Atmosphere

1. Atmosphere

2. Composition • The atmosphere is made of a variety of gases, roughly in the following proportions: • 78% Nitrogen • 20% Oxygen • 1% Argon • <1% Carbon Dioxide • <1% Water vapor

3. Air temperature • This is the average speed or kinetic energy of all the particles in a mass of air. • Temperature can affect density and pressure.

4. Air pressure • This is the result of gravity pulling the air above down, exerting pressure. • It is also the result of density: how many air molecules are in a volume. • Denser air in general presses “down” more due to gravity.

5. Buoyancy • Less dense substances or objects are buoyant: they float. • Hot air is made of fast-moving particles. As they bounce around, they spread out, become less dense, and become buoyant. • Cold air is made of slower moving particles. They can bunch together more closely, be more dense, and become less buoyant.

6. Trends • In general, closer to ground level means: • Air will be denser that air above it. • Air pressure will increase compared to air above it. • Air temperature will increase compared to air above it (with a few exceptions.) • The amount of air pressure at sea level is known as 1 Atmosphere of pressure. (1 ATM)

7. Troposphere • The troposphere stretches from the surface to up to 20 kms in the air. (About the distance from here to Orland Park) • Almost all air movement occurs in the troposphere. • All weather occurs in the troposphere. • The troposphere is the warmest and densest layer, but cools near the top.

8. Stratosphere • The stratosphere extends from 20 to 50 km in the air. • The stratosphere contains a layer of ozone (O3) that absorbs ultraviolet light before it can reach Earth’s surface. • The stratosphere warms near its top because of the energy the ozone layer absorbs. • As altitude increases, air pressure continues to decrease.

9. Mesosphere • Temperatures continue to drop as you rise through the mesosphere. • Falling meteors experience enough friction in the mesosphere that they heat up to become glowing hot: falling stars. • Most meteorites burn up completely as they fall. • Ice clouds are sometimes found in this layer.

10. Thermosphere • In this layer, temperatures begin to rise again. As the atmosphere gets thinner (density and pressure decrease) the remaining particles absorb so much energy from the sun that they are very hot, if rarely found. • This is where the International Space Station and most satellites are found.

11. Exosphere • The exosphere is what we would consider “outer space.” • Here, gases are so thin and spread out, that the temperature, pressure and density are basically zero. • In the exosphere, there is so little matter to absorb electromagnetic energy that electromagnetic waves can go on forever.

12. Atmosphere Conditions • Temperature increases with direct sunlight and longer days. • Temperature: average temperature increases closer to the equator, and decreases closer to the poles.

13. Evaporation II • When fast moving particles leave an object, the average speed of the remaining particles drops. • Evaporation therefore lowers temperatures/cools objects. • Evaporation is therefore a mechanism to transfer heat from objects to the surrounding environment.

14. Evaporation • Liquid water contains molecules moving at a variety of speeds (kinetic energy.) • Temperature is the average of particle/molecular speeds in a substance. • The fastest moving particles are the most likely to break free and become gaseous water vapor.

15. Humidity • The amount of vapor present in the air is this, because molecules of gaseous water can diffuse into the air.

16. Relative humidity • This is the percentage ratio of the amount of current water vapor present in the air compared to how much vapor that air could hold. • When comparing different areas that contain the same amount of water vapor: • Areas that can’t contain much vapor tend to have high relative humidity. • Areas that can contain a lot of vapor have low relative humidity. • Liquid water evaporates the most quickly and easily in environments with low relative humidity.

17. Electrical Current • Electrons can get scraped up by blowing air currents. • This leaves a positive charge on the ground. • Insulators can let electrons stick to their surfaces, but have high resistance to allowing electrons to travel over or through them. • Pure water and air are insulators with high resistance.

18. Lightning • When enough electrons are trapped on the surface of insulating water droplets (usually in clouds) they can force their way across air molecules as a current. • This superheats the air, turning it into an ionized gas: plasma. • This glows white hot: lightning.

19. Thunder • The heat produced by electrical current through air causes the air to expand. • The rapid expansion of air causes a shockwave. • This shockwave is perceived as a loud noise.

20. Wind patterns • As air warms, it rises. • As air cools, it sinks. • Air near a heat source such as warm water or land will tend to heat up, rise, cool, and then sink back down. These loops of moving air are convection currents.

21. Wind patterns: general • Warm air is less dense, to it usually moves up in the atmosphere, and then towards the nearest pole. • Cool air is denser, so it tends to sink, and move towards the equator. • In general, air currents usually have cool, dense air flowing in to replace buoyant high temperature warm, buoyant air.

