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Atmosphere And Climate Atmosphere • Invisible layer of gases that surround the earth – 78% nitrogen – 21% oxygen – 0-4% water vapor (major non anthropogenic greenhouse gas) – 1% carbon dioxide, methane, nitrous oxide, ozone • Atmosphere becomes less dense as you move upwards into space Carbon Dioxide • -produced by cellular respiration and organic decay • **major greenhouse gas • Avg time a molecule stays in atmosphere=100 yrs. • Volume has increased ~25% in last 300 yrs. Due to burning of fossil fuels and deforestation Methane • Major greenhouse gas • Since 1750 has increased 150% due to : – Use of fossil fuels – Coal mining – Landfills – Grazers (cattle) **stays about 10 yrs in atmosphere Nitrous Oxide • Contributor to greenhouse effect • Increasing about .3% per year due to: – Burning of fossil fuels – Fertilizers – Burning biomass – Deforestation **lasts about 170 yrs in atmosphere Atmosphere Origin • Gases were released from the planet itself • Functions: – Protects earth from uv rays, x-rays, cosmic rays – Allows visible light and infrared (heat) to penetrate, warming the earth – 2.3-2.7 billion years ago evolution of photosynthetic organisms Layers of the Atmosphere • • • • • • Troposphere Stratosphere Mesosphere Thermosphere (Ionosphere) Exosphere Memory technique: Troy smiled more than Ed Layers of the Atmosphere Layers of the Atmosphere Troposphere • • • • 0-7 miles (0-11km) above surface 75% of atmosphere mass Temp. decreases with increasing altitude Weather occurs in this layer Stratosphere • Extends 12-50 km up • Temperature increases with altitude because of heat absorption by ozone • **contains ozone layer** Mesosphere • 51-80 km • Lowest temperature in atmosphere (-138oC) • Meteors burn up here Thermosphere (Ionosphere) • 81-120 km • Temp. rises steadily with increasing altitude due to gamma rays, x-rays, and uv rays • Gases absorb x-rays and short wave uv radiation • Aurora borealis and aurora australis (southern hemisphere) occur here Aurora borealis-sept-oct, marchapril Heat Transfer • Heat always move from a warmer substance to something that is cooler • Heat moves in 3 ways: – Radiation – Conduction – Convection Radiation • Transfer of energy through space as waves or particles (no direct contact between objects) – Ex. When your car door handle gets hot on a sunny day – Dark objects absorb more radiation than light objects Conduction • Transfer of heat between 2 objects that are in contact with each other (when molecules collide) – Ex. When your hand touches the hot car handle Convection • The transfer of heat by the movements of the currents in gases and liquids • Related to DENSITY – Convection currents: warm air is less dense than cooler air – Convection currents cause winds and move heat through the atmosphere Heat Transfer Weather vs. Climate • Weather-day to day • Climate-total of all weather occurring a long period of time (includes avg temp and avg precipitation) Factors that Influence Climate • Air mass-a large body of air that has similar temps and moisture • Can be equatorial, tropical, polar, arctic, continental, or marine Factors that Influence Climate • Air pressure-gravity on an air mass, measured in millibars, inches of mercury, hectopascals (hPa), decreases with altitude low pressure=usually cloudy and stormy weather high pressure=usually fair weather Factors that Influence Climate • Albedo-reflectivity – oceans=low albedo – Land masses=moderate – Snow & ice=high More ice=more cooling (positive feedback loop) Factors that Influence Climate • Altitude-for every 1000 ft (300m) rise in elevation, there is a 3F (1.5 C) drop in temp – Every 300 ft (90m) rise in elevation=62 mile (100km) north latitude Factors that Influence Climateangle of the sunlight Factors that Influence ClimateCarbon Cycle • Consumption of carbon results in cooling • The production of carbon results in warming Factors that Influence Climate • • • • Clouds Fronts Greenhouse effect Convection currents (atmosphere & ocean) • Land changes-urbanization/deforestation • Landmass distribution • Latitude Factors that Influence Climate • Humidity-water vapor a greenhouse gas • Mountain ranges • Plate tectonics and volcanoes: plate instability=more volcanic activity • Volcanoes-can cause tropospheric cooling when a lot of ash is ejected into atmosphere, also increased amount of ash in oceans, increases biotic activity, lowering carbon dioxide content of water, which leads to cooling Factors that Influence Climate • Solar output-sunspots=decrease in solar radiation, solar flare=increased radiation • Pollution • Precession (earth wobbles on its axis and its orientation in space (tilt) can change periodically) • Wind patterns (global air circulation) Major Climatic Periods • Pleistocene Ice Age (2,000,000 B.C.E to 12,000 B.C.E) – Large glaciers covered much of N. America, Europe, and Asia – Average temps. 