Transcript Unit 2: Air Part 1: Atmosphere & Climate

Unit 2: Air
Part 1: Atmosphere & Climate
Thank God men cannot fly, and lay waste the sky as well as the
earth. - Henry David Thoreau
1
KEY IDEAS
► Earth
is characterized by patterns of temperatures
and precipitation.
► These patterns arise from the circulation of air and
ocean water, which is ultimately driven by unequal
heating of Earth by the Sun, the rotation of Earth,
and Earth’s geographic features.
► Geographic variations in temperature and
precipitation have led to the development of
distinct terrestrial biomes, which are defines by
their unique plant communities, and distinct
aquatic biomes.
ATMOSPHERE AND CLIMATE
► Weather
- A description of short-term
physical conditions of the atmosphere in a
local area.
 An afternoon thunderstorm
► Climate
- A description of the long-term
weather pattern in a particular area.




Temperature
Humidity
Wind
Rainfall
3
HOW DOES CLIMATE & WEATHER
AFFECT LIFE?
Regional differences in temperature and precipitation
collectively help determine which organisms can survive in
each region.
To understand these differences, we need to understand the
processes that effect the distribution of heat and
precipitation.
These processes include:
Unequal heating of Earth by the Sun
Atmospheric Convection Currents
Rotation and Revolution of Earth on Tilted Axis
Ocean Currents
The Atmosphere
► The
atmosphere is a layer of gasses
surrounding the Earth consisting of 5 layers
 If the Earth were the size of an apple, the
atmosphere would be the skin.
5
Layers of the Atmosphere
6
Layers of the Atmosphere
► Troposphere
(0 km to 16 km; 10 miles)
 Largest and lowest part of atmosphere.
 Weather occurs in this layer.
 Carbon dioxide is trapped in this layer, forming
the basis of the greenhouse effect and global
warming.
 Most dense layer; Most of the gas (Nitrogen,
Oxygen, Water Vapor) found here.
 Large amount of circulation and mixing
 Temperature decreases as altitude increases.
7
Layers of the Atmosphere
► Stratosphere
(16-50km; 10-31 miles)
 Very stable, calm layer of the atmosphere; Less
dense due to distance from Earth’s gravitational
pull.
►Used
by aircraft.
 Contains the ozone layer (Made of Ozone
molecules); Incoming UV rays reach higher
altitudes first, thus the higher altitudes are
warmer. (Temp increases as altitude increases)
A Word about Ozone (O3)
► Ozone
is a pale blue gas composed of 3
oxygen molecules.
► The layer of ozone absorbs MOST of the
Sun’s ultraviolet-B (UV-B) radiation and ALL
of its ultraviolet-C (UV-C) radiation.
 UV radiation can cause DNA damage and cancer
in organisms, so the ozone layer provides a
critical shield of protection for life on Earth.
Layers of the Atmosphere
►
►
MESOSPHERE: (~60-100 km)
THERMOSPHERE: (~100 km-600 km)
 Blocks harmful X-ray & UV radiation
 Contains charged gas molecules that, when hit by solar energy,
begin to glow and produce light
 The interaction is driven by magnetic forces at the poles.
►
EXOSPHERE
►
Due to weaker gravitational pull on molecules at these
altitudes, the pressure and density in each of these
layers decrease as it extends into space.
► Aurora
Borealis
(Northern Lights)
► Aurora
Australis
(Southern Lights)
THE EARTH & THE SUN
► The
Sun has the greatest influence on Earth
 Affects its movement
 Determines day-night and seasonal cycles
 Driving climatic systems and long term climate
cycles
 Provides energy for most life on Earth
►Also
plays part in TIDAL movement by modifying the
effect of the Moon to produce monthly variation in
the tidal range.
The Sun
► The
Sun emits various types of radiation,
most of which is absorbed by the
ATMOSPHERE.
► The radiation that reaches the surface:
 Visible Light: Critical to producers
 Infrared Radiation:
 Ultraviolet
► Intensity
of solar radiation is not uniform
around the Earth, thus….
The Earth & The Sun
► ..THE
UNEVEN HEATING EFFECT,
TOGETHER WITH THE EARTH’S ROTATION,
PRODUCE THE GLOBAL PATTERNS OF
WIND AND OCEAN CIRCULATION THAT
PROFOUNDLY INFLUENCE THE EARTH’S
CLIMATE!!
