Transcript Powerpoint Presentation Natural Disasters, 5th ed.

Chapter 9
External Energy Fuels Weather
and Climate
Lecture PowerPoint
1
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Weather Versus Climate
• Weather: short-term processes
– Tornadoes, heat waves, hurricanes, floods
• Climate: long-term processes
– Ice ages, droughts, atmosphere changes, ocean circulation shifts
Processes and Disasters Fueled by Sun
• Sun powers hydrologic cycle and (with gravity) drives
agents of erosion
• Sun heats Earth unequally
– Equatorial regions receive about 2.4 times more solar energy
than polar regions
– Earth’s spin and gravity set up circulation patterns in ocean
and atmosphere to even out heat distribution
– Circulation patterns determine weather and climate
Solar Radiation Received by Earth
• Relative amounts reflected, used
in hydrologic cycle and
converted to heat are different at
different latitudes
– Equatorial belt (38oN to
38oS) faces Sun directly, so
massive amounts of solar
radiation are absorbed
– Polar regions receive solar
radiation at low angle, so
much is reflected  net
cooling
– Excess heat at equator is
transferred through midlatitudes to polar regions
Insert new Figure 11.2 here
Figure 9.3
Solar Radiation Received by Earth
• Climatic feedback cycle in polar regions:
– Receive less solar radiation  colder
– More snow and ice forms  higher albedo
(reflectivity)
– More solar radiation reflected, less absorbed
– High albedos lower Earth’s surface temperature
Solar Radiation Received by Earth
• Greenhouse effect raises Earth’s surface temperature
– Solar radiation reaches Earth at short wavelengths
– Absorbed solar radiation raises Earth’s surface temperature
– Excess heat is re-radiated at long wavelengths and absorbed by
greenhouse gases (water vapor, CO2, methane) in atmosphere,
then radiated back down to Earth’s surface  warms Earth’s
climate
– About 95% of long wavelength re-radiated heat is trapped
• Examine greenhouse effect on Earth in Chapter 12:
– Runaway greenhouse effect in early Earth history
– Human-increased greenhouse effect of 20th, 21st centuries
Water and Heat
• Required amount of heat to raise temperature of water
(specific heat) is high
• Convection: transmission of heat in flowing water or air
• Conduction: direct transmission of heat through contact
– Beach example:
temperature of
high heat capacity
water changes
little from day to
night, but hot
beach sand (with
low heat capacity)
becomes cool at
night
Insert table 9.3
Water and Heat
• Water vapor in atmosphere: between 0 and 4% by volume
– Humidity: amount of water vapor in the air
– Saturation humidity: maximum amount of water an air mass
can hold (increases with increasing temperature)
– Relative humidity: ratio of absolute humidity to saturation
humidity
– If temperature of air mass is lowered without changing absolute
humidity, will reach 100% relative humidity because at each
lower temperature, a lower saturation humidity applies
– When relative humidity reaches 100%, excess water vapor
condenses to liquid water  temperature = dew point
Water and Heat
• Water absorbs, stores and releases huge amounts of energy
changing phases between liquid, solid and gas
• Ice melting to water absorbs 80 calories of heat per gram of water
(cal/g): latent heat
• Liquid  vapor absorbs 600 cal/g: latent heat of vaporization
• Ice  vapor absorbs 680 cal/g:
latent heat of sublimation
• Liquid  ice releases 80 cal/g:
latent heat of fusion
• Vapor  liquid releases 600
cal/g: latent heat of
condensation
• Vapor  ice releases 680
cal/g: latent heat of
deposition
Figure 9.9
Water and Heat
• Air: easily compressed, denser and denser closer to
Earth’s surface
• Flows from higher to lower pressure, upward in
atmosphere, if can overcome pull of gravity  add heat
• As heated air rises, it is under lower pressure so expands
• Expansion causes adiabatic cooling (temperature
decrease without loss of heat energy)
• Descending air is compressed and undergoes adiabatic
warming (temperature increase without gain in heat
energy)
Water and Heat
• Air undergoes about 10oC adiabatic cooling per km of
rise, 10oC adiabatic warming per km of descent (dry
adiabatic lapse rate)
• As air cools, can hold less and less water vapor 
relative humidity increases
• When relative humidity = 100% (altitude = lifting
condensation level), water vapor condenses and latent
heat is released, which slows rate of upward cooling to
about 5oC per km of rise (moist adiabatic lapse rate)
Water and Heat
Differential Heating of Land and Water
• Low heat capacity of rock  land heats up and cools
down quickly
• Winter:
– Land cools down quickly, so cool air sinks toward ground 
high-pressure region
– Ocean retains warmth, so warm, moist air rises
– Cold, dry air from land flows out over ocean
• Summer:
– Land heats up quickly, so hot, dry air rises  low pressure
– Ocean warms more slowly, so cool, moist air sinks over ocean
– Cool, moist air over ocean is drawn into land, warms over land
and rises to cool, condense and form rain  summer monsoons
Water and Heat
Figure 9.10
Layering of the Lower Atmosphere
Troposphere:
• Lowest layer of atmosphere
• 8 km at poles and 18 km at equator
• Warmer at base, colder above  instability as warm air rises and
cold air sinks, constant mixing leads to weather
Tropopause:
• Top of troposphere
Stratosphere:
• Stable configuration
of warmer air above
colder air
Figure 9.13
Atmospheric Pressure and Winds
• Air flows along the pressure gradient from areas of high
pressure to areas of low pressure
• Winds are also deflected to the right (N.H.) or left (S.H) by
the Coriolis effect
Insert Figure 9.15
NOT Available; Hand Draw
Figure 9.15
Coriolis Effect
• Velocity of rotation varies by
