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Lecture

EESA09 WIND NOTES.docx


Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin

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EESA09 WIND NOTES
Lecture 1: Introduction to Wind
1.1 Mythological and Cultural Winds
- Wind played key role in humanity‟s mythology and cultural development
- Aeolus (Greek god of wind), Feng Po Po (Chinese goddess of wind), Haya-ji (Japanese
god of wind), Nilch‟I (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
- Earth‟s 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 CO2 and methane (CH4) due to volcanic 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 O2) forms appeared and flourished
o Atmosphere has been relatively constant; some variations in trace gases like CO2
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% O2 optimal for aerobic life on Earth; Mars and Venus are in static
equil. with CO2 and CH4
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

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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 Earth‟s surface and re-radiate the energy back to the
surface, causing surface to be warmer than usual (on avg. 33°C warmer)
o Water vapor (H2O), CO2, methane (CH4), nitrous oxide (N2O), ozone (O3),
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 sun‟s radiation
o Temperature ↓ by 6.5°C 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

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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 16th century
o Liquid-in-glass thermometer
Temperature changes accessed using expansion of fluid (mercury, alcohol)
Captain Robert Fitzroy, 19th 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
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