Understanding the Weather Atmosphere Basics
Atmosphere provides oxygen, life, water
vapor (creates weather), convection
(storms)
Layers
troposphere - 99% of weather, lowest
layer, 5-10 miles up, temp. decreases as
altitude increases.
stratosphere - 10-30 miles up, temp.
increases as altitude inc., ozone layer
mesosphere - middle, coldest layer (130°F)
thermosphere - warm layer, ionosphere
(2700°F)
-x rays, UV rays broken apart here and
reflects radio transmissions back to
Earth,
-protects from meteors, creates auroras,
satellites orbit here.
exosphere - 570 - 3000°F
-space shuttle, satellites, auroras, gases
He, N, O , Ar
Sources of weather
Sun’s heat is the origin of all weather
air pressure - air molecules constantly
pushing down on us
-increase collisions - increase pressure,
-14.7 lbs / in2, 980 - 1040 mb @ sea
level
convection - warmed material is less dense
so rises, cools and sinks
warm vs. cold - fast moving, expands,
less dense vs. slow, shrink, more dense
air rising / air sinking - rising is low
pressure, sinking is high pressure
high to low pressure - wind blows from H
to L pressure,
- Increase in difference of pressures,
increase in wind speed
-higher wind speed has closer isobars,
low wind speed has widely
spaced
isobars
clear vs. clouds - air sinks vs. air rises,
cools, condenses forms clouds
Seasons & cycles
amount of energy reaching earth’s surface
varies and influences climate
earth’s orbit - ellipitical orbit which brings
Earth closer to sun @ certain times
increasing the amount of radiation
rotation - spinning on its axis creating high
and low temperatures
seasons - tilt is 23.5° to or away from sun,
so receives direct or indirect rays, S.
Hemisphere has reversed seasons due to
tilt.
Global Winds
heat @ equator, rises,low pressure, clouds,
rain, when reaches tropopause spreads to
poles, cools, sinks @ 30°N & S, high
pressure, clear.
Wind Cells
Hadley Cells - air rises at equator (0°) and
sinks at 30°N & S, George Hadley
polar fronts - air moves poleward at 60°N &
S meets cold polar air
Ferrel Cells - circulation between 30° &
60°N & S
rest of air sinks at poles
Coriolus Effect most pronounced at poles
(Gustave-Gaspard de Coriolus)
clockwise - deflected to right in N.
Hemisphere, high pressure spirals
counterclockwise - deflected to left in N.
Hemisphere, low pressure spirals
Jet streams are high speed winds that
develop from temperature and pressure
differences
-30,000 - 35,000 ft; speed 180 mph
-strengthen and steers low pressure
systems
-winter - greater contrasts, shifted toward
equator
-summer - equalized, weakens and goes
to poles
Famous winds
chinook - warm downsloped winds of the
Rockies
foehn - warm downsloped winds of
Switzerland
mistral - cold dry spiral conditions in France,
wind forced through a valley
Frontal systems are created as air masses
move around
Warm fronts - warm air moves over cold
-characteristics - cirrus, middle level
clouds, stratus with widespread precip,
strong winds up to a day
Cold fronts - cold air forces warm air up
-characteristics - cumulus &
cumulonimbus clouds with storms & heavy
rain
Stationary fronts - stalls out for a day or two
Occluded fronts - cold air colliding with
another cold front
Air Pressure movement in N. Hemisphere
caused by coriolus effect
-low pressure cycles counterclockwise away
from the Earth’s surface
-high pressure cycles clockwise down to the
Earth’s surface
Mountain weather
-windward side - clouds & rain
-leeward side - dry & desert