Phys. 102: Introduction to Astronomy
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Transcript Phys. 102: Introduction to Astronomy
SOAR 2007
Earth’s Atmosphere and Wind
Course Outline
Course Outline
Atmospheric structure, pressure & wind
Oceanic Circulation
Energy transfer & circulation
Past Climates
Global Climate Change
Origin of Planets
Coalescence of matter in circumsolar cloud
Many Craters
Collisions heat!
Molten interior
Interior layered
Denser materials sink to center
Core mostly Iron (Fe) & Nickle (Ni)
Crust mostly rocky (CaCO3, SiO2, etc)
Planetary Atmospheres
Form from
Gases from planet’s interior (volcanoes)
Gases from impacts (planets)
Terrestrial Planets
Mercury – none
Venus CO2 with H2SO4 clouds
Mars – CO2 with H2O clouds
Earth – N2 with O2
Jupiter & Saturn – H with NH3 clouds
Galilean moons – traces
Titan – N2 with CH4
Uranus & Neptune – H with CH4 clouds
Planetary Atmospheres
Escape Velocity
R from center
Molecular Speed
& Temp
1 2 3
mvavg kT
2
2
3kT
v
m
avg
k 1.3810 23 J
Radius
(kg)
(km)
lb
m/s
1000 mph
SOL
2E+30
695990
4196
617439
1,381
MERCURY
3E+23
2440
57
4248
9.5
VENUS
5E+24
6052
136
10358
23
EARTH
6E+24
6378
150
11174
25
Luna
7E+22
1737
25
2376
5.3
MARS
6E+23
3397
57
5017
11
JUPITER
2E+27
71492
380
59524
133
Io
9E+22
1820
28
2557
5.7
Europa
5E+22
1570
20
2034
4.6
Ganymede
1E+23
2630
22
2749
6.1
Callisto
1E+23
2400
19
2450
5.5
SATURN
6E+26
60268
160
35473
79
Titan
1E+23
2670
19
2597
5.8
NAME
2GM planet
vescape
or
Mass
Weight of
150 lb
person
K
Boltzmann' s Constant
Escape Speed
Planetary Atmospheres
Presence & size due to combination of
Temperature = Distance from Sol
Size of world = escape velocity
Large worlds
Keep atmospheres even close to Sol
Small worlds
Only have atmospheres far from Sol
Composition due to T
Size of world
Escape
2 GM world
3 R world
mmolecule
k
Large worlds keep small molecules (H)
Small worlds keep large molecules (N2, O2, CO2)
Mercury
Inner Planets
Small, hot no atmosphere stays
Venus
Large, hot thick atmosphere
NO WATER H2O H2 + O that binds with C, S, etc
CO2 + H2S04 Clouds
Run-away greenhouse effect
Mars
Small, cool thin atmosphere & thinning
Evidence of ancient oceans but water now present
only as solid and gas
CO2 + H2O Clouds, fogs
Mars & Venus
Both primarily CO2 but very different!
Mars 95.3% CO2
Venus 96.5% CO2
250K – 273K = -23ºC = -10ºF
750K – 273K = 477ºC = 890ºF
Venus: Greenhouse gone wild!
Interaction with Sunlight
Sky is blue because blue scatters, red doesn’t
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 (from surface)
Troposphere –
sphere of weather
Stratosphere –
sphere of ozone (O3)
Mesosphere
Ionosphere –
sphere of ions
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
Atmospheric Structure
Layers By Function
Ionosphere
Thermosphere & Mesosphere
Ionized particles (UV + atoms ions + e- + energy
Absorbs -rays, x-rays, UV, cosmic rays
Reflects AM radio waves
Importance of Wind
Arises due to differences in pressure
Force Newtons
Pascal Pa
P
2
Area (meter )
Distributes
heat
moisture
dust
pollutants
microscopic life
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
Varies with
Air Pressure
altitude (in Pa, H in m)
H
log10 P 5
15500
air motion
rising air = low pressure
subsiding air = high pressure
moving air is at lower
pressure than still (or slower
moving air … wind pulls
curtains against window
screen & airplane wings up!
Air Motion
Updrafts – upward motion of air
Downdrafts – downward motion of air
Wind
Horizontal motion of air across Earth’s
surface (advection)
Measured by anemometers
1 knot = 1 nautical mile/hour
= (1 minute of latitude)/hour
= 1.852 kph = 1.15 mph
Speed and Direction recorded
Driving Forces
Gravitational Force
Earth’s gravity holds atmosphere
TEscape
2 GMworld mmolecule
3 Rworld k
Pressure Gradient force
isobar = line of constant pressure
Pressure Gradient force acts perpendicular
Importance of Wind
Only a difference
in pressure makes
air move.
Driving
Forces
Pressure
Gradient force
Indicated by
density of isobars
Driving
Forces
Pressure
Gradient force
Indicated by
of isobars
18 hPa across
density
~400 km
North America & Greenland,
February 6, 18Z (1 pm EST)
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
Driving Forces
Friction
Friction with ground slows wind
Extends upward ~ 500 m
Varies with surface, time
Surface air slows air aloft
Friction with ground slows wind
Geostrophic Winds
Pressure Gradient Force
creates wind ⊥ to isobars
Coriolis Force
deflects motion to right in N. hemisphere
⇒ deflects Coriolis force!
Forces
Wind deflects due to
Balance
Isobars
Coriolis force
Pressure
Coriolis
Gradient
force Coriolis force acts
perpendicular to new
force
wind direction
wind velocity
wind along isobar
Geostrophic Winds
Pressure Gradient Force
creates wind ⊥ to isobars
Coriolis Force
deflects motion
to its right in N. hemisphere
to its left in S. hemisphere
aligns wind with isobars
Surface Winds: Not Geostrophic
Friction slows winds at surface
Reduces Coriolis force
Pressure Gradient force dominates
Convection Cells
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: July
Hurricane Azores
High
paths!
Tibetan
Low
Monsoon
Winds
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