1. Layers of the Atmosphere 1

2.  The atmosphere is divided into layers according to major changes in its temperature.  Gravity holds the layers of the atmosphere on the surface of the Earth.  The amount of air pressure at a given altitude is dependent upon the weight of the atmosphere above that point.  The higher you go then, the lower the air pressure. 2

3.  Layer closest to Earth  Height varies  18-20 km at equator  6-8 km at the poles  Almost all weather occurs in this layer  Density decreases as height increases and temperature decreases as the air thins.  Radiant energy from sunlight heats the Earth’s surface. The ground then reradiates that heat to warm the air above it.  Temperature decreases as distance from the ground increases. 3

4.  Convection currents carry warm air upward  Watch the following videos about convection: http://www.youtube.com /watch?v=yZ3mYotx7ac http://www.youtube.com /watch?v=arp_4UJS2c  Temperature decreases about 6.5ºC for every kilometer increase in altitude  Average temperature at surface is 17ºC  Temperature at top of troposphere is about -51ºC. 4

5.  Transition layer between the troposphere and the layer above it  At about 12 km  The troposphere and the tropopause together make up the lower atmosphere. Anvil cloud: The “anvil” forms at the tropopause. photo by king nikochan on Flickr 5

6.  Above the tropopause up to about 50 km  In the lower stratosphere the temperature remains constant and very cold (~ -60˚C)  Generally eastward- blowing horizontal winds form the jet stream 6

7.  The ozone (O 3 ) layer is found in the stratosphere  Sometimes called the ozonosphere, it occurs from 16-50 km in altitude.  The ozone layer shields the Earth’s surface from harmful UV radiation  As ozone absorbs radiation it heats up, causing the increase in temperature of the stratosphere with increasing altitude.  Ozone is toxic to living things, so it is harmful when found near ground level. 7

8.  Transition layer between the stratosphere and the layer above it.  ~ 18˚C 8

9.  50-80 km above the Earth  Temperatures decrease as altitude increases, down to about -100˚C  Although the density of air is quite low, it is still enough to protect the Earth from most meteoroids (turning them into meteors) Peekskill Fireball, October 9, 1992  The transition between the mesosphere and the above layer is the mesopause. 9

10.  How hot or cold something is  A measure of how fast a substances molecules are moving  A measure of the average kinetic energy of a substance  Why do things feel hot or cold to us? 10

11.  Directly above the mesopause  Extends from about 90 km to between 500 and 1,000 km above the Earth  Temperatures climb sharply in the lower thermosphere then level off and hold fairly steady with increasing altitude  Temperatures in the upper thermosphere can range from about 500° C to 2,000°C or higher depending on solar activity.  Despite the high temperature it would feel very cold to us. Why?  The air density is so low that most of the thermosphere is what we normally think of as outer space  The space shuttle and the International Space Station both orbit Earth within the thermosphere 11

12.  The lower part of the thermosphere  Solar radiation (x-rays and UV rays) cause electrons to escape from atoms and molecules creating ions (electrically charged particles)  AM radio waves can be sent great distances by bouncing them off the ions in the ionosphere  At the top of the thermosphere  Altitude varies from 500-1,000 km as the thickness of the thermosphere varies 12

13.  The highest layer of the atmosphere  From the top of the thermopause up to 10,000 km  Sometimes considered to be the upper layer of the thermosphere  Air atoms and molecules are constantly escaping to space  Hydrogen and helium are the main components and are only present at extremely low densities.  Where many satellites orbit the Earth. 13