Transcript LCHS - A.P. Environmental Science

Atmosphere and
Weather
AP Environmental Science
.
www.ai.mit.edu/people/jimmylin/pictures/2001-12-seattle.htm
Origin of Modern Atmosphere
• original atmosphere surrounded the homogenous planet
Earth and probably was composed of H and He
• second atmosphere evolved from gases from molten
Earth
– H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3, and
CH4
– allowed formation of oceans and earliest life
• modern Atmosphere
– evolved after Cyanobacteria started
photosynthesizing
– oxygen produced did not reach modern levels until
about 400 million years ago
Atmosphere
Layers
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Exosphere
Thermosphere
(Ionosphere)
Mesosphere
Stratosphere
Troposphere
Composition
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Nitrogen (N2, 78%)
Oxygen (O2, 21%)
Argon (Ar, 1%)
myriad of other very
influential components are also
present which include the Water (H2O, 0 7%), "greenhouse" gases or Ozone (O3, 0 0.01%), Carbon Dioxide (CO2, 0.01-0.1%),
Solar heating of earth
Solar radiation
strikes the earth at
different angles
based on the
latitude.
At high latitudes –
near the poles the
sun’s energy is
spread out over
larger area
At low latitudes –
near equator the
sun’s energy is
concentrated in a
small area
Seasonal
Changes
• Occur because
the earth’s axis is
tilted
• Creates opposite
seasons in the
northern and
southern
hemisphere
• Factor that
determines global
air circulation
patterns
http://www.usatoday.com/weather/tg/wglobale/wglobale.htm
Heating the atmosphere
• Solar energy (UV radiation) is absorbed
– Darker objects absorb more radiation than
lighter objects which reflect radiation
• Albedo – ability to reflect light radiation
• Absorbed radiation converted to heat
(infrared radiation)
• Heat radiates off object and warms
surrounding air
Earth’s Warming Mechanism
• Greenhouse effect
– Natural and Essential Process
– Global Warming is a DESIRED result of the
greenhouse effect
– Without this process the earth would be
uninhabitable
• An INCREASED RATE of Global Warming could
cause global climate consequences
Greenhouse gases
• Contained in the upper troposphere
– Carbon dioxide (CO2)
– Water Vapor (H2O)
– Methane (CH4)
– Nitrogen Oxide (N2O)
• Form a barrier that reflects infrared
radiation and traps it
Greenhouse Effect
UV radiation (short-fast
wavelengths) from sun
penetrates atmosphere
UV Radiation is absorbed
by the earth surfaces
UV Radiation is converted
to heat (infrared radiation –
long-slow wavelengths)
Infrared radiation rises
into the atmosphere
Long slow wavelengths
cannot penetrate the
greenhouse gases in
atmosphere
Heat is trapped in
troposphere warming the
earth’s air and surface.
Circulation of air
• Recall Convection
– Transfer of heat
through a fluid
– Energy warms the air
– density decreases
– Warm air rises
– As air rises it cools –
density increases
– Cool air falls
– repeats
Atmospheric circulation
• Uneven heating of the
earth’s surface
causes temperature
differences
• Temperature
differences create
pressure differences
• Pressure differences
cause air to move
• High pressure air
moves and pushes
low pressure air –
WIND is generated
Coriolis effect
• Non Rotating Earth model
– Winds would blow only from north pole to
equator
• Rotating Earth model
– Rotation of earth creates Coriolis Effect
• Deflection of actions due to earth’s rotation
• Northern Hemisphere rotate to the right
• Southern Hemisphere rotates to the left
– Creates Atmospheric circulation cells and
wind belts
Coriolis efffect
Wind Belts
Three major wind belts created by Coriolis effect
– 60 – 90 degrees latitude Polar Easterlies – winds blow
FROM the east
– 30 – 60 degrees latitude Westerlies – winds blow
FROM the west
– 0 – 30 degrees latitude (equator) Trade Winds – blow
from east to west
Air-Ocean Interaction
• Air circulation causes winds
– Winds cause friction
– Friction moves water
• Creates surface currents
– Currents follow global wind patters
– Currents are deflected by continents
– 6 major circular currents called “gyres”
• Responsible for the movement of heat energy
– moderates local climates
• Gulf stream – moderates eastern US and UK
• California Current – moderates California coast
• Brazilian current – moderates temps of southern South
America
Ocean Currents
• Sea-surface temperature influences air
temperature as the ocean exchanges heat
with the overlying atmosphere.
• It also influences evaporation rates which
are generally higher where sea-surface
temperature is higher
Surface Currents
6 major currents – gyres – rotate clockwise in Northern hemisphere
and counterclockwise in southern hemisphere due to coriolis effect
Deep Currents
• Uneven heating of earth by solar radiation
results in different density of ocean water
– Polar Region
• Low Temps and Presence of Ice
creates
Very Cold, Very Salty water with high density –
sinks rapidly
– Mid latitudes
• Moderate temps create water with lower density
– Equator
• High temps create water with low density
• Dense Polar water sinks and pushes less dense
water out of the way creating deep circulation
current
Global conveyor belt transfers heat energy around the planet
Through upwelling it exchanges nutrients with the surface water
Deep ocean currents store carbon dioxide