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4/23/12
*Composition of the atmosphere
*Review of layers of the earth
*Crust
*Mantle
*Outer Core
*Inner Core
*What is the atmosphere?
*The gases surrounding the earth.
*How do ocean and wind currents relate?
*Coriolis effect
*Ekman’s spiral = top down drag.
*Wind blowing over the ocean can move it due to frictional drag.
*Waves create necessary roughness for wind to couple with water.
*One “rule of thumb” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)
*What is the Coriolis Effect?
*The French scientist, Gaspard Coriolis, first explained the deflection of objects moving over the surface due to Earth’s rotation.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml
*What is Ekman’s Spiral?
Nansen and others exploring the Arctic noticed that ice and surface currents move at an angle to the wind direction. Ekman first explained the mathematics of this phenomena, and why it decreases with depth to produce the spiral pattern.
http://www.humboldt.edu/~gdg1/Spiral.html
http://earth.usc.edu/~stott/Catalina/Oceans.html
General Surface Current Patterns
*What are Gyres?
*Circular pattern of wind and surface current motion
*Prevailing Westerlies and Trade Winds strongly influence these flows
*Clockwise rotation in the Northern Hemisphere, counterclockwise in the Southern
http://earth.usc.edu/~stott/Catalina/Oceans.html
* Surface and Deep-Sea Current Interactions
*Unifying concept: “Global Ocean Conveyor Belt”
http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
* How do surface currents affect the temperature at the
poles? *Surface Currents Transport Heat from the Equator to the Poles
*May serve as “heat sources” to cooler overlying air, “heat sinks” from warmer
*Evaporation and condensation participate in latent heat exchanges
* What else do surface currents transport?
*Surface Currents transport gases, nutrients and pollution
*O2 and CO2
*Nutrients (upwelling and downwelling)
*Pollution dispersal
*Impact on fisheries and other resources
*Where do ocean currents affected by wind occur?
*Wind-driven currents occur in the uppermost 100 m or less
*Density differences causes by salinity and temperature produce very slow flows in deeper waters.
*polar regions radiate away more heat energy than they receive from the Sun in the course of a year. However, they are prevented from becoming progressively colder each year primarily by the transport of heat through the atmosphere and the oceans.
Land and Sea Breezes
Temperature contrasts (the result of the differential heating properties of land and water) are responsible for the formation of land and sea breezes.
Mountain and Valley Breezes
Similar to the land and sea breeze in its diurnal (daily) cycle -Valley breezes occur in the day because air along mountain slopes is heated more intensely than air at the same elevation over a valley floor. -Rapid radiational heat loss in the evening reverses the process to produce a mountain breeze.
Chinook (Foehn) Winds
Caused by pressure systems on the leeward (back) side of mountains which pull air over the mountains. As the air descends it is heated adiabatically. Warm, dry winds sometimes move down the slopes of the Rockies, where they are called Chinooks, and the Alps they are called foehns.These naturally occurring winds can be very harmful to human activities.
Katabatic (Fall)Winds
Cold air over highland areas is set in motion, gravity causes the air to rush over the edge of the highland like a waterfall. Katabatic winds are generally much stronger than a mountain breeze. There must be a strong temperature gradient with the colder air aloft.
•mistral•bora
•Antarctica is the windiest place on earth. Wind speeds of 300 kilometres
Some Katabatic WindsDiagram of Katabatic Winds
*Weather vs. Climate
Weather
*Minutes to months
*Temp, precipitation, cloudiness, pressure, wind, visibility
*What you get
Climate
*The average of weather over time and space
*How the atmosphere behaves over a long period of time
*What you expect
Earth’s Motions• Earth has two principal motions—rotation and revolution.
Earth’s Orientation• Seasonal changes occur because Earth’s position relative to the
sun continually changes as it travels along its orbit.
*Earth-Sun Relationships
*Tilt of Earth’s Axis
Tilt of the earth’s axis = variation in seasons.
*Daily Paths of the Sun at 40° N latitude—June
Figure 11.9 A
In the Summer = the northern hemisphere gets more direct sunlight, so there is more photosynthetic light reactions, which take in carbon dioxide. Therefore, there is LESS carbon dioxide in the atmosphere during the summer.