THE EARTH & THE SUN
► SOLAR
YEAR: Earth takes 365.25 days to
orbit around the Sun (Revolve)
► EARTH DAY: Earth spins (Rotation) on its
axis once every 23 hours 56 minutes 4.09
seconds)
► Earth does not spin upright; it has a 23.5
degree tilt. The tilt ALWAYS faces the SAME
way= Results in seasonal changes in
sunlight and weather.
Sun Angle Controls
Sunlight Intensity
►At low angles (Oblique), sunlight
spreads over much larger areas &
thus heats less effectively.
►At low angles, sunlight reflects from
water & ice more efficiently.
Garrison, 2005
Poleward Heat
Transport to
Balance
Unequal
Heating
►Equator
would be
hotter & poles
would be much
colder without this
transport.
►Transport by
winds & ocean
currents.
Garrison,
2005
► Visible
Solar Radiation
light is energy waves that we can see
as color.
 These pass through the atmosphere.
► Ultraviolet
light is energy waves that we
cannot see but can cause sun burns and
cancer.
 These are absorbed by ozone in the stratosphere.
► Infrared
radiation is the energy of the sun that
we feel as heat.
 This is absorbed by carbon dioxide and water in
the troposphere.
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Energy and the Greenhouse
Effect
► Solar Radiation
 Of solar energy reaching outer atmosphere:
►25%
reflected
►25% absorbed
►50% reaches earth’s surface
 Of the solar energy that reaches the surface,
much is reflected:
►Fresh
clean snow
►Dark soil
►Net average of earth
90%
3%
30%
20
EARTH’S TILT & THE SEASONS
► Because
of the 23.5 degree tilt of Earth on it’s
axis, most regions of the world experience
seasonal changes in temperature and
precipitation.
 When the Northern Hemisphere is tilted toward the Sun,
the Southern Hemisphere is tilted away from the Sun.
 The Sun’s rays strike the equator directly 2x a year: the
March equinox and the September equinox.
► On
these days, virtually all regions experience 12 hours of
daylight and 12 hours of darkness.
► For the 6 months between March and September equinoxes,
the N.H. tilts toward the Sun (more daylight hours than
darkness)
EARTH’S TILT & THE SEASONS
► On
June 20 or 21 (June Solstice), the Sun is
directly above the Tropic of Cancer (23.5 degrees
N), the N.H. experiences more daylight hours than
on any other day of the year.
► For the 6 months between September and March,
the N.H. tilts away from the Sun and experiences
fewer hours of daylight than darkness.
► On December 21 or 22 (December Solstice), the
Sun is directly over the Tropic of Capricorn (23.5
degrees South).
 On this day, the N.H. experiences its shortest daylight
period of the year.
EARTH’S TILT & THE SEASONS
► In
summary, Earth’s tilt on its axis produces
predictable seasons.
Solar Radiation
25
KEY CONCEPT
UNEQUAL HEATING OF THE EARTH
Caused by:
1.
Variation in the angel at which Sun’s rays strike Earth
►
-The tropics (near equator) hit at perpendicular angle.
-Mid-latitude and polar regions are hit at more oblique angles.
*As a result, the Sun’s rays travel a shorter distance through the
atmosphere to reach Earth’s surface in the tropics.
In other words, at high latitudes, sunlight must pass through more
atmosphere, and thus lose more of its energy.
KEY CONCEPT
►
►
UNEQUAL HEATING OF EARTH
Caused by:
2. Variation of amount of SURFACE AREA over which the
Sun’s rays are distributed.
-The perpendicular angle of rays in the tropics cause
solar energy to be distributed over a smaller surface area
there than at higher latitudes.
- Shine light on ball…you get a focused orb of light.
-Shine light on top of ball at oblique angel..you get an oval
pool of dimmer light over a larger area.
KEY CONCEPT
► UNEQUAL
HEATING OF EARTH
Caused by:
3. Certain areas of Earth reflect more solar energy
than others
*The percentage of incoming sunlight that is
reflected from a surface is called its ALBEDO
-The higher the albedo of a surface, the more
solar energy it reflects, and the less it absorbs.
-A white surface has a higher albedo than a
black surface, so it tends to stay cooler.
How Uneven Heating Drives
Circulation
► The
amount of heat in the atmosphere
directly affects the movement of water.
► Warm air containing evaporated water rises
higher into the atmosphere.
 Warm air is less dense than cool air.
► As
warm air rises, heat is released into the
atmosphere and the water vapor condenses.
 The condensed water then falls as rain or snow.
