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EESA09H3 (185)


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University of Toronto Scarborough
Environmental Science
Tanzina Mohsin

1 EESA09 WIND NOTES Lecture 1: Introduction to Wind 1.1 Mythological and Cultural Winds - Wind played key role in humanitys mythology and cultural development - Aeolus (Greek god of wind), Feng Po Po (Chinese goddess of wind), Haya-ji (Japanese god of wind), NilchI (Navajo holy wind, North American Indian) - In Hindu and Buddhist religions, wind viewed as the nature or state of a god - Wind is one of the five great elements - Wind also played metaphorical roles in literature 1.2 Atmospheric Primer: The History of Wind - Earths atmosphere existed for 4.6 billion years - Composition of atmosphere not constant; variations in atmospheric constituents occurred due to three main controls: geological, biological, and anthropogenic Geological Control: o Early atmosphere composed of CO and me2hane (CH ) due to v4lcanic emissions o Life appeared 3.8 billion years ago; anaerobic (not needing oxygen)flourished in this environment Age of Bacteria Biological Control: o 2.3 billion years ago, oxygen made appearance in atmosphere and stabilized at 21% aerobic life (life needing O )2forms appeared and flourished o Atmosphere has been relatively constant; some variations in trace gases like CO 2 played key role in determining thermal conditions of earth o Gaia Hypothesis by James Lovelock: life modifies the environment to best suit itself atmospheric constituents have been controlled by life to optimize conditions for life 21% O op2imal for aerobic life on Earth; Mars and Venus are in static equil. with CO and CH 2 4 Anthropogenic Control: o Solar energy converted to plant material o Decaying plants not fully oxidized o Converted to coal (& oil) under geologic pressure & stored for millions of years o Rapid release of this energy causes many air quality problems today (smog, acid rain, global warming) o Story of coal represents first major anthropogentic modification of atmosphere o Atmosphere become a modern dumping ground Fossil fuels emissions linked to acid rain, urban air quality, urban heat island, global warming Other industrial emissions linked to ozone hole 1.3 The Basics Composition - Air mainly gas phase, liquid phase in clouds, solid phase as particulate matter - Gas phase constituents of air are permanent and variable 2 o Permanent gases are in dynamic equilibrium (both creation and destruction) o Variable gases referred to as greenhouse gases - Greenhouse gas is an atmospheric constituent that traps outgoing terrestrial radiation o Intercept radiation from Earths surface and re-radiate the energy back to the surface, causing surface to be warmer than usual (on avg. 33C warmer) o Water vapor (H O),2CO , met2ane (CH ), nit4ous oxide (N O), oz2ne (O ), 3 chlorofluorocarbons (CFCs) o Natural Greenhouse Effect - Anthropogenic emissions of greenhouse gases trap excess heat causing the Enhanced Greenhouse Effect Global Warming Clouds - Cloud types named using five root morphs: strato, cumulo, cirro, nimbo, and alto o Strato layered clouds, greater horizontal extent than vertical extent o Cumulo puffy clouds, similar horizontal and vertical o Nimbo rain clouds o Alto mid level clouds, between 2 km and 7 km o Cirro high level clouds, above 7 km - Types of clouds o Stratus low level, layer cloud o Altostratus mid level, layer cloud o Cirrostratus high level, layer cloud o Nimbostratus layer cloud that produces rain, darker than stratus and greater vertical extent o Cumulus low level puffy cloud o Stratocumulus a layer of puffy clouds o Cumulonimbus towering cloud extending through troposphere which produces intense precipitation including hail o Altocumulus mid level puffy cloud o Cirrocumulus high level puffy cloud o Cirrus wispy high level cloud Atmospheric Layers - Atmosphere divided into 4 vertical levels Troposphere: o Extends approx. 11 km, varying 13 km at equator and 8 km at poles o Well mixed vertically o Virtually all weather occurs here o 75% of atmosphere mass o Tropopause is isothermal region between troposphere and stratosphere o Warming occurs at the surface from suns radiation o Temperature by 6.5C per km Stratosphere: o Extends approx. 11 km to 50 km o Very stable, very little vertical mixing o Temperature with height o Warming due to conversion of incoming solar radiation into kinetic energy of motion via a layer of ozone; related to ozone hole issue 3 Mesosphere: o Extends 50 to 85 km o Well mixed layer, less stable than stratosphere o Temperature with height Thermosphere: o Extends above 85 km o Temperature with height o Incoming solar radiation absorbed by molecular oxygen and energy is converted to kinetic energy of motion o Temperature is warm; but one will not feel warm at this level as air has very low density at this level, thus low transference of heat What is Wind? - Cannot be seen directly but can be inferred by its effects such as the movement of objects and causing objects to become airborne - Can be felt and heard - Results from differences in air pressure, either vertical or horizontal, producing a pressure gradient - Air tends to move from high pressure to low pressure, the force that causes this is the pressure gradient force Observing the Atmosphere - The following are measured: temperature, pressure, humidity, wind speed and direction, precipitation, sky condition, and composition (air quality) Temperature: o Thermometer invented in late 16 century o Liquid-in-glass thermometer Temperature changes accessethusing expansion of fluid (mercury, alcohol) Captain Robert Fitzroy, 19 century standardized thermometer o Electrical thermometer Electrical resistance a function of temperature o Bimetallic thermometer Two metals welded together, thermal expansion different for both so they bend in different directions depending if warm or cool Pressure: o Barometer invented by Torricelli in 1643 o Mercury Pressure changes assessed using the movement of mercury in a column o Aneroid barometer Pressure measured by changes in volume of a partially evacuated box Commonly used in aircraft, known as altimeter Humidity: o Hygrometer Invented in 1780 Expansion and contraction of material due to changes in humidity Hair typically used 4 o Psychrometer Measures two temperatures, the dry bulb temperature and the wet bulb temperature Dry bulb temperature is the ambient temperature, usually measured by thermometer Wet bulb temperature is the lowest temperature attainable due to the cooling of air due to evaporation of water until saturation occurs (max. amount of water vapor in air before condensation occurs) If air is dry (not close to saturation) the wet bulb temp. will be well below the dry bulb temp. If air is saturated (high humidity) no evaporation can take place and the wet bulb and dry bulb temperatures are the same The larger the difference between the two bulbs, the dryer the air Wind Speed and Direction: o Anemometer o Series of small cups which catch the wind and rotate o Faster the rotation, the water the wind o Weather vane indicates wind direction Precipitation: o Measured using rain and snow gauges o Collect failing precipitation 1.4 Current Challenges - Mitigating (justifying) the destruction of wind phenomena, tornadoes, hurricanes, ice storms - Harnessing wind for power - Climatic change/global warming 1.5 Special Topic: Rising air produces clouds - Warm air rises and cool air sinks - Cooling leads to condensation Lecture 2: Global Wind Circulation 2.1 What is Wind? - Cannot be seen directly but can be inferred by its effects such as the movement of objects and causing objects to become airborne - Can be felt and heard - Results from differences in air pressure, either vertical or horizontal, producing a pressure gradient - Air tends to move from high pressure to low pressure, the force that causes this is the pressure gradient force (PGF) - Coriolis Force (CF), fictitious force resulting from Earths rotation, acts on wind o Gustave de Corio
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