Transcript Review 4 Currents and Atmosphere

TCAP Review 4
What are Ocean Currents?
 Currents are streamlike movements of water found at
the surface or deep in an ocean.
 There are two types: Surface and Deep
Surface Currents
 Horizontal movement caused by winds near the
oceans surface
 Two examples: Gulf Stream and California
Current
 Three Factors: global winds, Coriolis effect,
continental deflections
Global Winds
 Winds cause the currents to flow in different
directions
 Equator= east to west
 Poles = west to east
Coriolis Effect
 Curving of moving objects
from a straight path due to
Earth’s rotation
 Northern hemisphereclockwise
 Southern hemispherecounterclockwise
Continental Deflections
 Currents change directions
by hitting the continents or
landmasses
Deep Currents
 A stream like movement of ocean water far below
the surface
 Form where water density increases
 Decreasing water temperature and increasing
water salinity increase density.
 Examples: North Atlantic Deep Water and Antarctic
Bottom Water
Deep Currents can form by
 Decreasing temperature
 When water gets cold its becomes more dense and sinks
then flows.
 Increasing salinity through freezing
 When ocean water freezes the salt is squeezed out
increasing the salinity of the remaining water making it
more dense, so it sinks then flows.
 Increasing salinity through evaporation
 When ocean water evaporates the salt is left behind
increasing the salinity of the remaining water making it
more dense, so it sinks then flows.
Currents and Climates
 Surface currents gently cool or warm the coastal
areas year round
 Some surface currents change their circulation pattern
causing changes in the atmosphere that affect the
climate in many parts of the world.
Warm Water Currents and
Climates
Warm water currents create warmer
climates in coastal areas.
Warm water surface currents travel from the
equator towards the poles.
Cold Water Currents and
Climates
Cold water current bring cooler
climates into areas.
Cold water surface currents travel from the poles
towards the equator.
Our Atmosphere
 The atmosphere is a mixture of gases that surrounds
Earth. In addition to containing the oxygen you need
to breathe, the atmosphere protects you from the sun’s
damaging rays. The atmosphere is always changing.
Every breath you take, every tree that is planted, and
every vehicle you ride in affects the atmosphere’s
composition.
Our atmosphere
Nitrogen, the most common
atmospheric gas, is released
when dead plants and dead
animals break down and when
volcanoes erupt.
Oxygen, the second most common
atmospheric gas, is made
by phytoplankton and plants.
The remaining 1% of the
atmosphere is made up of argon,
carbon dioxide, water vapor, and
other gases.
Air pressure
 The atmosphere is held around the Earth by gravity.
Gravity pulls gas molecules in the atmosphere toward
the Earth’s surface, causing air pressure. Air pressure is
the measure of the force with which air molecules
push on a surface. Air pressure is strongest at the
Earth’s surface because more air is above you. As
you move farther away from the Earth’s surface, fewer
gas molecules are above you. So, as altitude increases,
air pressure decreases.
Atmospheric Heating
 Thermal energy is transferred in one of three way:
 Radiation
 Convection (circulating currents)
 Thermal conduction
Radiation
 The Earth receives energy from the sun by radiation. Radiation
is
the transfer of energy as electromagnetic waves.
Although the sun radiates a huge amount of energy, Earth receives only
about two-billionths of this energy. But this small fraction of energy is
enough to drive the weather cycle and make Earth habitable.
Convection
 Convection is the transfer of thermal energy by the
circulation or movement of a liquid or gas.
 Most thermal energy in the atmosphere is transferred by convection.
For example, as air is heated, it becomes less dense and rises. Cool air is
denser, so it sinks. As the cool air sinks, it pushes the warm air up. The
cool air is eventually heated by the Earth’s surface and begins to rise
again. This cycle of
warm air rising and cool air
sinking causes a circular movement of air, called a
convection current.
Convection
Thermal conduction
 If you have ever touched something hot, you have
experienced the process of conduction. Thermal
conduction is the transfer of thermal energy
through a material. Thermal energy is always
transferred from warm to cold areas. When air
molecules come into direct contact with the warm
surface of Earth, thermal energy is transferred to the
atmosphere
Thermal Conduction
Wind
 The movement of air caused by differences in air
pressure is called wind. The greater the pressure
difference, the faster the wind moves. Differences
in air pressure are generally caused by the unequal
heating of the Earth by the Sun ( solar energy). The
equator receives more direct solar energy than other
latitudes, so air at the equator is warmer and less dense
than the surrounding air. Warm, less dense air rises and
creates an area of low pressure. This warm, rising air flows
toward the poles. At the poles, the air is colder and denser
than the surrounding air, so it sinks. As the cold air sinks, it
creates areas of high pressure around the poles. This cold
polar air then flows toward the equator.
Wind
Pressure Belts
Local Winds
 Local winds generally move short distances and can
blow from any direction. Local geographic features,
such as a shoreline or a mountain, can produce
temperature differences that cause local winds. During
the day, the land heats up faster than the water, so the
air above the land becomes warmer than the air above
the ocean. The warm land air rises, and the cold ocean
air flows in to replace it. At night, the land cools faster
than water, so the wind blows toward the ocean.
Land Breeze
 A land breeze is a type of wind that blows from the
land to the ocean. When there is a temperature difference between the land
surface and the ocean, winds will move offshore. Although commonly associated
with ocean shorelines, land breezes can also be experienced near any large
body of water such as a lake. Land breezes usually occur at
night. During the day, the sun will heat land surfaces, but only to a depth of
a few inches. At night, water will retain more of its heat than land surfaces.
Water has a high heat capacity which is one reason hurricane season officially
extends through the chilly November months.
 At night, the temperature of the land cools quickly without the insolation from
the sun. Heat is rapidly re-radiated back to the surrounding air. The water
along the shore will then be warmer than the coastal land creating a net
movement of air from the land surfaces towards the ocean.
Land Breeze
Sea Breeze
 A sea breeze happens during the day when cool air from
the water travels to replace the warm over the land. Land
heats up faster than the water. The air over the land begins
to warm and since warm air is less dense than cool air, it
rises as it is lighter than the cooler air above it. As the warm
air rises over the land, the cooler air over the water begins
to move in to replace the air that is rising over the land.
This causes the wind at the surface to switch direction and
blow from the water. As the afternoon wears on, the sea
breeze normally strengthens and moves further and further
inland. Its cooling relief can sometimes be felt many miles
inland. Once the sun sets, the air over the land begins to
cool and the air stops rising.
Sea Breeze
Mountain an Valley Breezes
 In areas where there are mountains and valleys we see a
type of wind pattern known as mountain breezes and
valley breezes. During the day, the surface of the mountain
heats the air high up in the atmosphere, quicker than the
valley floor can. As the warmer air expands a low pressure
is created near the top of the mountain. This attracts the air
from the valley, creating a breeze that blows from the valley
floor up towards the top of the mountain. Often birds
known as raptors, such as eagles, hawks, condors and
vultures, float on these breezes to preserve their energy.
This wind pattern is known as a valley breeze.
Mountain and Valley Breezes