A. Weather and Climate
(1) Pressure: Force (F) per unit Area (A); (F/A) exerted by air molecules
We have 3 temperature scales:
a) Degrees Fahrenheit:
32 0F = freezing point of water
212 0F = boiling pt. of water
b) Degrees Celsius (0C):
Zero 0C = freezing point of water
100 0C = boiling point of water
c) Kelvin Scale (Absolute Scale)
Zero K = coldest possible temp = no moleculecular
motion
273 K = freezing pt. of water = 0 0C
=32 0F
373 K = boiling pt of water = 100 0Celsius = 212 0F
** 1 degree of Celsius = 1 degree Kelvin * * (i.o.w., the size of a
degree Celsius is equal to that of the size of one degree Kelvin)
0C = K - 273, K = 0C + 273
0C = 5/9(F - 32); F = 9/5C + 32
C. Evolution of Earth's Atmosphere
Earth's atmosphere has changed significantly since the Earth was first formed!
1) Primordial Atmosphere - derived from the solar nebula (existed short time frame)
2) Evolutionary Atmosphere - gases derrived from the earth's
interior - outgassing; "purple sulfur bacteria" produced organic
materials from inorganic
elements (3.6 billion yrs ago)
3) Living Atmosphere - first photosynthesis by "blue-green algae" (3.3 billion yrs ago)
4) Modern Atmosphere - abundance of life as a consequence of
high levels of oxygen
D. Earth's Present Day Atmosphere
Defn - Atmosphere - a thin envelope of gases that
surrounds the earth. It is held to the earth by the force of gravity, and
it moves with the earth as the earth rotates.
(1) Composition of the Atmosphere
Natural Air = clean air + pollutants
Clean Air = dry air + water vapor
Dry Air (in % by volume):
Nitrogen (N2) 78.08%
Oxygen (O2) 20.95%
Argon (Ar) 0.93%
Trace Gases: He, Ne, Kr, Xe, Rn, H2
Water Vapor - a variable constituent of clean air
Variable constituents of dry air (trace amounts):
Ozone (O3), carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx, ), carbon dioxide (CO2)
(2). Vertical Structure of the Atmosphere
Pressure (weight of the overlying atmosphere):
Density - [mass per unit volume (m/v)] of the atmosphere also
decreases with height above the ground.
Height Above the Ground Fraction of the Atmosphere Below
5.5 km (3.4 mi) 1/2
11 km (6.8 mi) 3/4
16.5 km (10.2 mi) 9/10
32 km (19.9 mi)
99/100
Temperature - the atmos. can be classified by layers based on
the average vertical temperature profile.
Average Variation of Temperature with Altitude within
the Atmosphere
Troposphere:
The layer of the atmosphere nearest the earth to ~ 10 km) where temperature generally decreases with height.
The layer above the troposphere (~ 10-50 km) where temperature generally increases w/height
Vertical Structure By Composition:
"homosphere" (0-80 km)- a well mixed region where the composition is uniform (78% N2, 21% O2, etc.) due to turbulent mixing
"heterosphere"(80 km - gases are layered by atomic weight - less mixing here
Vertical Structure By Function:
"ionosphere" (mainly in the thermosphere) - an electrified
region within the upper atmosphere where large concentrations of ions and
free electrons exist - it filters harmful wavelengths of solar radiaton