ocean currents to the east
• Result: circulating systems (gyres)
– Clockwise circulation in northern hemisphere & counterclockwise
circulation in southern one.
61
El Nino: Click the CD to see
the video
• La Nina produces the opposite effects
62
The Ocean’s Role in the Ecosystem
• Redistributes heat preventing greater extremes
at the tropics and the poles
– Poles less cold
– Tropics less hot
• Source of atmospheric humidity (evaporation)
• Home of abundant plant and animal life –
valuable food sources
• Phytoplankton produce much oxygen
63
Precipitable Water Vapor
64
Storms
• Cyclones
– Large low-pressure areas
– Winds
• Counterclockwise in Northern Hemisphere
• Clockwise in Southern Hemisphere
• Hurricanes and typhoons
– Tropical cyclones
– Need warm, moist air
• Most powerful over oceans
– Storm surge
• Elevated sea level in center of storm
• Midlatitude cyclones
65
Severe Storms: Click the picture of a
warm front to see the video
66
Climate
• Summary of weather conditions over
several decades or more
• Influences
• Changes over time
• Humans and climate
• 2 primary measures
– Temperature
– Precipitation
67
Frequently encountered
terms:
Tierra Caliente
Tierra Templada
Tierra Fria
Air
Temperature
• Variation
– Latitude
– Seasonal
solar
energy
input
– Elevation
– Topography
68
Precipitation
•
•
•
•
•
•
Variable between places and through time
Worldwide variation = 0-120 inches
Global circulation patterns
Amount of precipitation
Reliability
Regularity
– Soil saturation
– Human adjustments
69
Classifying Climate
• Allows analysis and planning
• Communication
• Köppen System
– Wladimir Köppen, 1918
– Distribution of plants
– 5 basic climate types with subdivisions
– Most widely used system
70
Climate Regions
• Horizontal bands based on latitude
• Climate regions similar to
– Bioregions/Vegetation Retions
– Temperature and precipitation maps
• Other influences (see next slide)
71
CLIMATE VARIABLES: Lamppost!
• Latitude
•
•
•
•
•
•
•
Altitude
Maritime Influence
Pressure Systems
Prevailing Winds
Ocean Currents
Storms
Topography
72
Climate System Model
73
Humid Low-Latitude Tropical
Climates (A)
• Warm all year
• Humid tropical (Af, Am)
–
–
–
–
+/- 10 degrees N/S of equator
Warm & humid; Little seasonal temp. variation
High temps; Rain
Amazon River Basin, Equatorial Africa, Islands of South
East Asia
• Seasonally humid tropical climates (Aw)
– Concentrated rainfall
• Seasonal shifts of ITCZ
– Central & South America
75
Dry Climates (B)
• Dry climates, BW & BS
– 35% of Earth’s land area
– Border low latitude humid climates on North and South
– North Africa, Central Asia
• Desert climates (BWh, BWk)
– Warm and dry
– Subtropics
– New Mexico (BWh), China (BWk)
• Semi-arid climates (BSh, BSk)
– Transitional areas between deserts and humid areas
– Grasslands, steppes
– Seasonal temperature contrasts
76
Warm Mid-latitude Climates (C)
• Seasonal temp variation (4 seasons)
– Reversed seasons in the southern hemisphere
• Less precipitation
• Humid subtropical (Cfa, Cw)
– Latitude: 25-40 degrees on east side of continents
– Eastern China, SE US, Brazil, Argentina
• Marine west coast (Cfb, Cfc)
– Continental west coasts, 35-65 degrees
– Mild climates
– California to coastal Alaska, Southern Chile
• Mediterranean climates (Cs)
– Dry summers with seasonal precipitation
77
Cold Mid-latitude Climates (D) – Only
found in the northern hemisphere
• Humid continental climates (Dfa, Dwa, Dfb, Dwb)
– Strong contrasts
– Remote from oceans = little moisture
– Interior & eastern side of Northern Hemisphere Continents (35-60
degrees)
• Subarctic climates (Dfc, Dwc, Dfd, Dwd)
–
–
–
–
Northern edge of humid continental climates
No agriculture
Northern Hemisphere only
Vegetation: Boreal forests
78
None in southern hemisphere
• St. Louis on border between Dfa & Cfa to the
south
79
Polar Climates (E)
•
•
•
•
High latitude climates
Low temps
Extreme seasonal variability
Tundra climate (ET)
– Permafrost
– Tundra
• Ice-cap climates (EF)
– Near poles & high altitudes at low latitudes
80
USA Climatically “Blessed”
• Within the 50 states and Puerto Rico, the USA
has some of every type of climate in most
classification systems (variations of Kopen
– The US can produce at least some of every type of
food and industrial crop in the world
– No other country has this distinction
• The USA has relatively large areas of climate
that have the potential to be highly productive
agriculturally
81
Climate Change: 3 hypotheses or
a combination of them
• Astronomical
– Geometry of Earth’s orbit
– Sunspots
• Geologic
– Continental drift
– Volcanic eruptions
• Human (human actions may accelerate or
exacerbate changes in the other two)
– Atmosphere – pollution & global warming
– Vegetation – massive destruction of biomes
82
Climate change is very complex.
