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Chapter 1 Introduction Elements of Weather & Climate Composition of the Atmosphere Thermal Structure of the Atmosphere. Basic Elements of Weather & Climate. Temperature Humidity Clouds Precipitation Air Pressure Wind. Hypothetical Winter Weather. - PowerPoint PPT Presentation
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Chapter 1Introduction
Elements of Weather & Climate
Composition of the Atmosphere
Thermal Structure of the Atmosphere
What’s portrayed:
•Temperature
•Precipitation
•Cloud cover
•Air pressure (crudely only)
Also important:
•Wind
•Humidity
Weather is important
atmospheric conditions at
a point in time
Salt Lake City Temperatures Dec 07
Observed, Normals, Records
Temp. at one
place over time
(temp-erature “time
series”)
Thickness, Composition & Thermal Structure of the Atmosphere
• Thickness = pressure and density of air decrease with elevation
• Chemical composition = elements (gasses) that make up air and remain nearly constant (so ignoring water, aerosols [very fine dust], pollution)
• Thermal Structure = How temperature changes with elevation in the atmosphere
Atmosphere Thickness and
Pressure
Pressure is caused by weight of air above, so pressure decreases with altitude
Pressure compresses air, so air becomes less dense or ‘thinner’ with altitude
Atmosphere has no distinct top; it just becomes less and less dense until for practical purposes there is no air, above ~ 100 km
Note: 1 km = 0.62 miles
Atmosphere Thickness and
Pressure
Where is the air?
• 50% below 6km altitude
• 90% below about 18km
• 0.00003% above 100km
Sealevel Pressure = 14.7 lb/in2 or 1013 mb or 29.9
inches (of mercury)Orem Pressure =12.5 lb/in2 or 855 mb
Composition of the Atmosphere Below ~ 80 km
altitude; Ionosphere exists higher
Nitrogen gas = N2
Oxygen gas = O2
= CO2
Gasses in Dry Air
• N2 (‘Nitrogen’) – 78%
• O2 (‘Oxygen’) – 21%
• Ar (Argon)– 1%
• CO2 (Carbon dioxide) – 0.37%
• Ne (Neon), He (Helium), CH4 (Methane), Kr
(Krypton), H2 (Hydrogen) – < 0.002%
Other, Variable Components of Air
• Water Vapor (H20) – 0 to 4%
• Aerosols (dust)
• Ozone (03)
All are important!
Examples include dust and air pollution
Aerosols are variable in concentration and location
Aerosols
Ionosphere
• Exists above ~ 80 km
• Radiation from Sun knocks electrons off gas molecules & atoms, ionizing them
• Ionosphere protects lower atmosphere from radiation by absorbing the energy (meaning we need it!)
Thermal Structure of the Atmosphere
Temperature changes with altitude create 4 distinct layers to the atmosphere:
Thermosphere – Above stratos.; T increase w/ height
Mesosphere – Above stratosphere to ~ 90 km; T decreases w/ height
Stratosphere – Above troposphere to ~ 50 km; T increases w/ height
Troposphere – Ground to 10 – 15 km altitude; T decreases w/ height. Weather happens in this layer!
• Weather affects many of our activities
• Weather events can be very expensive (droughts!)
• Weather can be deadly (droughts!)