Transcript Phys. 102: Introduction to Astronomy

SOAR 2005
Earth’s Atmosphere and Wind
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 1.3810 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)
Inner Planets
Mercury
 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 Temperature
Troposphere
(“mixing” sphere)
 0 – 8 km at poles,
0 – 18 km equator
 90% of total mass
of atmosphere
 Temperature
decreases with
altitude
Atmospheric Structure
 Layers By Temperature
 Stratosphere (tropopause – 50 km)
 Temperature
increases with
altitude to Ozone
layer
 Mesosphere
(50-80 km)
 Coldest part of
atmosphere
(<T> = -90°C)
Atmospheric Structure
 Layers By Temperature
 Thermosphere
(80km outward)
“heat” sphere due
to particle energies
 From insolation
(UV – X-ray!)
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
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
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!
Wind
 Horizontal motion of air across Earth’s
surface (advection)
 Updrafts – upward motion of air
 Downdrafts – downward motion of air
 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  GM world
 
3  R world
 mmolecule 


 k 
 Pressure Gradient force
 isobar = line of constant pressure
 Pressure Gradient force acts perpendicular
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
Importance of Wind
 Arises due to differences in pressure
Force Newtons

 Pascal  Pa
P
2
Area (meter )
 Distributes





heat
moisture
dust
pollutants
microscopic life
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