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Unit 2: Air Part 1: Atmosphere & Climate Thank God men cannot fly, and lay waste the sky as well as the earth. - Henry David Thoreau 1 KEY IDEAS ► Earth is characterized by patterns of temperatures and precipitation. ► These patterns arise from the circulation of air and ocean water, which is ultimately driven by unequal heating of Earth by the Sun, the rotation of Earth, and Earth’s geographic features. ► Geographic variations in temperature and precipitation have led to the development of distinct terrestrial biomes, which are defines by their unique plant communities, and distinct aquatic biomes. ATMOSPHERE AND CLIMATE ► Weather - A description of short-term physical conditions of the atmosphere in a local area. An afternoon thunderstorm ► Climate - A description of the long-term weather pattern in a particular area. Temperature Humidity Wind Rainfall 3 HOW DOES CLIMATE & WEATHER AFFECT LIFE? Regional differences in temperature and precipitation collectively help determine which organisms can survive in each region. To understand these differences, we need to understand the processes that effect the distribution of heat and precipitation. These processes include: Unequal heating of Earth by the Sun Atmospheric Convection Currents Rotation and Revolution of Earth on Tilted Axis Ocean Currents The Atmosphere ► The atmosphere is a layer of gasses surrounding the Earth consisting of 5 layers If the Earth were the size of an apple, the atmosphere would be the skin. 5 Layers of the Atmosphere 6 Layers of the Atmosphere ► Troposphere (0 km to 16 km; 10 miles) Largest and lowest part of atmosphere. Weather occurs in this layer. Carbon dioxide is trapped in this layer, forming the basis of the greenhouse effect and global warming. Most dense layer; Most of the gas (Nitrogen, Oxygen, Water Vapor) found here. Large amount of circulation and mixing Temperature decreases as altitude increases. 7 Layers of the Atmosphere ► Stratosphere (16-50km; 10-31 miles) Very stable, calm layer of the atmosphere; Less dense due to distance from Earth’s gravitational pull. ►Used by aircraft. Contains the ozone layer (Made of Ozone molecules); Incoming UV rays reach higher altitudes first, thus the higher altitudes are warmer. (Temp increases as altitude increases) A Word about Ozone (O3) ► Ozone is a pale blue gas composed of 3 oxygen molecules. ► The layer of ozone absorbs MOST of the Sun’s ultraviolet-B (UV-B) radiation and ALL of its ultraviolet-C (UV-C) radiation. UV radiation can cause DNA damage and cancer in organisms, so the ozone layer provides a critical shield of protection for life on Earth. Layers of the Atmosphere ► ► MESOSPHERE: (~60-100 km) THERMOSPHERE: (~100 km-600 km) Blocks harmful X-ray & UV radiation Contains charged gas molecules that, when hit by solar energy, begin to glow and produce light The interaction is driven by magnetic forces at the poles. ► EXOSPHERE ► Due to weaker gravitational pull on molecules at these altitudes, the pressure and density in each of these layers decrease as it extends into space. ► Aurora Borealis (Northern Lights) ► Aurora Australis (Southern Lights) THE EARTH & THE SUN ► The Sun has the greatest influence on Earth Affects its movement Determines day-night and seasonal cycles Driving climatic systems and long term climate cycles Provides energy for most life on Earth ►Also plays part in TIDAL movement by modifying the effect of the Moon to produce monthly variation in the tidal range. The Sun ► The Sun emits various types of radiation, most of which is absorbed by the ATMOSPHERE. ► The radiation that reaches the surface: Visible Light: Critical to producers Infrared Radiation: Ultraviolet ► Intensity of solar radiation is not uniform around the Earth, thus…. The Earth & The Sun ► ..THE UNEVEN HEATING EFFECT, TOGETHER WITH THE EARTH’S ROTATION, PRODUCE THE GLOBAL PATTERNS OF WIND AND OCEAN CIRCULATION THAT PROFOUNDLY INFLUENCE THE EARTH’S CLIMATE!! THE EARTH & THE SUN ► SOLAR YEAR: Earth takes 365.25 days to orbit around the Sun (Revolve) ► EARTH DAY: Earth spins (Rotation) on its axis once every 23 hours 56 minutes 4.09 seconds) ► Earth does not spin upright; it has a 23.5 degree tilt. The tilt ALWAYS faces the SAME way= Results in seasonal changes in sunlight and weather. Sun Angle Controls Sunlight Intensity ►At low angles (Oblique), sunlight spreads over much larger