Gy101 week 10
Gy101 week 10 GY 101
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This 7 page Class Notes was uploaded by Elle Notetaker on Thursday April 7, 2016. The Class Notes belongs to GY 101 at University of Alabama - Tuscaloosa taught by Eben Broadbent in Fall 2016. Since its upload, it has received 52 views. For similar materials see Atmospheric Processes & Patterns in Geography at University of Alabama - Tuscaloosa.
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Date Created: 04/07/16
4/4 Notes taken by Elle Gossman 3 Cell Model generally accepted to show how air circulates around the Earth, proposed by William Ferrel. It divides each hemisphere into 3 cells: 1) Hadley Cell circulates air between the tropical lows and the subtropical highs, at about 2030 degrees latitude. Trade winds are deflected to the left and right in the North and South hemispheres, creating NE trade winds in the north and SE trade winds in the south. The Hadley Cell is strongest in the winter, when there’s the biggest temperature gradient. Goes clockwise. 2) Ferrel Cell circulates air in the midlatitudes, wind shifting from the subtropical highs to the subpolar lows and deflected by the Coriolis Effect to create the Westerlies (wind is named for where it comes FROM) in both hemispheres. Goes counterclockwise. 3) Polar Cell Air is circulated between the polar highs and the subpolar lows, run by thermal differences. Air is directed by the Coriolis Effect, creating Easterlies in both hemispheres. This one goes clockwise. Here’s a video we watched in class: https://www.youtube.com/watch?v=MNQ9z_EbJc Semipermanent Pressure Cells There are a bunch of alternating pressure cells of high and low pressure that shift position with seasons. Deserts conditions at certain latitudes are made worse by subtropical highs and sinking air. Pressure belts shifting seasonally is related to the Sun’s solar declination and how sunlight hits the Earth. Upper Atmosphere Winds Reminder: The Troposphere is the closest part of the atmosphere to the Earth, and where we live. It’s followed by the Stratosphere, mesosphere, and thermosphere. Upper Troposphere: Winds in the upper troposphere are extremely fast, as there’s not as much friction (none of the air is touching the ground, or trees, or houses, etc.). Winds try to go to the poles but get redirected by Coriolis, making Westerlies, which are stronger in the winter because that’s when temperature gradients are the biggest. The thermal differences correspond to upper air height differences, and speeds go up with altitude as temperature differences make contours slope more steeply. (I’m being totally honest here, I have no Idea what the last sentence means, so unfortunately I won’t be able to translate it for you guys). Here’s another video: https://www.youtube.com/watch?v=r4wDsb7JYDs Polar Fronts and Jetstreams Strong boundaries between cold and warm air are called Polar Fronts, which mark the thermal shifts in the midlatitudes. In the upper troposhere are Polar jet streams, or really fast streams/rivers of air. Subtropical Jet streams near the Equator, on the other hand, move moisture and energy from the tropics to the poles. These winds are twice as strong in the winter as in the summer, again, because of the bigger temperature differences. Troughs and Ridges: Height contours wander as you go around the globe (what, do you expect air pressure to just walk in a straight line? It’s high, there’s no way that’s going to happen). Troughs are dips in air pressure while ridges are high pressure. Rossby Waves: These are the biggest atmospheric long waves, and each has it’s own wavelength and amplitude. There are 37 of them circling the globe at any given time, though there are more in the summer than in the winter. It makes sense, because the Earth is warmer in the summer, and will give off more longwave energy. They have preferred anchoring positions, but the Rossby waves still migrate Eastward. Rossby waves are extremely important in shifting energy north/south (meridional transport) and finding areas that are important for storm development. Once more time, here’s a video: https://www.youtube.com/watch?v=6vgvTeuoDWY Oceans have huge basins in them, and when water moves horizontally along the rims, that’s a current. They’re made by wind, but the water only goes at a 45 degree angle (down and to the right in the Northern Hemisphere), with the speed and direction shifting more toward the right as you get deeper. This is called the Ekman Spiral, started off by, again, the Coriolis Effect, and is basically nil at 100m deep, but currents have a big impact on the above atmosphere. A band director’s ‘one more time,’ actually: https://www.youtube.com/watch?v=zYms4lHpgLc North and south equatorial currents turn the water west to make the equatorial countercurrent. Because the water is going west from the Equator, western basin edges tend to be full of warm, poleward moving water for example, the Gulf Stream. The eastern edges of basins tend to be full of cold water going back to the equator. The air temperatures above the currents work with the water cold air above cold water, and warm air above warm water. The Gulf Stream moves 100 times as much water each minute as all the rivers in the world combined. Remember, though: West is Warm. Upwelling drags cold water up when offshore winds in coastal areas drag warm surface waters out to sea. It’s most obvious off the western coast of South America, where cold water upwelling helps make some of the worst desert conditions ever. How many videos will there be in this lecture?? https://www.youtube.com/watch?v=9peDRkO TLc Major Wind Systems: Monsoons are when each season, surface winds decide to turn around. They happen because of seasonal temperature differences between land and water. The East Asian monsoons are as such: cool months: dry offshore flow conditions; warm months: wet, onshore flow conditions. Orographic uplifting makes even more precipitation for areas around the Himalayas, which have some of the highest precipitation records anywhere. Yes, people, even worse than Alabama when it rains for a week straight, even if there were people swimming in a puddle outside my dorm. India has it worse. Foehn Winds are pronounced FOON, like the lady from the Doctor Who episode in which the Doctor nearly crashes a replica of the Titanic onto the Buckingham Palace. Anyways, Foon winds flow down the sides of mountains, and the air compresses due to, well, higher air pressure as altitude decreases. The air warms up remember Adiabatic Heating? Here it is again. Foehn winds are initiated when midlatitude cyclones pass