STUVIA 2024/2025
GEOG 250 Midterm
Branch of geography that focuses on distribution and interactions of natural systems
and phenomena. - ✔✔Physical Geography
Decreases with altitude.
Most dense at sea level, gravity compresses.
-50% below 5.5 km
-90% below 16 km
-99% below 50 km - ✔✔Atmospheric Density
Pressure is due to the mass of the atmosphere above us pulled down and compressed
by gravity.
%
-Pressure decreases with height.
-Usually express altitude as pressure-heights. - ✔✔Atmospheric Pressure
Fixed gases:
-nitrogen: 78%
-oxygen: 21%
-argon: 1% (from radioactive isotopes in the crust)
-hydrogen, helium, neon, krypton, xenon
Variable gases:
-carbon dioxide: 0.0410% (levels rise in the winter due to plant decomp)
-water vapor: 0.01-4%
-ozone: 0.01%
-methane: 0.00019% - ✔✔Atmospheric Composition
How long an individual molecule will be used on average.
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, STUVIA 2024/2025
-nitrogen=12 million years
-oxygen=5k years
-CO2=5-10 years
-water vapor=10 days
-ozone=3 months
-methane=12 years - ✔✔Resident time
1. Homosphere (0-100 km): fixed gases evenly mixed throughout the layer. (contains
everything)
2. Heterosphere (above 100 km): gases layered by mass, with lighter gases
increasingly dominant as height increases. (basically nothing) - ✔✔Atmospheric
Structure (by composition)
-Troposphere: 10-16 km, heated by outgoing longwave radiation, 80-90% of mass,
tropopause.
-Stratosphere: 16-50 km, temp increases with height (inversion b/c moving into ozone
%
layer causes UV energy to be absorbed), stratopause.
-Mesosphere: 50-85 km, warmed from below by heat radiating up from stratosphere;
contains the lowest temps in the atm; mesopause.
-Thermosphere: approx. 85 km and up, temp. increases with height due to radiation
from the sun, density is very low, thermopause. - ✔✔Atmospheric Structure (by temp)
1. revolution (orbit) around the sun.
2. location on planet (latitude).
3. rotation around axis. - ✔✔What is surface radiation controlled by?
-Earth orbits in 'plane of the eliptic'
-Average distance is 93 million miles. - ✔✔Earth's Orbit
January 3rd
91.5 million miles
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, STUVIA 2024/2025
Closest point, +3% radiation input - ✔✔Perihelion
July 4th
94.5 million miles
Farthest point, -3% radiation input - ✔✔Aphelion
Incoming solar radiation in the upper atmosphere. - ✔✔Insolation
Earth is a sphere so parallel solar rays strike at different angles depending on the
latitude.
-Higher the latitude, the lower the sun angle.
-Lower sun angles result in longer path, lower intensity. - ✔✔Latitude (Sphericity)
Elevation angle of the sun above the horizon/
Higher sun angle=more intense radiation - ✔✔Sun Angle
23.5 degrees
%
Axis always points in same direction (axial parallelism) - ✔✔Tilt of Earth's Axis
Latitude where the sun is directly above. - ✔✔Declination
23.5 degrees north
The farthest point north where the sun is still directly overhead. - ✔✔Tropic of Cancer
23.5 degrees south
The furthest point south where the sun is still directly overhead. - ✔✔Tropic of
Capricorn
66.5 degrees north and south - ✔✔Arctic and Antarctic Circles
0 degrees latitude - ✔✔Equator
March 20th and Sept 20th
When the sun moves from one hemisphere to the next.
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