Unformatted text preview: ISP217 ISP217 Atmospheric Circulation
Dr. Peacor Outline Basic properties of air How air properties affect climate Earth’s heat distribution and seasons Earth’s wind patterns 2 Answer questions like: Why are there seasons? Why is one part of the world warmer than another? Why are there deserts and why are they where they are? Why is there wind?! (That is, what causes wind?) Why are there windy areas over some parts of the seas, and “doldrums” over others? Outline 3 Basic Properties of Air: Atmosphere Composition Mixture of 78% nitrogen (N ), 21% oxygen (O ) 2 2 Less than 1% argon, carbon dioxide, neon, helium, methane… Water vapor (H O) can occupy up to 4%
2 4 Basic Properties of Air: Density of air Denser air is heavier (by definition). Density of air is affected by Temperature Water content 5 Basic Properties of Air: Density of air Temperature affects air density The molecules in cold air are moving slower….so they occupy LESS space…so cold air is denser than warm air Warm air will rise, cold air will descend Examples?
6 Basic Properties of Air: Density of air Humidity affects density of air Which is more dense (heavier): humid air or dry air? Reason: Water vapor takes up room Water vapor (H2O) displaces HEAVIER oxygen (O2) and nitrogen (N2) gas molecules. 7 Basic Properties of Air: Air pressure Air near the earth is packed densely from all the air pressing down on it in the atmosphere At a higher altitude there is less air pressing downward and air pressure is less 8 Effects of air movement Basic Properties of Air: What happens when air rises to higher altitudes? 1. It expands It expands because pressure is lower 2. It Cools It cools because expansion leads to cooling (PV = nRT) Example: Air coming out of a tire is cool 9 Effects of air movement Basic Properties of Air: 3. It may rain. Cold air can hold less water than warm air: So water (in rising air) may condense and fall. 1+2+3. Rising air rain or snow: When warm air rises, it expands, cools off and can not hold as much water vapor…so it rains/ snows 10 Effects of air movement
Example of how air movement affects climate: Rain shadow
Wet green side Very dry brown side Basic Properties of Air: 11 Rain shadow
Air rises, expands and cools. Result: rain on windward side Moist air Wind Evaporation Dryer air blows to leeward side, sinks and warms up. Result: dry warm area, called a rain shadow. windward side: Wet Leeward side Dry
12 Rain shadow 13 Field Trip Big IslandHawaii 14 15 16 17 18 Class question Which side of the island gets 128 inches, and which side gets 10 inches, of rain a year? Why? Explain the large difference. Important: The wind comes off the Pacific Ocean from the East 19 20 Example 2: Atmospheric convection (mixing) Effects of air movement
2) Rising air expands, cools, relative humidity rises until condensation of water vapour occurs above condensation level. Basic Properties of Air: Condensation level 1) Air warms by contact with warm ground surface, becomes less dense and rises Ground 21 Example 2: Atmospheric convection (mixing) Effects of air movement
Condensation level: Height at which air becomes saturated because of cooling (due to expansion) and condenses into cloud. = Height of bottom of cloud formation. Basic Properties of Air: Condensation level Ground 22 23 24 25 Example 3: Weather Front & Cloud Formation: When warm air meets cold air
2. Rising air expands, cools and relative humidity rises. 3. Clouds form as water vapour condenses above condensation level (white line). 1) Warmer, lighter air is forced to rise by denser cooler air. Cloud Effects of air movement Basic Properties of Air: 1) Cooler, denser air sinks Condensation downwards and level forces lighter, warmer air to rise Ground 26 NE PIC TO W Heat distribution on Earth Why does the equator get so much more heat than the rest of the planet? 27 a b
1) Unequal heat distribution: same amount of energy in less area when closer to equator. Can see this in figure by area of a greater than area of b. 28 a b
1) Unequal deflection and absorption of sun rays by atmosphere: less when closer to equator. Can see this in figure by length of column a greater than length of column b. 29 Heat distribution on Earth Why is it hotter in the summer than in the winter? 23.5 degree tilt of Earth Northern hemisphere leans toward Northern sun in June and away from sun in December December 3 times more light energy in June times than in December than 30 Northern hemisphere summer Northern hemisphere winter 31 Global circulation of air: wind
Three main factors 1. Uneven solar heating 2. Earth’s rotation and the Coriolis effect Earth rotates to the East One rotation per day 3. Continents and Topography
32 Not cause of wind: Big guy with big cheeks: 33 Atmospheric Circulation Cells The air that is heated most, around the equator, rises through the troposphere, hits the stratosphere, and instead of going on into space, starts moving laterally across the top of the troposphere. Up there, it cools. When it cools, it starts to sink. 34 Atmospheric Circulation Cell 35 Theoretical model of wind…if earth did not rotate BUT: Coriolis effect brakes up this pattern as we will see… 36 Video Link http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/ http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw http://www.youtube.com/watch?v= mcPs_OdQOYU (northern hemisphere – moves to the right) 37 Coriolis Effect 38 Coriolis Effect Quito is due south of Buffalo. 39 Quito is on equator: travels at 1036 mi/hr Buffalo is at 45 N: travels at 783 mi/hr So something moving north to south will fall behind the straight southward direction (in northern hemisphere) since north moving slower than south.
40 Coriolis Effect: From Buffalo Earth spinning: object moving south to equator “falls behind” and veers west 41 Coriolis Effect: From Quito Earth spinning: object moving north from equator veers east 42 Video Link http://www.classzone.com/books/earth_science/ter 43 As air moves from south to north in the northern hemisphere, it is deflected to the east by the Coriolis effect. As air moves from north to south in the southern hemisphere, it is deflected to the east by the Coriolis effect. 44 Theoretical model of wind…if earth did not rotate. Because of Coriolis effect, this is not what happens. 45 3 cell model of atmospheric circulation
Air moving up low pressure Solid lines -Little air movement Windy between solid lines Air moving down high pressure 46 3 cell model of atmospheric circulation Just another picture 47 Theoretical vs. Actual Large reason for difference: Land mass effects. 48 Effect of wind patterns on climate:
At the equator (0°) and 60°N and 60°S: Rising air cools and the moisture in it wrings out as clouds and rain • A belt of wet climate occurs • Pressure is low At 30° N and S and at each pole: Falling air warms, and sucks moisture into it like a sponge • A belt of dry climate, deserts, occurs. • Pressure is high Note how dry and wet alternate every 30°. 49 50 Deserts of the World 30° 0° 30° 51 Horse latitude Doldrums Horse latitude 52 Main wind belts The Coriolis effect gives rise to the three main wind belts in each hemisphere at the surface: ∙ The easterly trade winds in the tropics ∙ The prevailing westerlies in midlatitudes ∙ The polar easterlies 53 Doldrums, ITCZ Doldrums, ITCZ: The doldrums are the region near the equator where the trade winds from each hemisphere meet. This is also where you find the intertropical convergence zone (ITCZ). It is characterized by hot, humid weather with light winds. Major tropical rain forests are found in this zone. 54 Horse latitudes The horse latitudes are the region between the trade winds and the prevailing westerlies. In this region the winds are often light or calm. 55 Answer questions like: Why are there seasons? Why is one part of the world warmer than another? Why are there deserts and why are they where they are? Outline Why is there wind?! (That is, what causes wind?)
Why are there windy areas over some parts of the seas, and “doldrums” over others? 56 ...
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This note was uploaded on 03/23/2010 for the course ISP 217 taught by Professor Peacor during the Spring '08 term at Michigan State University.
- Spring '08