| A | B |
|---|
| air pressure | the weight of the gases pressing down on the earth |
| atmosphere | the gas that surrounds the earth |
| barometer | an instrument that measures air pressure |
| cirrus clouds | high altitude clouds made of ice crystals |
| cumulus clouds | large clouds that have flat bases and rounded masses piled on top |
| dew point | the temperature at which water vapor turns to liquid water |
| humidity | the amount of moisture in the air |
| ionosphere | a layer in the upper atmosphere that begins in the mesosphere and extends upward through the thermosphere |
| mesosphere | the third layer in the atmosphere |
| ozone | a form of oxygen in a thin layer with the stratosphere |
| precipitation | any moisture that falls from the atmosphere |
| stratosphere | a layer in the atmosphere that begins about seven miles up; the second layer in the atmosphere |
| stratus clouds | low foglike clouds that lie in a flat layer over a wide area |
| thermosphere | the fifth layer in the atmosphere |
| troposphere | the first layer in the atmosphere ; the lower atmosphere in which most weather takes place |
