Earth Science
19.2 Pressure Centers and Winds
I.High and Lows
Lows
Kyklon
Highs
Cyclones, centers of
low pressure
“moving in a circle”
Anticyclones, centers of
high pressure
***In cyclones, the
pressure decreases
from the outer isobars
toward the center. In
anitcyclones, just the
opposite is the case—
values of the isobars
increase from the
outside toward the
center.
Cyclonic and Anticyclonic Winds
***When the pressure
gradient and the and
the Coriolis effect are
applied pressure
centers in the Northern
Hemisphere, winds
blow counterclockwise
around a low. Around
a high, they blow
clockwise.
***In either
hemisphere, friction
causes a net flow of air
inward around a
cyclone and a net flow
of air outwards around
an anticyclone.
Weather and Air Pressure
Horizontal Convergence
Net inward movement
of air causes the area
occupied by the air
mass to shrink
Low Pressure Center
Causes a net
accumulation of air
which increases it
pressure
Weather Forecasting
Based on locations and
possible paths of
cyclones and
anticyclones
1) Cannot definitely
say this will happen
for sure
II. Global Winds
***The atmosphere
balances these
differences by acting as
a giant heat-transfer
system. This system
moves warm air toward
a high latitude and cool
air toward the equator.
Non Rotating Earth Model
Non-rotating planet
with a smooth surface
of either all land or all
water. Two large
thermally produced
cells would form
1) Heated air at the
equator would rise
until it reached the
tropopause
2) Tropopause would
deflect this air
toward the poles.
Rotating Earth Model
Effect of rotation were
added to the global
circulation model, the
two cell convection
system would break
down into smaller cells.
1) Polar Cells
2) Tropical /Sub
Tropical Cells
3) Middle latitudes
Ferrell Cells
Hadley Cells
Trade Winds
Two belts of winds that
blow almost constantly
from easterly
directions
1) Subtropical high
and equator
Westerlies
Remainder of the air
travels toward the
poles and is deflected
1) Middle latitudes
2) Dominant east to
west motion of
atmosphere
Polar Westerlies
Winds that blow from
the polar high toward
the subpolar low.
Polar Front
Cold polar air sinks and
spreads toward the
equator. Interaction of
these warm and cool
air masses produces a
stormy belt
Monsoons
Seasonal changes in
wind direction
Winter Monsoons Dominated by dry
continental air
Summer Monsoons
Warm months
experience a flow of
water-laden air from
Indian Ocean produced
rainy summer monsons