Composition of the atmosphere 4/23/12
Crust • Mantle • Outer Core • Inner Core Review of layers of the earth
The gases surrounding the earth. What is the atmosphere?
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) How do ocean and wind currents relate?
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
General Surface Current Patterns http://earth.usc.edu/~stott/Catalina/Oceans.html
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 What are Gyres? 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
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 How do surface currents affect the temperature at the poles?
Surface Currents transport gases, nutrients and pollution • O2and CO2 • Nutrients (upwelling and downwelling) • Pollution dispersal • Impact on fisheries and other resources What else do surface currents transport?
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. Where do ocean currents affected by wind occur?
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. Diagram of Katabatic Winds Some Katabatic Winds • mistral • bora • Antarctica is the • windiest place on earth. Wind speeds of 300 kilometres
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 Weather vs. Climate
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 the earth’s axis = variation in seasons. Tilt of Earth’s Axis
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—June Figure 11.9 A
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. Daily paths of the Sun at 40° N latitude—December Figure 11.9 B
Relationship of Sun Angle and Intensity of Solar Radiation ***Seasonal variations in photosynthetic activity= changes in carbon dioxide levels*** Figure 11.10
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 system is produced by unequal heating of the atmosphere on 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 Winds An imaginary uniform Earth with idealized zonal (continuous) pressure belts
Composition of the atmosphere (Day 2) 4/25/12-4/26/12
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. Atmospheric Density
The force or mass per unit area of a column of air. What is atmospheric pressure?
less overlying weight Due to compressibility, atmospheric mass gradually “thins out” with height. Pressure and Density more overlying weight
Vertical Pressure Profile Pressure always decreases with height. Pressure at surface = 1000 mb Pressure at 18 km = 100 mb 100 mb / 1000 mb = 10% above 18 km or 90 % below 18km Pressure at surface = 1000 mb Pressure at 5.5 km = 500 mb 500 mb / 1000 mb = 50% above 5.5 km
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 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
Vertical Structure of the Atmosphere Updraft has “overshot” the tropopause and entered the lower stratosphere Flattened Anvil cloud top reveals the top of troposphere
Vertical Structure of the Atmosphere • Stratosphere • Area 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
Vertical Structure of the Atmosphere • Mesosphere and Thermosphere • Combined 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
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 are greenhouse gases?
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 is ozone?