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 convectio n.  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.

ConvectionCurrents!

 Differences in air pressure  More of a difference in pressure = faster winds Lots of difference

 You know… › Warm air rises = less dense › Cool air sinks = more dense  Now understand… › Warm air = less dense = low pressure › Cool air = more dense = high pressure

 Created by unequal heating of Earth’s surface.

 The movement of air between the equator and the poles produces global winds.  Coriolis effect produces patterns of air circulation called global winds.

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

Doldrums Where the trade winds meet around the equatorWhere the trade winds meet around the equator Very little wind because the warm air rising = low pressureVery little wind because the warm air rising = low pressure

Horse Latitudes High pressure areas… 30 0 N and 30 0 SHigh pressure areas… 30 0 N and 30 0 S Very week windsVery week winds

 Bands of high speed winds  Upper troposphere and lower stratosphere  Blow from west to east at speeds of km/hr.  Help airplanes save fuel and time when traveling 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 distances.  They are caused by unequal heating of Earth’s surface within a small area.  Types: › sea breezes and land breezes › Mountain 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 direction and speed.  Wind direction is determined with a wind vane – points in the direction the wind is moving!  Wind speed is measured with an anemometer.  The increased cooling that a wind can cause is called the wind chill factor. Anemometer – The cups catch the wind, turning faster when the wind blows faster. Wind Vane