Download Chapter 19 The Atmosphere in Motion

Chapter 19 The Atmosphere in Motion
I Air pressure and the wind
A. What is air pressure?
1. A column of air that reaches from sea level to the
tom of the atmosphere pushes down at 147lbs per
square inch
2. Air pressure – is the weight of the overlying
atmosphere
3. It is exerted in all directions
4. Force pushing on your body is balanced by your
body pushing out
5. The higher you go into the atmosphere the lover the
pressure
6. Barometers – used to measure air pressure
a. Aneroid – evacuated can with read outs
attached and barograph
b. Mercury p 414
7. Units of air pressure
a. inches or millimeters – used to read mercury
b. millibars used on weather maps – these are
adjusted to sea level pressure due to altitude
differences
B. Why does air pressure Change
1. Elevation – higher up less air pressure
2. Temperature – the warmer(more spread out) the less
Air P.
3. Water Vapor – the more water vapor the lower
the A.P. – H2O molecules weigh less than the N &
O molecules in the air
4. Isobars – lines of equal pressure – closed isobar
forms a closed lop on a map
5. If pressure increases toward center it is a High
Pressure Center
6. Low pressure center – pressure is lower
7. Pressure Gradient – how close the isobars are. Close
together – large gradient
C. What makes the wind blow
1. Difference in A.P. – the greater the difference the
faster the winds. The closer the isobars the faster the
wind
2. A wind blows form High P. to low P.
e.g. Hot air on an island rises (form L.P.) Cool
air from the water (H.P) rushes in, this is
known as a sea breeze
D. Measuring surface wind direction and speed.
1. Wind vane – measure the direction from which the
wind is blowing – Winds are named by the
direction they come from
e.g. westerly or sea breeze
2. Anemometer – measure wind speed
II Factors affecting Wind
1. Coriolis Effect
1. If the earth did not spin and was perfectly smooth
air would flow strait from high pressure
areas(poles) directly to low pressure
areas(equator)
2. Coriolis effect causes objects traveling freely over
the earth to curve
a. In n. hemisphere curve right
b. In s. hemisphere curve left
c. The effect is greater near the poles
d. The effect is also greater in long diastase
travel vs. short travel
e. The effect increases with increased speed
3. Friction – with the earth’s surface slows winds
down. The smooth surface(water) the faster wind
can blow the higher coriolis effect
4. The coriolis effect is a strong factor in
determining wind direction as is a Pressure
gradient speed
5. Coriolis causes winds to blow counter clockwise in a
low, clockwise in high
6. Jet stream – swift winds due to low friction – direct
path of storms
III Global Wind Patterns
1. Non rotating earth would allow warm air to rise at the
equator, move to the poles and sink to travel back to
the equator, resulting in large circulation cell
2. The corriolis effect (Rotation of earth) prevents this
from happening
3. 3 cell circulation model
4. Weakness of 3Celled model
a. gives simplified view of circulation between 30 and
60
b. No effect given to continents or season
c. Simplifies upper level winds
B. Description of Wind and Pressure Belts
1. ITCZ (intertropical convergence zone) occurs at the
equator
a. hot and humid with little or no wind
b. rain is common
c. historically been called the doldrums
2. between 20 and 35 air sinks forming subtropical
highs, location of earth’s deserts. Known as horse
latitudes
3. between the doldrums and the horse latitudes are
the easterly trade winds
a. Warm and steady (speed and direction)
winds
IV Continental and Local Winds
A. effects of Seasons and continents
1. Seasons, land masses and topography causes winds
to vary from global patterns depicted in the 3cell
model
2. Hot air above land is summer creates low-pressure
cold air. Above oceans in summer creates high
pressure
e.g. Atantil Highs bring winds off the ocean into
the eastern sea board. Winter is reversed
3. Monsoons – winds caused by seasonal pressure
changes
B. Local winds – extent 100 km or less include sea breeze,
lond breeze, mountain breeze and valley breeze
1. Sea – land breeze - During day land is warmer
creating low pressure above` causes the cool
air(H) to blowing from the water (sea) and night
it reverse
2. Mnt. Breeze – at night the air against the
mountain cools more than the surround air and
sinks down hill
3. Valley breeze – mountain heats the air causing it
to rise and the air from the valley flows up hill