29
PROPERTIES OF AIR
►
1.
2.
3.
4.
4 Properties of Air Determine How it
Moves:
Density
Vapor Capacity
Adiabatic Heating or Cooling
Latent Heat Release
1. DENSITY OF AIR & 2. VAPOR
CAPACITY
► Less
dense air RISES, dense air SINKS…
► Warm air has a lower density than cold air
 Therefore, warm air rises
 Also, hot summer days=high humidity
► The
warm air contains a lot of water
► Saturation
Point: Max. amount of water that can
be in the air at a given temperature.
 When air temp. falls, its saturation point decreases &
water vapor condenses into liquid water, clouds form,
and precipitation occurs.
3. ADIABATIC HEATING & COOLING
► As
air rises higher in the atmosphere, the pressure
on it decreases.
 The lower pressure allows the rising air to expand in
volume, and this expansion lowers the temperature of
the air
► Called
ADIABATIC COOLING
 When air sinks towards the Earth, the pressure on it
increases. The higher pressure forces the air to
decrease in volume, and this decrease raises the
temperature of the air
► Called
ADIABATIC HEATING
4. LATENT HEAT RELEASE
► =The
production of heat when water vapor
condenses from a gas to a liquid.
► When water vapor in the atmosphere
condenses into liquid form, energy is
released (LATENT HEAT RELEASE)
 Explains how whenever water vapor in the
atmosphere condenses, the air will become
warmer and this warm air will rise.
Convection Currents
34
Atmospheric Convection Currents
► A.C.C.=
Global patterns of air movement initiated
by unequal heating of Earth.
► Hadley Cells: The convection currents that cycle
between the equator and 30 degrees N and S.
 Solar energy warms humid air in the tropics. This warm
air rises and eventually cools below its saturation point.
 The vapor condenses into clouds and precipitation. The
now dry air sinks to Earth’s surface at 30 degrees N and
S.
 As the air descends, it is warmed by adiabatic heating.
This descent of hot, dry air causes desert environments
to develop at those latitudes.
HADLEY CELLS
INTERTROPICAL CONVERGENCE
ZONE
► Intertropical
Convergence Zone (ITCZ)
 The area of Earth that receives the most intense
sunlight, where the ascending branches of the 2
Hadley cells converge.
 It is amplified by dense clouds and intense
thunderstorm activity.
POLAR CELLS
► Similar
to Hadley Cells, the Polar Cells are
convection currents that are formed by air
that rises at 60 degrees N and S and sinks
at the poles (90 degrees N and S).
► Between
Hadley Cells & Polar Cells lies a 3rd
area of circulation, Ferrell Cells.
 Not convection cells; movement driven by
circulation of neighboring cells.
GLOBAL AIR CIRCULATION
RESULTS OF GLOBAL AIR
CIRCULATION
Distributes warm air away from the tropics and cold air away
form the poles
Allows for a wide range of warm and cold air currents to
circulate between 30 and 60 degrees.
Collectively, these convection currents slowly move the warm
air of the tropics toward the mid-latitude and polar regions.
This pattern of air circulation is largely responsible for the
locations of rainforests, deserts, and grasslands on Earth.
Earth’s Rotation & Coriolis Effect
► Rotation
of Earth has important climatic influence,
particularly on the Prevailing Winds.
 As Earth rotates, its surface moves much faster at the
equator than at other regions.
► Imagine
standing still at the equator as Earth rotates
 Given that a single rotation is 24 hours, you would be traveling at
much faster speed at the equator than at the poles.
► The
faster rotation speeds at the equator cause a deflection of
objects that are moving directly north or south.
 The deflection of an object’s path due to Earth’s rotation is called
the CORIOLIS EFFECT
CORIOLIS EFFECT
► Massachusetts
Institute of Tech (MIT)
 http://mit.tv/z79Q8o
► The
prevailing wind systems of the world are
produced by a combination of atmospheric
convection currents and the Coriolis Effect
 If Earth did not rotate, the air within each convection
cell would simply move directly North or South and
cycle back again.
Summary
► Simply
stated, the atmospheric convection
currents of tropical and polar latitudes, the
mixing of air currents in the mid-latitudes,
and the Coriolis effect cause the prevailing
wind patterns that occur worldwide,
although local features, such as mountain
ranges, can alter wind directions.
OCEAN CURRENTS
► Ocean
currents are driven by a combo of
temperature, gravity, prevailing winds, the
Coriolis Effect, and the locations of
continents.