areas & thus heats less effectively. ►At low angles, sunlight reflects from water & ice more efficiently. Garrison, 2005 Poleward Heat Transport to Balance Unequal Heating ►Equator would be hotter & poles would be much colder without this transport. ►Transport by winds & ocean currents. Garrison, 2005 ► Visible Solar Radiation light is energy waves that we can see as color. These pass through the atmosphere. ► Ultraviolet light is energy waves that we cannot see but can cause sun burns and cancer. These are absorbed by ozone in the stratosphere. ► Infrared radiation is the energy of the sun that we feel as heat. This is absorbed by carbon dioxide and water in the troposphere. 19 Energy and the Greenhouse Effect ► Solar Radiation Of solar energy reaching outer atmosphere: ►25% reflected ►25% absorbed ►50% reaches earth’s surface Of the solar energy that reaches the surface, much is reflected: ►Fresh clean snow ►Dark soil ►Net average of earth 90% 3% 30% 20 EARTH’S TILT & THE SEASONS ► Because of the 23.5 degree tilt of Earth on it’s axis, most regions of the world experience seasonal changes in temperature and precipitation. When the Northern Hemisphere is tilted toward the Sun, the Southern Hemisphere is tilted away from the Sun. The Sun’s rays strike the equator directly 2x a year: the March equinox and the September equinox. ► On these days, virtually all regions experience 12 hours of daylight and 12 hours of darkness. ► For the 6 months between March and September equinoxes, the N.H. tilts toward the Sun (more daylight hours than darkness) EARTH’S TILT & THE SEASONS ► On June 20 or 21 (June Solstice), the Sun is directly above the Tropic of Cancer (23.5 degrees N), the N.H. experiences more daylight hours than on any other day of the year. ► For the 6 months between September and March, the N.H. tilts away from the Sun and experiences fewer hours of daylight than darkness. ► On December 21 or 22 (December Solstice), the Sun is directly over the Tropic of Capricorn (23.5 degrees South). On this day, the N.H. experiences its shortest daylight period of the year. EARTH’S TILT & THE SEASONS ► In summary, Earth’s tilt on its axis produces predictable seasons. Solar Radiation 25 KEY CONCEPT UNEQUAL HEATING OF THE EARTH Caused by: 1. Variation in the angel at which Sun’s rays strike Earth ► -The tropics (near equator) hit at perpendicular angle. -Mid-latitude and polar regions are hit at more oblique angles. *As a result, the Sun’s rays travel a shorter distance through the atmosphere to reach Earth’s surface in the tropics. In other words, at high latitudes, sunlight must pass through more atmosphere, and thus lose more of its energy. KEY CONCEPT ► ► UNEQUAL HEATING OF EARTH Caused by: 2. Variation of amount of SURFACE AREA over which the Sun’s rays are distributed. -The perpendicular angle of rays in the tropics cause solar energy to be distributed over a smaller surface area there than at higher latitudes. - Shine light on ball…you get a focused orb of light. -Shine light on top of ball at oblique angel..you get an oval pool of dimmer light over a larger area. KEY CONCEPT ► UNEQUAL HEATING OF EARTH Caused by: 3. Certain areas of Earth reflect more solar energy than others *The percentage of incoming sunlight that is reflected from a surface is called its ALBEDO -The higher the albedo of a surface, the more solar energy it reflects, and the less it absorbs. -A white surface has a higher albedo than a black surface, so it tends to stay cooler. How Uneven Heating Drives Circulation ► The amount of heat in the atmosphere directly affects the movement of water. ► Warm air containing evaporated water rises higher into the atmosphere. Warm air is less dense than cool air. ► As warm air rises, heat is released into the atmosphere and the water vapor condenses. The condensed water then falls as rain or snow. 29 PROPERTIES OF AIR ► 1. 2. 3. 4. 4 Properties of Air Determine How it Moves: Density Vapor Capacity Adiabatic Heating or Cooling Latent Heat Release 1. DENSITY OF AIR & 2. VAPOR CAPACITY ► Less dense air RISES, dense air SINKS… ► Warm air has a lower density than cold air Therefore, warm air rises Also, hot summer days=high humidity ► The warm air contains a lot of water ► Saturation Point: Max. amount of water that can be in the air at a given temperature. When air temp. falls, its saturation point decreases & water vapor condenses into liquid water, clouds form, and precipitation occurs. 