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 BreezesTemperature 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) WindsCaused 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)WindsCold 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 AxisTilt 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 CellsGeorge 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 ModelIn 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

Vertical Structure of the Atmosphere

Troposphere The lowest layer, named as this region promotes atmospheric overturningLayer of virtually all weather processesWarmed at the surface by solar radiation Identified by a steady temperature decrease with height Thinnest layer, but contains 80% of the massDue to thermal expansion, the tropopause is roughly 16 km over the tropics, but only 8 km at poles

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 heightInversion 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

Vertical Structure of the Atmosphere

Mesosphere and ThermosphereCombined the two layers account for only 0.1% of total atmospheric massMesosphere, which extends to about 80 km (50 mi) is characterized by decreasing temperatures with height and is the coldest atmospheric layerThe upper most layer; slowly merges with interplanetary space and is characterized by increasing temperatures with heightTemperatures 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?

*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)