1. Water in the Atmosphere
Chapter 20 1 1

2. Forms of Water › Water exists in the atmosphere in 3 forms or phases:
Gas called water vapor
Solid known as ice
Liquid
› Water changes from one phase to the next when heat energy is absorbed or released

3. Some Vocabulary to Know
Latent heat – heat energy that is absorbed or released by a substance during a phase change
Evaporation – Most evaporation takes place in the oceans; water vapor can also enter the atmosphere by evaporation from lakes, streams, ponds, and soil.
Sublimation – process in which solid changes directly into a gas

4. Humidity Water vapor in the atmosphere is known as humidity
Controlled by rates of condensation & evaporation
Rate of evaporation is determined by temperature of air
Higher temperature, higher evaporation rate
Rate of condensation is determined by vapor pressure
Vapor pressure is part of the total atmospheric pressure caused by water vapor

5. Absolute humidity = mass of water vapor (grams)
Humidity Continued
Dew point – Temperature at which the condensation rate equals the evaporation rate. Temperatures below dew point, water droplets form
Absolute humidity – mass of water vapor contained in a given volume of air
Absolute humidity = mass of water vapor (grams)
Volume of air (cubic meters)
Relative humidity – ratio of the actual water vapor content of the air to the amount of water vapor needed to reach saturation.
Measure of how close the air is to reaching dew point.

6. Measuring Humidity
Relative humidity can be measured by: thin polymer film, a psychrometer, a dew cell, and a hair hygrometer.

7. Clouds & Fog
Clouds are a collection of small water droplets or ice crystals that fall slowly through the air.

8. Cloud Formation

9. Cooling Processes That Help Form Clouds
Four major processes that cause cooling for clouds to form:
1. Adiabatic Cooling – temperature of an air mass decreases as the air mass rises & expands
2. Mixing – when 1 body of moist air mixes with another body of moist air of a different temp
3. Lifting – forced upward movement of air results in cooling of air& cloud formation
4. Advective Cooling – temperature of an air mass decreases as the air mass moves over a cold surface

10. Classification of Clouds
CUMULUS CLOUDS
CHARACTERISTICS ---
Puffy
Vertical Growing Clouds
Thick
Looks like popcorn
Form thunderstorms
Cumulus – piled, heaped

11. STRATUS CLOUDS
CHARACTERISTICS --
Stratus - Sheet like
Low clouds
Layered
Covers large areas of the sky
Blocks the sun
“Covers” the earth

12. CIRRUS CLOUDS
CHARACTERISTICS --
Highest Clouds
Wispy
Feathery
Cirrus – curly
Made of ice crystals

13. Produce Hail, Lightning, and Thunder
CUMULONIMBUS CLOUDS
CHARACTERISTICS --
Thunderstorm Clouds
Produce Hail, Lightning, and Thunder
Anvil shaped
Can reach into the stratosphere
Nimbo - Rain

14. Fog Result of condensation of water vapor in the air.
Near the surface of Earth
2 types:
Radiation fog – results from the loss of heat by radiation; forms from the nightly cooling of Earth; layer of air in contact with the ground becomes chilled below dew point;
Advection fog – forms when warm, moist air moves across a cold surface; forms mostly along coasts.

15. Precipitation 4 forms of precipitation: Rain – liquid precipitation
Snow – common solid precipitation
Sleet – forms when rain falls through a layer of freezing air near the ground
Hail – solid precipitation in the form of lumps of ice

16. Causes of Precipitation
Coalescence – formation of a large droplet by the combination of smaller droplets
Supercooling – a condition in which a substance is cooled below its freezing point, condensation point, or sublimation point without going through a change in state

17. Measuring Precipitation
Meteorologists use a variety of instruments
Rain gauge
Doppler radar