Transcript Phys. 102: Introduction to Astronomy

SOAR 2005
Energy and Circulation in the
Atmosphere
Earth
 Complex atmospheric evolution
 Primordial Atmosphere Lost to space
 H & He very light molecules, escape easily
 Initially like Venus & Mars: mostly CO2
THEN
 Water condensed into oceans
 Oceans absorbed CO2
 Locked it into rocks (CaCO3 = limestone)
 Life flourished in oceans
 Released free oxygen
 Sedimentary rocks turned red
 Ozone layer formed
Evolution of Earth’s Atmosphere
Oxygen
content
created,
maintained
by life.
Atmospheric
Structure
 Layers (from surface) due to
 Density (Pressure)
 Radiation Environment
 Temperature
Atmospheric
Structure
 Layers By Function
 Ozonosphere (O3 layer)
 Upper portion of
Stratosphere
 Absorbs UV (0.1-0.3 nm),
radiates IR
Ozone constantly created
Warmest layer in
& destroyed by UV,
atmosphere
CFC’s increase destruction
 Harmed by CFC’s
Cl + 2O3  Cl + 3O2 …
and Cl is free to kill
again!
Hole in the ozone layer over Antarctica
Air Pressure
 Pressure is force/area
= weight of air column
 1 in2 column
 weight = 14.7 lb
 1 m2 column
 weight = 10 tonnes
 1 tonne = 1000 kg
= 2204 lb
 Why doesn’t the air
pressure crush you when
you lie down?
Air Pressure
 Standard Atmosphere




760 mm Hg
29.92 in Hg
33.9 ft. H2O
1013 millibars (mb)
 1013 hPa
hectopascals
Weight of Hg = Weight of Air
Hg(tube area)(column height)
= (air presure)(bowl area)
Weight of
column of Hg
Weight of column of air
Driving Forces
 Gravitational Force
 Earth’s gravity holds atmosphere
TEscape
2  GM world  mmolecule 
= 



3  R world  k 
 Pressure Gradient force
 isobar = line of constant pressure
 Pressure Gradient force acts perpendicular
Driving forces
 Pressure Gradient force
 from high pressure to low pressure
Driving Forces
 Coriolis Force
 Acts ONLY ON MOVINGr objects
r