by the southwest of the Alps. Chinooks are similar to Foehn winds, only they happen on the eastern side of the Rocky Mountains and happen when because of low pressure systems forming to the east of the mountains. Both Foehn and Chinooks are more common in winter than in summer. Santa Ana winds in California help spread wildfires and are common in transitional seasons particularly fall when there’s high pressure to the east. Katabatic Winds not only have a cool name and form by compression, but they originate when air is locally chilled over high elevations. As the air cools, it becomes denser and flows downhill. These are common in the Antarctica and Greenland icesheets. Katabatic winds are also called the Boras Winds of the Balkan Mountains (catchy, right?) and the Mistral Winds of France (not quite as catchy). And at long last, Pic from: https://www.youtube.com/watch?v=15JssBJf1xo 4/6 notes taken by Elle Gossman Major Wind Systems Temperature differences between the land and the sea result in air shifting toward the warmer area. Winds are named for their point of origin, so land breezes go from land to sea and sea breezes go sea to land. The thermal flow over the warmer surface causes air to rise, making a low pressure area, before the water vapor in the air condenses to make clouds and precipitation. In the day, land is hotter while at night, sea is hotter. Valley and Mountain breezes function on the same principle. The mountain facing the sun is nice and warm, while the shaded valley stays cool. A low in the day makes a valley breeze while the mountain breeze comes in at night. Remember, winds are named for where they come from. AirSea Interactions El Niño happens every 25 years, when the trade winds pushing equatorial waters westward aren’t as strong. There’ll be unusually warm waters in the Eastern Equatorial Pacific, resulting in more evaporation and lower air pressure. The cool waters in the east are replaced by warmer waters, which results in a reversal of walker circulation. As the warm waters go eastward, the air pressures above swap. Walker Circulation usually has air rising over the Western Pacific, while air sinks over the Eastern Pacific. The Southern Oscillation is linked to El Niño so strongly that they’ve simply become ENSO: El Niño/Southern Oscillation events.The shift in atmospheric pressures ends up messing with the weather across the world. The Pacific Decadal Oscillation is a pattern of atmospheric events over the Pacific that repeats every decade or so. There are 2 modes of surface water temperatures one is in the northwest and the other in the Eastern Tropical Pacific. The North Atlantic Oscillation (NAO) is in a positive phase when the pressure gradient is bigger than normal, and in a negative phase when the temperature gradient is smaller than normal. Air Masses and Fronts Air masses have the same temperature and humidity throughout, and affect really big areas. Fronts are where two different air masses meet each other and say hello. Here’s a video! https://www.youtube.com/watch?v=huKYKykjcm0 Formation of Air Masses: The places where air masses form are called source regions. Air masses have to stay there for a while to adopt the characteristics of the area. These are the different types: cA Continental Arctic Cold, dry air. It’s very Forms over high lat. of Asia, stable and has few clouds. North America, Greenland, Antarctica. cP Continental Polar Cold, dry, stable air with Forms over high lat. continental few clouds. interiors. Canada, Siberia mP Maritime Polar Cold, damp air with lots of Forms over high latitude oceans. clouds. Air is somewhat unstable. cT Continental Tropical Air is hot, dry, and very Forms over low latitude desert. unstable mT Maritime Tropical Warm, humid air Forms over subtropical oceans Here, watch another video: https://www.youtube.com/watch?v=Kmhizd4De2E Continental Polar air typically forms over places with lots of snow (high albedo) and not much insolation to make a cold, dry air mass. Continental Arctic is also in really cold temperatures, so the air doesn’t have much moisture. The boundary between Continental arctic and continental polar air masses is called the arctic front, and some people think the difference between the two air types is really minor. Maritime polar masses form over the North Pacific and are more moderate than continental polar masses. These affect North America mostly in the winter. They migrate east and cross over the west coast and the gulf of Alaska, but affect the East Coast as Northeasters (Northeasterly winds) and bringing snow and cold wind. Continental Tropical masses happen in summertime over hot, low latitude areas. The air is hot and dry, really unstable, and has little moisture. When there is moisture, the air freaks out and turns into a thunderstorm. Maritime Tropical air masses form over warm, tropical waters. They affect the US mostly in the summer, as with cT. Because they’ve got lots of moisture and are unstable, they make great opportunities for thunderstorms and heavy precipitation. Cough, Alabama, cough cough. Video no. 3! https://www.youtube.com/watch?v=ek9Jq9SKsE Fronts separate air masses and cause changes in humiditity and temperature. They come in occluded, stationary, warm, and cold types. Another video already? Odd. http://media.pearsoncmg.com/bc/bc_0media_geo/interactiveanimations/011_ColdWarmFronts_ HS_GG_Stu.html?cms#/WarmFronts A cold front is when a mass of cold air goes toward a warm air mass, and brings heavy precipitation and a temperature drop with it. A warm front is when a bunch of warm air goes toward a bunch of cold air. They end up with a bunch of warm, moist air over the cool, dry stuff. They don’t have many clouds, but they can have a little precipitation and shallow stratus clouds (they don’t go up much because of the stable air above them). Warm fronts bring frontal fogs. Stationary fronts just kind of sit there, though they may migrate. They’re just two air masses chillin’ out, maxin’, relaxin’ all cool, maybe shootin’ some bball outside of the school. When a couple of guys, who were up to no good, started making trouble in the neighborhood. I got in one little fight, and my mom got scared, said “You’re moving with your auntie and uncle in BelAir. Back to the notes. Occluded fronts happen when two fronts meet. The warm air mass between them is shoved upward. Cold type occlusion is usually in the eastern half of the continent, while warm type occlusion typically happens on the west side of the continent. http://audiofrost.com/2015/08/13/willsmithtoproducefreshprinceofbelairreboot/
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