latitude:
– 465 m/sec at equator, 0 m/sec
at poles
• Bodies moving to different
latitudes follow curved paths
• Northern hemisphere: veer to
right-hand side
• Southern hemisphere: veer to
left-hand side
• Magnitude increases with
increasing speed of moving body
and with increasing latitude (zero
at equator)
Insert revised figure
11.15 here
Figure 9.16
Coriolis Effect
• Determines paths of ocean currents, large wind systems, hurricanes
(not water draining in sinks or toilets)
Merry-go-round analogy:
• Looking down on counter-clockwise spinning merry-goround is analogous to rotation of Earth’s northern
hemisphere viewed from North Pole
– Outside edge of merry-go-round (equator) spins much
faster than center of merry-go-round (North Pole)
– Person at center tosses ball at person on edge: person on
edge has rotated away and ball curves to right
– Opposite spin and direction for southern hemisphere
Atmospheric Pressure and Winds
Rotating Air Bodies
• Northern hemisphere:
– Rising warm air
creates low pressure
area  air flows
toward low pressure,
in counterclockwise
direction
– Sinking cold air
creates high pressure
area  air flows
away from high
pressure, in
clockwise direction
Figure 9.17
General Circulation of Atmosphere
Atmosphere transports heat: low latitudes to high latitudes
Figure 9.19
General Circulation of Atmosphere
Low Latitudes
• Solar radiation at equator powers circulation of Hadley cells
• Warm equatorial air rises at Intertropical Convergence Zone
(ITCZ), then cools and drops condensed moisture in tropics
• Cooled air spreads and sinks at 30oN and 30oS, warming
adiabatically
Figure 9.20
General Circulation of Atmosphere
Middle and High Latitudes
– Hadley cells create bands of high pressure air at 30oN
and 30oS
– Air flows away from high pressure zones
– Cold air flows over land from poles to collide at polar
front around 60oN and 60oS
– Hadley, Ferrel and polar cells  convergence at ITCZ
(rain) and polar front (regional air masses)
– Global wind pattern modified by continental masses,
mountain ranges, seasons, Coriolis effect
General Circulation of Atmosphere
Air Masses
• North America:
– Cold polar air masses,
warm tropical air masses
– Dry air masses form
over land, wet air
masses form over ocean
– Dominant air-mass
movement direction is
west to east
– Pacific Ocean air masses
have more impact than
Atlantic Ocean
Figure 9.21
General Circulation of Atmosphere
Fronts
• Sloping surface separating air masses with different temperature
and moisture content, can trigger severe weather, violent storms
• Cold front: cold air mass moves in and under warm air mass,
lifting it up (tall clouds, thunderstorms)
• Warm front: warm air flows up and
over cold air mass (widespread clouds)
Insert Figure 9.22a
Figure 9.22a
Insert Figure 9.23b
Insert Figure 9.23a
Figure 9.23b
Figure 9.23a
General Circulation of Atmosphere
Jet Streams
• Relatively narrow bands of high-velocity (around 200
km/hr) winds flowing from west to east at high altitudes
– Pressure decreases more slowly moving upward through warm
air than through cold air  warm air aloft has lower pressure
than cold air  warm air flows toward cold air (toward poles)
– Spin of Earth turns poleward air flows to high-speed jet stream
winds from the west (Coriolis effect)
– Subtropical jet:
about 30oN
– Polar jet: more
powerful, about 60oN,
changing path
Figure 9.25
General Circulation of Atmosphere
Rotating Air Bodies
• Northern hemisphere:
– Meanders in jet stream may help to create rotating air bodies
– Trough of lower pressure (concave northward bend)
• Forms core of cyclone (counterclockwise flow)
– Ridge of higher pressure (convex northward bend)
• Forms core of anticyclone (clockwise flow)
Figure 9.26
General Circulation of Atmosphere
Observed Circulation of the Atmosphere
• Significant variation of air pressure and wind patterns by
hemisphere and season
• Seasonal changes not so great in Southern Hemisphere with mostly
water surface
• Northern Hemisphere wind and heat flow directions change with
seasons
– Winter has strong high-pressure air masses of cold air over
continents
– Summer has thermal lows over continents, Pacific and Bermuda
highs
General Circulation of the Oceans
• Surface and near-surface ocean waters absorb
and store huge amounts of solar energy
• Some solar heat transferred deeper by tides and
winds
• Surface- and deep-ocean circulation transfers
heat throughout oceans, affects global climate
General Circulation of the Oceans
Surface Circulation
• Surface circulation mostly driven by winds
• Movement of top layer of water drags on lower layer, etc., moving
water to depth of about 100 m
• Wind-driven flow directions are modified by Coriolis effect and
deflection off continents
• Carries heat from low latitudes toward poles
General Circulation of the Oceans
Surface Circulation
• North Atlantic Ocean:
– Warm surface water
blown westward
from Africa into
Caribbean Sea and
Gulf of Mexico
– Westward path
blocked by
continents, forced
northward along
eastern side of
North America, east
to Europe (warms
Europe)
Figure 9.28
General Circulation of the Oceans
Deep-Ocean Circulation
• Oceans: layered bodies of water with progressively
denser layers going deeper
• Water density is increased by:
– Lower temperature
– Increased dissolved salt content
• Deep-ocean water flow is thermohaline (from heat, salt)
flow: overturning circulation
General Circulation of the Oceans
• Ocean water has higher density at
– High latitudes (lower temperature)
– Arctic and Antarctic (fresh water frozen in sea ice,
remaining water made saltier)
– Warm climates (fresh water evaporated, remaining
water made saltier)
• Densest ocean water forms in northern Atlantic Ocean and
Southern Ocean
End of Chapter 9