3. ADIABATIC HEATING & COOLING ► As air rises higher in the atmosphere, the pressure on it decreases. The lower pressure allows the rising air to expand in volume, and this expansion lowers the temperature of the air ► Called ADIABATIC COOLING When air sinks towards the Earth, the pressure on it increases. The higher pressure forces the air to decrease in volume, and this decrease raises the temperature of the air ► Called ADIABATIC HEATING 4. LATENT HEAT RELEASE ► =The production of heat when water vapor condenses from a gas to a liquid. ► When water vapor in the atmosphere condenses into liquid form, energy is released (LATENT HEAT RELEASE) Explains how whenever water vapor in the atmosphere condenses, the air will become warmer and this warm air will rise. Convection Currents 34 Atmospheric Convection Currents ► A.C.C.= Global patterns of air movement initiated by unequal heating of Earth. ► Hadley Cells: The convection currents that cycle between the equator and 30 degrees N and S. Solar energy warms humid air in the tropics. This warm air rises and eventually cools below its saturation point. The vapor condenses into clouds and precipitation. The now dry air sinks to Earth’s surface at 30 degrees N and S. As the air descends, it is warmed by adiabatic heating. This descent of hot, dry air causes desert environments to develop at those latitudes. HADLEY CELLS INTERTROPICAL CONVERGENCE ZONE ► Intertropical Convergence Zone (ITCZ) The area of Earth that receives the most intense sunlight, where the ascending branches of the 2 Hadley cells converge. It is amplified by dense clouds and intense thunderstorm activity. POLAR CELLS ► Similar to Hadley Cells, the Polar Cells are convection currents that are formed by air that rises at 60 degrees N and S and sinks at the poles (90 degrees N and S). ► Between Hadley Cells & Polar Cells lies a 3rd area of circulation, Ferrell Cells. Not convection cells; movement driven by circulation of neighboring cells. GLOBAL AIR CIRCULATION RESULTS OF GLOBAL AIR CIRCULATION Distributes warm air away from the tropics and cold air away form the poles Allows for a wide range of warm and cold air currents to circulate between 30 and 60 degrees. Collectively, these convection currents slowly move the warm air of the tropics toward the mid-latitude and polar regions. This pattern of air circulation is largely responsible for the locations of rainforests, deserts, and grasslands on Earth. Earth’s Rotation & Coriolis Effect ► Rotation of Earth has important climatic influence, particularly on the Prevailing Winds. As Earth rotates, its surface moves much faster at the equator than at other regions. ► Imagine standing still at the equator as Earth rotates Given that a single rotation is 24 hours, you would be traveling at much faster speed at the equator than at the poles. ► The faster rotation speeds at the equator cause a deflection of objects that are moving directly north or south. The deflection of an object’s path due to Earth’s rotation is called the CORIOLIS EFFECT CORIOLIS EFFECT ► Massachusetts Institute of Tech (MIT) http://mit.tv/z79Q8o ► The prevailing wind systems of the world are produced by a combination of atmospheric convection currents and the Coriolis Effect If Earth did not rotate, the air within each convection cell would simply move directly North or South and cycle back again. Summary ► Simply stated, the atmospheric convection currents of tropical and polar latitudes, the mixing of air currents in the mid-latitudes, and the Coriolis effect cause the prevailing wind patterns that occur worldwide, although local features, such as mountain ranges, can alter wind directions. OCEAN CURRENTS ► Ocean currents are driven by a combo of temperature, gravity, prevailing winds, the Coriolis Effect, and the locations of continents. Ocean Currents ► As we have seen, the tropics receive the most direct sunlight throughout the year, and tropical waters are thus generally warm. ► Warm water, like warm air, expands and rises. This process raises the tropical water surface about 8cm higher in elevation than mid-latitude waters. ► This slight slope is enough for the force of gravity to make water flow away from the equator. Ocean Currents: GYRES ► Large-scale patterns of water circulation that redistribute heat in the ocean Cold water from polar regions moves along the west coasts of