7-9 F (4-5 C) colder than today Major Climatic Periods • 12,000 B.C.E to 3000 B.C.E – Gradual period of warming and glacial retreat – Brief cooling period occurred between 10,0008500 B.C.E perhaps caused by a large influx of fresh water shifting ocean currents – By 3000 B.C.E average global temps = 2-4 F (1-2 C) warmer than today – Known as the Climatic Optimum (many great ancient civilizations flourished during this time) Major Climatic Periods • 3000 B.C.E. to 750 B.C.E – Period of overall cooling – Glaciers grew and sea level dropped Major Climatic Periods • 750 B.C.E to 900 C.E – In general a warming trend except • Roman Empire (150 B.C. E to 300 C.E) saw a cooling trend when the Nile River and Black Sea would freeze Major Climatic Periods • 900 C.E to 1200 C.E • Little Climatic Optimum – A warming period – Vikings established settlements on Greenland and Iceland – Records of flood, droughts, and extreme seasonal fluctuations Major Climatic Periods • 1550 C.E to 1850 C.E. • Little Ice Age • Average temp. of northern hemisphere= 2F (1 C) colder than today Major Climatic Periods • 1850 C.E to present • General period of warming Atmospheric Dynamics • Atmospheric circulation – Transfers heat from equator to the poles (warm air near equator rises, then cools and sinks again) – Moderates earth’s temperature – The atmosphere circulation AND the ocean currents determine climate • Climate=avg. temp. and avg. precipitation Surface Winds • Influenced by: – Temperature and pressure differences (gradients) • Caused by: – Uneven heating of earth’s surface – Seasons – Coriolis Effect – Amount of solar radiation reaching earth – Convection cells in the ocean Differences in Atmospheric Pressure • Winds blow from high pressure to low pressure (the greater the difference between the high and low, the stronger the wind Earth’s Rotation • Earth rotates from west to east – Coriolis Effect: earth’s rotation causes the winds to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere Three Prevailing Winds • Winds are named for the direction they come FROM – Polar easterlies (north and south poles) – Westerlies (mid-latitudes) – Trade winds (tropics) Three Prevailing Winds 3 Types of Air Circulation Cells Associated with Latitude • Hadley-tropics • Ferrel-temperate regions • Polar Hadley Air Circulation Cells • Warm air rises at the equator and moves toward the temperate latitudes with air there cooling and sinking to return to the equator • Equatorial regions are characterized by high humidity, high clouds, and heavy rains (tropical rainforest) • Subtropical regions characterized by low relative humidity, few clouds, high ocean evaporation (deserts, savanna) Ferrel Air Circulation Cells • Develop between 30-60 north and south latitude • Climate goverend by both tropical and polar air masses • Defined seasons with strong annual cyles of temp and precip. • Broadleaf deciduous and taiga Polar Air Circulation Cells • Originate as icy-cold, dry dense air that descends from the troposphere to the ground • Sinking air suppresses precipitation, hence the polar regions are deserts • Tundra and some taiga The Ocean • Salt water covers ¾ of the earth’s surface (continuous body of water, but divided into 4 sections-Pacific, Atlantic, Indian, Arctic) – Pacific covers 1/3 of earth and contains more than ½ of earth’s water Ocean Currents • Caused by prevailing winds – Gyres: circular ocean currents • Influenced by Coriolis Effect • Varying density-warm water is less dense than cold water Gyres Weather • Short term properties of the troposphere such as: – Temperature – Pressure – Humidity – Precipitation – Cloud cover – Wind direction and speed Fronts • Boundary between 2 air masses with different temps and densities – Warm front – Cold front Warm Front • Boundary between an advancing warm air mass and the cooler one it’s replacing • Warm air is less dense, so it rises up over the mass of cooler air • First signs: high, wispy clouds – A moist warm front can bring days of cloudy skies and drizzle Warm Front Warm Front Warm Front Cold Front • Leading edge of an advancing mass