Download Chapter 19.2

Chapter 19.2
Pressure Centers and Winds
Highs and Lows
 Lows, or cyclones are centers of low
pressure. High, or anticyclones, are
centers of high pressure.
 In cyclones, the pressure decreases from
the outer isobar toward the center.
 In anticyclones, the pressure increases
from the outer isobar toward the center.
Cyclonic and Anticyclonic Winds
 When pressure gradient and the Coriolis
effect are applied to pressure centers in
Northern Hemisphere, winds blow
counterclockwise around a low. Around
a high they will blow clockwise.
 In either hemisphere friction causes a net
flow of air inward around a cyclone or
outward around an anticyclone.
Weather and Air Pressure
 A low pressure center will cause air to
accumulate and increase pressure so the
air will rise. The opposite is true in a high
center.
 Because of this low pressure centers will
produce clouds and precipitations and
give stormy weather.
Weathering Forecasting
 Low pressure centers can produce bad
weather. Lows will move from west to east
across the United States. They can have
an unpredictable path.
Global Winds
 The atmosphere can act as a giant heattransfer system. This system moves warm
air toward high latitudes and cool air
toward the equator.
Non-Rotating Earth Model
 In this model we have a theoretical nonrotating planet that has a completely
smooth surface of either all land or water.
There would be 2 large thermally
produced cells.
 The air at the equator will rise and move
toward the poles. This air would cool
down and move back toward the
equator.
Rotating Earth Model
 Because the Earth rotates these 2 cells break down into smaller cells.
 Near the equator, the rising air produces a pressure zone called an equatorial low
(produces a lot of precipitation). This warm air moves up 20 to 30 degrees, north or south
latitude then sinks toward the surface. This produces hot, arid condition called the
subtropics. We find deserts in this area. As air moves from this area it is deflected and
makes the trade winds. Trade winds are 2 belts of winds that blow almost constantly from
an easterly direction.
 The prevailing westerlies is the air that is deflected from the subtropics northward.
 Polar easterilies are winds that blow from the polar high toward the subpolar low. These
are not constant winds.
 The meeting of warm and cool air masses makes a polar front which is an area with many
storms.
Influence of Continents
 Large landmasses change how air flows and will produce changes in wind directions
called monsoons. This is were areas like India get a flow of warm, wet air from the Indian
Ocean so they have a very rainy season.