• Inconstant Climates – historical evidence of significant
changes – dynamic, not static
• Cyclical Change – cycle of wet and dry years in the
Midwest around St. Louis
– Have we identified all the various cycles?
– More frequent El Niño years? Linked to human actions?
• Human Actions –
– Global Warming
– Great reduction of the rainforests
• Major humidity pumps for the atmosphere
• Major oxygen producers (often overlooked feature)
83
More about climate cycles
• El Niño & La Niña – period between
them may be shortening
• The “Dust Bowl” was the result of a
cycle of wet and dry years in the
Great Plains that humans did not
understand
84
Human Impact on the Arctic: Click the
map to see the video
• Global
warming
• Ozone
depletion
• Resource
extraction
• Settlement
85
Solar powered world
86
Solar-Powered World
So many things on earth depend on the sun that it
may not be an understatement to say that we
live on a solar-powered world.
1. Without the sun the earth would be frozen and
lifeless
2. Sun warms the earth to a range of temperatures
where a variety of chemical compounds exist as
solids, liquids, or gases in some places – H2O
can exist in all three.
87
More solar-powered world
3.
4.
H2O, particularly in liquid state is vital to practically
every form of life on earth
Sunlight provides the energy for photosynthesis which
produces plant food
1.
2.
5.
6.
Basis of food chain
Uses CO2 and produces O2
Solar energy results in variable heating and cooling of
the earth surface, thereby causing wind and driving
the wind belts.
Ocean currents are partly solar-powered because the
wind belts influence them.
88
More solar-powered world
7. Tilt of the earth’s axis helps distribute the
insolation over a larger parts of the earth’s
surface and causes the seasons.
8. Burning fossil fuels is merely releasing energy
that plants received from the sun and locked
into their cells long, long ago.
9. Burning wood (hasn’t had time to become a
fossil fuel) is also merely releasing energy that
plants received from the sun and locked into
their cells
89
Solar Powered World: fossil fuels
90
Interactions With Climate
Everything is interconnected
in the biosphere.
• Soil
– Decomposer activity
– Moisture content
• Vegetation – food
chain base
– Succession of plants
& climax vegetation
• Available water
– Streams & ground
water
91
Natural Vegetation
• Develops in response to soil and climate
• Influences soil by providing the organic matter or
humus – i.e. rainforest feed itself
• Influences climate
– Evapotranspiration provides much of the humidity –
the cutting down of tropical rainforests may result in
decreased precipitation and prevent the
reestablishment of rainforests
• Reaches and maintains a climax vegetation
condition as long as climate remains constant
and human actions don’t interfere.
92
Tropical Rainforest Exists on Extremely
Poor Soil
Very poor, lateritic soil
93
How “Physical” are the Physical
Factors in the Biosphere?
• The human impact on climate and other
physical systems is a serious problem!
The end of Chapter 2
94