of cold air • Wedges underneath (more dense) the warmer air mass • Produces thunderstorms Cold Front Cold Front Cold Front Air Pressure • Caused by tiny molecules bouncing off of each other; affected by gravity – Air pressure at the earth’s surface is greatest because of the weight of all of the other air particles being pulled by gravity • High pressure • Low pressure High Pressure • High, dry, cool • Winds are clockwise and out • Usually associated with fair weather Low Pressure • Low, moist warm • Winds move counterclockwise and inward • Usually associated with stormy weather High Pressure/Low Pressure Extreme Weather • Tornados (form over land)-each year more than 800 touch down in the US • Tropical Cyclones (form over water) – Form over Atlantic Ocean=hurricanes – Form over Pacific Ocean=typhoons • The warmer the water where the storm tracks, the more energy the storm has and the more damaging it will be • Monsoons Hurricane/Typhoon Hurricanes • Most severe weather phenomenon • Katrina=$75 billion in damage and 1,830 deaths • Separate thunderstorms that develop over tropical oceans, coriolis effect initiates cyclonic flow • Can be hundreds of kilometers Typhoons/Hurricanes • Negative Impacts-deaths, property damage • Ecological Benefits: – Flushes out excessive nutrients, dead and rotting sea grass from coastal bays and marshes. This flushing out in turn: • Reduced brown tides • Increased growth of sea grasses • Increased the number of shrimp, crabs, fish Tornadoes • Swirling masses of air with wind speeds close to 300 mph • Tornado alley in the U.S • Hundreds of meters, one storm (not many) Tornado Monsoons • Very strong winds that change direction with season (blow from land to sea in winter and sea toward land in summer) • India (hot dry winters), wet heavy rains in summer, because the monsoons bring moisture from the ocean • Farmers rely on this water for irrigation and a large amount of India’s power is generated by water received from monsoons El Nińo-Southern Oscillation (ENSO) • Air pressure patterns in south Pacific reverse direction, so trade winds can weaken or even reverse (so ocean water piles up in S. America pushing thermocline deeper and causing many changes) • Prevailing westerly winds weaken or cease • Surface water along the S. and N. American coasts becomes warmer • Suppresses upwellings(colder, more oxygenated water that cycle nutrients) El Nińo-Southern Oscillation • Productivity decreases, sharp decline in some fish populations • Can trigger extreme weather changes (mild winters on east coast, stronger storms in the west) • Shift in prevailing rain pattern La Nińa • Cooling of ocean surface water • Shifts prevailing rain patterns • More hurricanes b/c of temperature increase in SE U.S • Heavier than normal monsoons in India and SE Asia • Almost causes the opposite effect of El Nino to the U.S.: – Winter temps. warmer than usual in SE U.S – Cooler than normal in NW El Nińo-Southern Oscillation/ La Nińa Ozone Layer • Located in Stratosphere • O2 is continuously converted into O3 (ozone) by uv radiation • Keeps 95% of harmful uv rays from reaching the earth • Provides a thermal cap so warm, churning gases do not leave the troposphere Microclimates • Local climatic conditions • Caused by: – Mountains – Cities – Land to ocean interactions Microclimates-Mountains • (Seattle) Moist air blowing inland from the ocean is forced to rise up over the mountains • Rising air expands, cools, and condenses (RECC) so precipitation occurs • As the drier air mass flows down the other side of the mountain it draws moisture from plants and soil • Rain Shadow Effect-the term for the low precipitation and semi-arid conditions on the leeward side of mountains Rise, Expand, Cool, Condense Microclimates-Mountains Microclimates-Mountains Microclimates-Cities • Concrete, asphalt, brick, and building materials absorb and hold heat and block wind flow • Haze and smog from pollutants released from vehicles create higher temps. Microclimates-Cities Microclimates-Land-Ocean Interactions • Ocean to land breezes during the day (sea breezes) • Land to ocean breezes at night (land breezes) Sea Breeze Land Breeze Other wind types • Anabatic winds- a warm wind which blows up a steep slope or mountain side, driven by heating of the slope through insolation, • Katabatic winds- down-slope winds, frequently produced at night by the opposite effect, the air near to the ground losing heat to it faster than air at a similar altitude over adjacent low-lying land.