Ocean Currents
► As
we have seen, the tropics receive the most
direct sunlight throughout the year, and tropical
waters are thus generally warm.
► Warm water, like warm air, expands and rises.
 This process raises the tropical water surface about 8cm
higher in elevation than mid-latitude waters.
► This
slight slope is enough for the force of gravity to make
water flow away from the equator.
Ocean Currents: GYRES
►
Large-scale patterns of water circulation that redistribute
heat in the ocean
 Cold water from polar regions moves along the west coasts of
continents, and the transport of cool air from above these waters
causes cooler temperatures on land.
►
Global prevailing wind patterns play a major role in
determining the direction in which ocean surface water
moves away from the equator.
 In the N.H., the trade winds near the equator push water from the
northeast to the southwest and the Coriolis effect deflects this
wind-driven current so that water actually moves from east to
west.
►
The overall effect: Ocean SURFACE currents rotate in a
clockwise direction in the N.H. & in a CCW direction in the
S.H.
Ocean Currents: UPWELLING
► These
explain why some regions of ocean support
highly productive ecosystems.
► Along west coasts of most continents, the surface
currents diverge and cause deeper waters to rise
and replace the water that has moved away. This
upward movement of water to the surface is called
Upwelling.
► The deep waters bring with them nutrients from
the ocean bottom that support large populations
of producers, which support large populations of
fish.
Ocean Currents: THERMOHALINES
►
Thermohaline Circulation: Drives the mixing of surface
water and deep water.
 Crucial to moving heat and nutrients around the globe.
 Driven by surface water that contain unusually large amounts of
salt.
1. Warm water flows from Gulf of Mexico to the North
Atlantic where some of it freezes and evaporates
► 2. The remaining water, now saltier and denser, sinks to
the ocean bottom
► 3. The cold water travels along the ocean floor, connecting
the world’s oceans.
► 4. The cold, deep water eventually rises to the surface and
circulates back to the North Atlantic.
►
Ocean Currents: HEAT TRANSPORT
► Ocean
currents can affect the temperature of
nearby landmasses.
► Ex: The ocean current known as the Gulf Stream
originates in the tropics near the Gulf of Mexico
and flows NE across the Atlantic toward Europe.
As it moves warm waters north, the stream brings
large amounts of heat energy to cooler regions,
moderating temps in latitudes that otherwise
would be much colder.
Concern
► One
major concern about global warming is
that increase air temperatures could
accelerate the melting of glaciers, which
could make the waters of the North Atlantic
less salty and thus less likely to sink.
► Such a change could potentially shut down
thermohaline circulation and stop the
transport of warm water to Western Europe,
making it a much colder place.
ALMOST DONE!!
El Nino-Southern Oscillation
► Earth’s
atmosphere and ocean interact in complex
ways.
► Periodically (every 3 to 7 years), these interactions
cause surface currents in the tropical Pacific Ocean
to reverse direction.
 First, the trade winds near South America weaken,
allowing warm equatorial water from the western Pacific
to move eastward toward the west coast of South
America.
 The movement of warm water and air toward South
America suppresses upwelling off the coast of Peru and
decreases productivity there, reducing fish populations
near the coast.
El Nino-Southern Oscillation
phenomenon is called El Nino (“the baby
boy”) because it often begins around the
December 25 Christmas holiday.
► El Nino can last from a few weeks to a few years.
These periodic changes in wind and ocean
currents are collectively called the El NinoSouthern Oscillation (ENSO)
► Globally, the impact of ENSO includes cooler and
wetter conditions in the southeastern US and
unusually dry weather in southern Africa and
Southeast Asia.
► This
Rain Shadows
►
►
►
Air moving inland from the ocean often contains a large
amount of water vapor.
This air meets the windward side of a mountain range (the
side facing the wind), it rises and begins to experience
adiabatic cooling.
Because water vapor condenses as air cools, clouds form
and precipitation falls.
 As is the case with Hadley cells, this condensation causes latent
heat release, which helps to accelerate the upward movement of
the air. Thus, the presence of the mountain range causes large
amounts of precipitation to fall on its windward side. The cold, dry
air then travels to the other side of the mountain range (leeward
side), where it descends and experiences higher pressures, which
cause adiabatic heating.
RAIN SHADOWS
 This now warm, dry air produces arid conditions
on the leeward side of the range forming a
region called a RAIN SHADOW.
► It
is common to see lush vegetation on the
windward side of a mountain range and
very dry conditions on the leeward side.