What causes air pressure?

Air has mass. Air takes up space. Air has density. Air pressure is the

weight of a column of air pressing down on an area.

Atmosphere held in place by gravity Pressure strongest at surface-more air

above you *as altitude increases, air pressure

decreases› Stack of books

As Air Pressure decreases, so does density.

Atmosphere: a mixture of gases that surrounds Earth: acts like a blanket› Contains oxygen› Protects from sun

Troposphere: all weather happens here Stratosphere: ozone layer-protects us Mesosphere: middle layer Thermosphere: hottest layer

Nitrogen=78% Oxygen=21% Other 1%=water vapor, CO2 and other

Sun’s energy travels to earth as Electromagnetic waves.

What type of heat transfer is this?

Scattering: Reflections of light in all directions.

Why is the sky blue?

Ever feel the heat of the sun on your face or the heat from standing by a campfire? That is radiation.

It is the direct transfer of energy by electromagnetic waves through space.

Have you walked barefoot on the sand at the beach and the sand burned your feet? That is conduction.

It is the direct transfer of heat from one substance to another through direct contact.

Did you come in after the snow with wet shoes on and your mother told you to put them over the heating vent to dry? How does this dry them even though the actual furnace is in the attic? That is convection.

The transfer of heat by the movement of fluid or air. Hot air rises, cold air sinks.

Light/heat from the sun RADIATES through the atmosphere, hits the Earth where it is absorbed.

This heats the air above it by CONDUCTION.

This heat rises up to the greenhouse gases where it is trapped, cools, sinks and heats at the surface again.-CONVECTION.

These gases absorb the heat and act as a “blanket” to keep Earth warm.

Some greenhouse gases: water, methane, carbon dioxide.

Sun Gases Sun’s Rays

Air in the atmosphere acts as a fluid (water vapor). The sun's radiation strikes the ground = warming the rocks/ground. As the ground’s temperature rises due to conduction, heat energy is released into the atmosphere, forming a “bubble” of air which is warmer than the surrounding air. This “bubble” of air rises into the atmosphere. As it rises, the air in the “bubble” cools and becomes more dense. The movement of the air creates wind. Convection currents are responsible for many weather patterns in the troposphere.

ConvectioConvectionn

Currents!Currents!

Differences in air pressureDifferences in air pressure More of a difference in pressure = faster More of a difference in pressure = faster

windswinds

Lots of Lots of differencedifference

You know… › Warm air rises = less dense› Cool air sinks = more dense

Now understand…Now understand…› Warm air = less dense Warm air = less dense = low pressure= low pressure

› Cool air = more dense Cool air = more dense = high pressure= high pressure

Created by unequal heating of Earth’s Created by unequal heating of Earth’s surface.surface.

The movement of The movement of air between the air between the equator and the equator and the poles produces poles produces global winds.global winds.

Coriolis effectCoriolis effect produces patterns of produces patterns of air circulation called air circulation called global windsglobal winds..

Major global wind systems:Major global wind systems: Polar easterlies, westerlies, and trade winds.Polar easterlies, westerlies, and trade winds.

DoldrumsDoldrums• Where the trade winds meet around the Where the trade winds meet around the

equatorequator• Very little wind because the warm air Very little wind because the warm air

rising = low pressurerising = low pressure

Horse LatitudesHorse Latitudes• High pressure areas… 30High pressure areas… 3000N and 30N and 3000SS• Very week windsVery week winds

Bands of high speed Bands of high speed windswinds

Upper troposphere and Upper troposphere and lower stratospherelower stratosphere

Blow from west to east at Blow from west to east at speeds of 200-400 km/hr.speeds of 200-400 km/hr.

Help airplanes save fuel Help airplanes save fuel and time when traveling and time when traveling east.east.

Have you ever flown a kite at the beach on a hot summer day? Even if there is no wind inland, there may be a cool breeze blowing in from the water toward the beach. This breeze is an example of

local winds!

Local winds are winds that blow over short Local winds are winds that blow over short distances.distances.

They are caused by unequal heating of They are caused by unequal heating of Earth’s surface within a small area.Earth’s surface within a small area.

Types: Types: › sea breezes sea breezes and and land breezesland breezes› Mountain breeze and valley breezeMountain breeze and valley breeze

Land heats up faster than water. Hot air over land rises (Low Pressure), cool air over water falls (High Pressure). Winds move from the water (High Pressure) to the land (Low Pressure).

Land cools off faster than water. Cool air over land falls (High Pressure), warm air over water rises (Low Pressure). Winds move from the land (High Pressure) to the water (Low Pressure).

During the day the sun warms the air slopes, creating a valley breeze…

at nightfall, the air along the mountain slopes cools…

This cool air moves down the slopes into the valley, producing a mountain breeze!

Winds are described by their Winds are described by their direction and speed.direction and speed.

Wind direction is determined Wind direction is determined with a wind vane – points in the with a wind vane – points in the direction the wind is moving!direction the wind is moving!

Wind speed is measured with Wind speed is measured with an anemometer.an anemometer.

The increased cooling that a The increased cooling that a wind can cause is called the wind can cause is called the wind chill factor.wind chill factor.

Anemometer – The cups catch the wind, turning faster when the wind blows faster.

Wind Vane