continents, and the transport of cool air from above these waters causes cooler temperatures on land. ► Global prevailing wind patterns play a major role in determining the direction in which ocean surface water moves away from the equator. In the N.H., the trade winds near the equator push water from the northeast to the southwest and the Coriolis effect deflects this wind-driven current so that water actually moves from east to west. ► The overall effect: Ocean SURFACE currents rotate in a clockwise direction in the N.H. & in a CCW direction in the S.H. Ocean Currents: UPWELLING ► These explain why some regions of ocean support highly productive ecosystems. ► Along west coasts of most continents, the surface currents diverge and cause deeper waters to rise and replace the water that has moved away. This upward movement of water to the surface is called Upwelling. ► The deep waters bring with them nutrients from the ocean bottom that support large populations of producers, which support large populations of fish. Ocean Currents: THERMOHALINES ► Thermohaline Circulation: Drives the mixing of surface water and deep water. Crucial to moving heat and nutrients around the globe. Driven by surface water that contain unusually large amounts of salt. 1. Warm water flows from Gulf of Mexico to the North Atlantic where some of it freezes and evaporates ► 2. The remaining water, now saltier and denser, sinks to the ocean bottom ► 3. The cold water travels along the ocean floor, connecting the world’s oceans. ► 4. The cold, deep water eventually rises to the surface and circulates back to the North Atlantic. ► Ocean Currents: HEAT TRANSPORT ► Ocean currents can affect the temperature of nearby landmasses. ► Ex: The ocean current known as the Gulf Stream originates in the tropics near the Gulf of Mexico and flows NE across the Atlantic toward Europe. As it moves warm waters north, the stream brings large amounts of heat energy to cooler regions, moderating temps in latitudes that otherwise would be much colder. Concern ► One major concern about global warming is that increase air temperatures could accelerate the melting of glaciers, which could make the waters of the North Atlantic less salty and thus less likely to sink. ► Such a change could potentially shut down thermohaline circulation and stop the transport of warm water to Western Europe, making it a much colder place. ALMOST DONE!! El Nino-Southern Oscillation ► Earth’s atmosphere and ocean interact in complex ways. ► Periodically (every 3 to 7 years), these interactions cause surface currents in the tropical Pacific Ocean to reverse direction. First, the trade winds near South America weaken, allowing warm equatorial water from the western Pacific to move eastward toward the west coast of South America. The movement of warm water and air toward South America suppresses upwelling off the coast of Peru and decreases productivity there, reducing fish populations near the coast. El Nino-Southern Oscillation phenomenon is called El Nino (“the baby boy”) because it often begins around the December 25 Christmas holiday. ► El Nino can last from a few weeks to a few years. These periodic changes in wind and ocean currents are collectively called the El NinoSouthern Oscillation (ENSO) ► Globally, the impact of ENSO includes cooler and wetter conditions in the southeastern US and unusually dry weather in southern Africa and Southeast Asia. ► This Rain Shadows ► ► ► Air moving inland from the ocean often contains a large amount of water vapor. This air meets the windward side of a mountain range (the side facing the wind), it rises and begins to experience adiabatic cooling. Because water vapor condenses as air cools, clouds form and precipitation falls. As is the case with Hadley cells, this condensation causes latent heat release, which helps to accelerate the upward movement of the air. Thus, the presence of the mountain range causes large amounts of precipitation to fall on its windward side. The cold, dry air then travels to the other side of the mountain range (leeward side), where it descends and experiences higher pressures, which cause adiabatic heating. RAIN SHADOWS This now warm, dry air produces arid conditions on the leeward side of the range forming a region called a RAIN SHADOW. ► It is common to see lush vegetation on the windward side of a mountain range and very dry conditions on the leeward side.