 proportional to velocity ( F v )
 perpendicular to velocity
 acts over large distances
force
velocity
 Does not determine direction water spins down a drain!
The rolling ball follows a
straight path seen from
above, a curved path seen
from the rotating
reference frame (riding on
the merry-go-round).
Different
latitudes
“orbit” axis
at different
speeds.
Projectile carries
small speed, falls
behind high speed
equator.
Coriolis Force
Coriolis Force
 All moving objects are deflected
 to their right in northern hemisphere
 to their left in southern hemisphere
Coriolis force
deflects velocity no
matter what the
original direction of
the velocity!
Coriolis Force: All moving objects are
deflected
to their
right in
northern
hemisphere
to their left
in southern
hemisphere
Coriolis Force
Northern Hemisphere
Southern Hemisphere
Moving objects
deflected to their own
right.
Moving objects
deflected to their own
left.
Tropical Cyclone Olyvia
L
L
Hurricane Isabel
Storms rotate
counterclockwise
Storms rotate
clockwise
Cyclones & Anticyclones
 Cyclone – circulation around low pressure
 CCW in northern hemisphere
 CW in southern hemispere
 Anticyclone – circ. around high pressure
 CW in northern hemisphere
 CCW in southern hemisphere
http://www.usatoday.com/weather/tg/whighlow/whighlow.htm
Energy Budget
 Insolation
 Sun’s incident energy drives air motions
(energy from deep interior adds a tiny bit)
 Distribution of Sunlight
 Reflection from clouds, landscape
 Absorption by atmosphere
 Absorption by surface
 Albedo = ratio of sunlight reflected
 Earth: 0.367
 Moon: 0.113
 Mars: 0.15
 Venus: 0.84
Insolation: 1,373 W/m2
Most solar energy comes in as
light (shortwave radiation)
30% Reflected by
atmosphere
20% Absorbed by
atmosphere
50% Absorbed by
Earth’s surface
Greenhouse Effect
 Light from sun gets absorbed by Earth
 Earth radiates infrared
Greenhouse Effect
 Light from sun gets absorbed by Earth
 Earth radiates infrared
infrared
Earth re-emits
energy absorbed
from sunlight as
infrared
Greenhouse
Effect
IR gets absorbed by
atmosphere
 Air heats
 Air absorbs more
water
 Moist air absorbs
more IR & heats more
 absorbs more
water
Energy Flow from Surface
7% conducted to air
23% transferred by water
20% radiated
as IR
(longwave)
% of total
insolation
Energy Transfer
 Convection – hot stuff moves
 Conduction – hot stuff heats neighbors
 Radiation – heat moves as IR radiation
Energy Transfer by Water
 Specific Heat
 Energy absorbed/released to change temp.
 Latent Heat
 Energy needed to change phase
(substance remains at same temperature)
Energy Transfer by Water
 Specific Heat
 Energy absorbed or
released to change temp.
Raising 1 kg of
water 1°C
absorbs 4,168
Joules
1 kg
10 cm
square
cube of
water
Substance
Specific Heat
(Joule/K/kg)
Air (50C)
1050
Iron or Steel
460
Lead
130
Glass
840
Quartz
762
Granite
804
Sandstone
1088
Shale
712
Soil (average)
1050
Wood (average)
1680
Ice
2100
Steam
2050
Water
4168
4000 Joules ≈ energy to lift 400 kg or 900 lb 1 m
Energy Transfer by Water
 Latent Heat
Specific Heat (Joule/kg)
 Energy absorbed or
Substance
released to change phase
vaporization
Evaporating 1 kg
of water
absorbs
2,257,000Joules
1 kg
fusion
Alcohol
879,000
109,000
Water
2,257,000
333,500
10 cm
square
cube of
water
2,257,000 Joules ≈ energy to lift 225,700 kg or 507,000 lb 1 m
Energy Transfer by Water
 Latent Heat
 Energy needed to change phase
(substance remains at same temperature)
 Absorbed by surface water
 Released by water condensing to clouds
Energy Absorbed by Atmosphere
% of total
insolation
20% from Sun
7% conducted from surface
23% transferred by water
8% radiated by surface
Energy Emitted by Atmosphere
% of total
insolation
30%
reflected
directly to
space
58%
emitted as
IR
Complete Energy Budget
Global Warming
Increasing greenhouse
gases decreases longwave
(IR) radiation lost to
space
Increasing greenhouse gases
increases absorption of
longwave (IR) radiation by
ground
Venus: Greenhouse gone wild!
The
difference
between Earth
and Venus!
Temperature Controls
 Sunlight heats land, water, air
 Land warms, heats air
 Air circulates
 Convection cells
 warms -> expands -> rises
 cools -> contracts -> sinks
 Water circulates
 Currents driven by wind & Earth rotation
 Water temperature increases SLOWLY
 Large energy change needed for small temp. change
Convection Cells
 Hot surface heats air
 Air expands,
 becomes less dense than surroundings
 rises, spreads out at top
 Air aloft cools,
 becomes more dense than surroundings
 sinks, spreads out on surface
Atmospheric Circulaton
Rising Air
 Cools
 Water vapor condenses
(usually) results in clouds
 Lowers surface pressure
Atmospheric Circulaton
 Falling Air
 Warms
 DRY (lost mosture rising)
 Increases surface pressure
Atmospheric Circulation
Sunlight heats ground
Ground heats air , drives convection from
subsolar latitude
Subsolar latitude
is 0º on the
equinoxes
Maximum Insolation
Subsolar latitude
is 23.5º N/S on
the solstices
Atmospheric Circulaton
Air rises
from subsolar
latitude,
clouds form &
precipitate,
air aloft
moves N & S,
cools, dries &
sinks at
about 30º N
&S
Driven by heating near
equator
Dry air falling
 Arid
Moist air
rising  humid
Air spreads
N & S on
surface
Air aloft cools
until it sinks
Atmospheric Circulaton
Cold, dry air falling  Arid
Air warms and
moistens along
surface
Air from
aloft sinks
near poles,
moves N &
S along
surface
Driven by cooling
near poles
Surface flows
converge, rise
Dry air falling
 Arid
Moist air
rising  humid
Moist air rising
 stormy
Dry air falling
 Arid
Moist air rising
 stormy
Dry air falling
 Arid
InterTropical
Convergence
Zone
Rising Air:
Low
Pressure
Pressure Zones
Pressure Zones
Falling Air:
High
Pressure
Pressure Zones
Pressure
Zones:
air motion
is vertical
so there is
little wind!
Wind
Zones
Winds:
Falling air
spreads
North &
South along
surface.
But the winds don’t go straight!
Winds
named
for
direction
they are
from
Windless
zones
names vary
Wind Zones
Easterlies
Polar Front
Westerlies
Horse Latitudes
NE Trades
Doldrums
SE Trades
Horse Latitudes
Westerlies
Polar Front
Easterlies
General Atmospheric Circulation
ITCZ
STHPC
Polar High
Polar
Easterlies
Doldrums
Polar Front
Horse Latitudes
 Cross sectional view
Westerlies
Easterly
Trades
World Pressure Cells: January
North American High
H
Aleutian
Low
Islandic
Low
Siberian
High
Parallel isobars over (low friction) ocean ⇒ rippin’ winds!!!
World Pressure Cells: January
Tibetan
Low
Parallel isobars over (low friction) ocean ⇒ rippin’ winds!!!
Upper Atmospheric Winds
 Jet Streams: Fast Winds Aloft
Polar Jet Stream
 Above Polar Front (midlatitude air meets polar)
 Rossby waves move loops north & south
 7,600 – 10,700 m (25-35 kf)
 speeds up to 300 kph (190 mph)
Upper Atmospheric Winds
 Jet Streams: Fast Winds Aloft
 Subtropical Jet Stream
 above Subtropical highs (tropical air meets
midlatitude)
 9,100 – 13,700 m (30-35 thousand feet)
 speeds less than Polar Jet Stream
Polar Jet Stream
 Determines N.Am. winter weather
 Strong west wind
 monitored by
weather
balloons
Check out PBS’s explanation!:
www.pbs.org/wgbh/nova/vanished/jetstream.html
Polar Jet Stream
 Determines N.Am. winter weather
 Rossby waves bring cold air south