*Daily paths of the Sun at 40° N latitude—December
Figure 11.9 B
In the winter = the northern hemisphere receives less direct sunlight, so there is less photosynthetic light reactions occurring due to less light. Therefore, in the winter and fall in the northern hemisphere have MORE carbon dioxide.
* Relationship of Sun Angle and Intensity of Solar Radiation
Figure 11.10
***Seasonal variations in photosynthetic activity= changes in carbon dioxide levels***
Single-Cell Circulation Model: Hadley Cells
George Hadley, in 1735, proposed that temperature contrast between the poles and the equator creates a large convection cell in each hemisphere.
Global circulation on a nonrotating Earth. A simple convection systemis produced by unequal heating of the atmosphereon a nonrotating Earth.
Three-Cell Circulation Model
In the 1920’s a three-cell circulation model (for each hemisphere) was proposed.
Features of the circulation pattern:
•horse latitude•trade winds•doldrums•prevailing westerlies•polar easterlies•polar front
Observed Distribution of Pressure and WindsAn imaginary uniform Earth with idealized zonal (continuous) pressure belts
*Composition of the atmosphere (Day 2)4/25/12-4/26/12
* Atmospheric Density
*Density or ppm measure the concentration of gases.
*Density = Mass/Volume (units of kg/m3)*At surface, 1.2 kg of air per cubic metre.
*Concentration = parts per million (ppm)
*Air is compressible.
*Gas molecules are not attached to each other, and resist being squeezed closer together.
*Because of compression from the weight of overlying air, the atmosphere is denser near the surface than above.
*What is atmospheric
pressure?
*The force or mass per unit area of a column of air.
* Pressure and Density
Due to compressibility,atmospheric massgradually “thins out”with height.
less overlying weight
more overlying weight
Vertical Pressure Profile
Pressure always decreases with height.
Pressure at surface = 1000 mbPressure at 5.5 km = 500 mb
500 mb / 1000 mb = 50% above 5.5 km
Pressure at surface = 1000 mbPressure at 18 km = 100 mb
100 mb / 1000 mb = 10% above 18 km or 90 % below 18km
Vertical Structure of the Atmosphere
Thermal Layers of the Atmosphere
Four distinct layers of the atmosphere emerge from identifiable temperature characteristics with height
Troposphere
Stratosphere
Mesosphere
Thermosphere
Vertical Structure of the Atmosphere
Troposphere
The lowest layer, named as this region promotes atmospheric overturning
Layer of virtually all weather processes
Warmed at the surface by solar radiation
Identified by a steady temperature decrease with height
Thinnest layer, but contains 80% of the mass
Due to thermal expansion, the tropopause is roughly 16 km over the tropics, but only 8 km at poles
An excess of ozone is “Bad” here.
Vertical Structure of the Atmosphere
Flattened Anvil cloud top reveals the top of troposphere
Updraft has “overshot” the tropopause and entered the lower stratosphere
Vertical Structure of the Atmosphere
StratosphereArea of little weather (“stratified”)
A layer where temperature increases with height
Inversion caused by the absorption of ultraviolet radiation by ozone
Although the ozone layer exists through an altitude between 20-30 km (12-18 mi), actual concentration of ozone can be as low as 10 ppm
The ozone layer is “good” here
Vertical Structure of the Atmosphere
Mesosphere and ThermosphereCombined the two layers account for only 0.1% of total atmospheric mass
Mesosphere, which extends to about 80 km (50 mi) is characterized by decreasing temperatures with height and is the coldest atmospheric layer
The upper most layer; slowly merges with interplanetary space and is characterized by increasing temperatures with height
Temperatures approach 1500oC, however, this only measures molecular kinetic energy as the sparse amount of mass precludes actual heat content
*What gases compose the atmosphere?
*Nitrogen - 78.084%Oxygen - 20.95%Argon - 0.934%Carbon Dioxide - 0.036%Neon - 0.0018%Helium - 0.0005%Methane - 0.00017%Hydrogen - 0.00005%Nitrous Oxide - 0.00003%Ozone - 0.000004%
*Water = 1-4% usually when air is wet
*What is Global Warming?