22. Coriolis Effect I • The Earth is rotating. • The circumference of the circle a point on the Earth’s surface moves through at the equator is large. • The circumference of a circle a point on the Earth’s surface moves through at the poles is small. • All points on the Earth’s surface rotate 360 degrees once every 24 hours. • Points closer to the equator are moving faster than points closer to the poles.

23. Coriolis Effect II • As moving air shifts north/south and changes latitude, it retains the speed of the Earth’s rotation from its point of origin. • When moving away from the equator, the air is moving East faster than the Earth below it, causing it to curve Eastward. • When moving towards the equator, the air is moving eastward slower than the Earth below it, causing it to curve westward.

24. Coriolis Effect III • In the Mid-Latitude Cell, the rotation of the Earth causes winds along the surface to move away from the poles. • We are in a Mid-Latitude Cell. • As air moves away from the poles, it curves Eastward. • The air in “our” cell therefore moves from the southwest to the northeast, in general.

25. Wind patterns: cells • There are three distinct zones of air circulation: • From the equator (0 degrees) to 30 degrees are Hadley Cells. • From 30 degrees to 60 degrees are Ferrel/Mid-Latitude Cells • From 60 to 90 degrees are Polar Cells.

26. Cell rotation direction • In Polar and Hadley cells, air close to the equator is heated by land/water heated by the sun. • This air becomes buoyant as it warms, and moves towards the poles, where it cools and sinks before moving towards the equator. • In both these cells, air moving along the ground is usually moving towards the equator.

27. Cell rotation direction II • Mid-latitude/Ferrel cells rotate air mainly because of friction with adjacent Polar and Hadley Cells. • The air in Ferrel Cells rotates in the opposite direction from its neighboring cells – air moving along the ground as wind is typically moving away from the equator and towards the poles.

28. Cells and Coriolis Effects • Because the air in different Cells moves in different directions along the ground, due to the Coriolis Effect, the wind at ground level curves in different directions. • Polar and Hadley: Northeast to Southwest (Easterlies due to the direction of origin.) • Mid-Latitude/Ferrel: Southwest to Northeast (Westerlies)

29. Weather and Condensation • Moving masses of air along the ground cause wind. • A distinct mass of air with a distinctive temperature, pressure and density can be called a FRONT. • Cold fronts are cooler and denser than surrounding air. The are represented with blue lines on weather maps. • Warm fronts are warmer and less dense than surrounding air. They are represented by red lines on weather maps.

30. Weather and Condensation II • When Cold Fronts and Warm Fronts meet, condensation can occur. • Cool air absorbs heat from warm air, causing it to cool. • Water vapor in the (formerly) warm air condenses as it cools to form clouds.

31. Weather and Pressure • A barometer is an instrument that measures the pressure from the weight of air in a location. • Denser air exerts more weight/pressure, causing a barometer reading to rise. This indicates cooler air is moving into an area, likely causing condensation and cloudy weather. • Buoyant air exerts less pressure, causing the barometer reading to fall. This indicates warmer air is moving into an area, likely causing clearer skies.

32. Temperature Inversions • Cool air is denser and less buoyant, so it sinks. • Sometimes, Cool/Dense air can end up above Warm/Buoyant air. • This is unstable, and can sometimes result in violent weather if the air masses cannot mix easily.

33. Vortexes • These occur when masses of different density are unbalanced, with a dense mass above a less dense mass. • If the difference between the masses is extreme, they cannot mix. • If they cannot mix, they must change positions. • To change positions, each mass takes the lowest energy path: a spiral. • This spiral exchange results in a vortex.

34. Hurricanes • When solar energy warms open water with a Cold Front on top: • Warmed water evaporates. • This creates a mass of warm air above the water, but beneath the colder air above. • This can sometimes result in a vortex. • As long as there is a source of warmer air and evaporating water, this vortex will continue. • In the northern hemisphere, such vortexes are called Hurricanes. • In the Southern Hemisphere, they are called Cyclones. • These can last days and even weeks, and can cover thousand of miles.

35. Tornadoes • When masses of air of different densities meet, sometimes they do not mix well. • If a cold mass “slides” atop a warm mass of air, a temperature inversion can result. • If the densities of the air masses are different enough that they cannot mix, sometimes a vortex can form. • These are tornadoes. They typically last less than hours, and cover small areas.

36. Altitude and Condensation • As air moves to higher altitudes, it cools. • Cooler air experiences condensation • Condensation can lead to precipitation. • As air increases in altitude, it tends to lose humidity. • As air flows over a mountain, condensation occurs on the windward side, causing humidity to drop. • As air flows over a mountain, once it reaches the lee side, humidity is usually low.