*An increase in the earth's average atmospheric temperature.
*Mean temperature globally has increased 0.5ºC in the past 100 years
*Absorption of infrared radiation by atmospheric greenhouse gases, increases the avg. temp of the atmosphere.
*Irreversible tipping point of global warming = 450 ppm. (recall from “an inconvenient truth” that it had never gone above 300ppm)
*What are energy waves?
*What are greenhouse
gases?
*Any atmospheric gas that effects the atmosphere by absorbing the infra-red radiation that is reflected off the surface of the earth.
*Carbon dioxide (CO2)
*Nitrous oxides (N2O)
*Methane (CH4)
*CFC’s (chlorinated flourohydrocarbons)
*What is ozone?
*Ozone = O3
*Ozone in the troposphere (ground level)= bad
*Due mostly to motor vehicles
*Strong oxidant
*Respiratory irritant
*Ozone in the stratosphere = good
*Absorbs harmful Ultraviolet radiation (UV-C and UV-B) that cause Basal cell carcinoma (most common) and melanoma (deadliest).
*We are “burning a hole” in the ozone layer in the stratosphere with CFC’s (reduced by Montreal Protocol)
*What are CFC’s?
*CFC’s = Chlorofluorocarbons
*Developed in the 1930’s and used in a lot cooling agents and cleaning solvents.
*Deplete the ozone layer in the stratosphere, which typically helps to keep out unwanted UV-C and UV-B rays.
*What are nitrous oxides?
*Nitrogen and oxygen compounds (Nox) that can be oxidized by oxygen gas or ozone in the troposphere to create Acid Rain/Acid deposition (HNO3).
*Green house gases produced by burning fossil fuels.
*Formed in a process of nitrification.
*Where does methane come
from?
*Methane (CH4) is frequently produced from decomposing organic matter, such as fecal matter from domestic livestock.
*Where does carbon dioxide
(CO2) come from?
*The primary concentration of carbon dioxide (CO2) in the atmosphere is due to burning fossil fuels.
*It is also released when organic matter becomes due to respiration of decomposing bacteria.
*It is released through respiration.
*Concentrations of CO2 are decreased by light reactions of during photosynthesis.
*What does sulfur dioxide? *Mostly produced
by burning fossil fuels and volcanoes, coal mines (acid mine drainage).
*Causes acid deposition in the form of H2SO4 (sulfuric acid)
*What is Acid deposition?
*commonly known as acid rain, occurs when emissions from the combustion of fossil fuels and other industrial processes undergo chemical reactions in the atmosphere and fall to the earth as wet deposition (rain, snow, cloud, fog) or dry deposition (dry particles, gas)
*An increase in concentration of heavy soluble metals in a local pond = acid deposition
*What are particulates?
*How do humans pollute the air?
*1) Industry
*2) Transportation
*3) Energy production
*How does burning fossil fuels affect the
atmosphere?*Releases Sox, Nox, CO2 into the atmopshere.
*Increases likelihood of acid rain/Increases acid deposition
*Increases particulates in the air
*What could result from global warming?
*1) coastal flooding and submerged low lying areas
*2) Thermal Expansion of oceans, which result in an increase in sea level.
*3) Expanding range of tropical diseases
*4) More intense hurricanes and typhoons
*5) Increase in crop damage from pests and diseases.
*6) Loss of carbon sinks such as coral reefs, which are composed of CaCO3
*How is the artic especially
affected by global warming?
*Positive feedback loop- increase in global warming results in a decrease in ice (which reflects much of the sun’s rays), increasing surface area of water, which absorbs most of the sun’s rays, heating the water and perpetuating the cycle.
*What are potential
solutions?
*1) Use renewable resources to replace fossil fuels.
*i.e. replace coal burning electricity with wind or solar farms.
*2) Increase policy incentives and regulations to reduce fossil fuel emissions and push the economy toward more sustainable practices.
*i.e. fund public transit options, creation of bike lanes and green building practices.
*What are some examples of attempts to internationally regulate
air quality?
*Montreal Protocol
*Kyoto Protocol
