Chapter 18 Reading Guide
Water in the Atmosphere
18.1: Humidity and Condensation
1. List and describe the three states of water:
SOLID: ice, snow, and hail; temperatures of 0 C or below
LIQUID: rain, cloud droplets, temperatures between 0 C and 100 C
VAPOR: bubbles in boiling water; temperatures of 100 C or higher
2. Write two sentences comparing and contrasting specific and relative humidity; tell how
each is measured.
SPECIFIC HUMIDITY: measures the amount of water vapor actually present in water.
Measured in grams of water vapor/kg of air.
RELATIVE HUMIDITY: measures how close the air is to saturation. Stated as a
percentage (%).
3. The steps in cooling and condensation process:
1. Contact with Colder Surface: causes condensation on that surface
2. Radiation: ground loses heat and cools the air above, leaving droplets of water in the
air that take time to fall.
3. Mixing: warm air blows over cold ground, cooling the air and lowering and lowering it
below the dew point.
Condensation: change from vapor to liquid when air cools beyond its saturation point.
Condensation Nuclei: tiny particles around which condensation can accumulate.
1, 2, and 3 all lead to condensation (also nuclei).
18.2: Clouds
Complete the organizer with the information about the different types of clouds. Tell
whether each forms vertically or horizontally and at what altitude each is found. Describe
appearance and weather impact when possible.
Cirrostratus
Cirrocumulus
High altitude; horizontal; thin sheets that
High altitude; vertical; puffy clouds
may suggest precipitation
especially in the winter
Altostratus
Altocumulus
Middle altitude; horizontal; similar to
Middle altitude; vertical; similar to
cirrostratus
cirrocumulus
Nimbostratus
Stratocumulus
Low altitude; horizontal; dark gray layers
Low altitude; horizontal and vertical
of clouds that produce steady rain
Cumulonimbus/Cumulus
Can span many altitudes; vertical; cumulonimbus produce heavy rain with thunder and
lightning.
Tell how one cloud type from the above organizer forms:
Altostratus clouds form as air rises and cools in layers. These layers form when the
surrounding air is stable and forces rising air to move horizontally rather than vertically.
Cumulonimbus clouds begin forming when moist air rises and cools to its dew point.
Cumulus clouds form as air in a growing cumulus cloud moves upward because it is
buoyant and its temperature is warmer than that of the surrounding air.
Stratus clouds form in stable air. In stable air, air cannot easily move up or down, so it
tends to spread out horizontally in layers.
18.3: Precipitation
Complete the chart by describing the formation of each precipitation type. Include
information about temperature.
1. Rain
2. Sleet
3. Freezing Rain
4. Hail
5. Snow
Water droplets that have become big
enough to fall to the ground
Forms when rain falls into a layer of cold
air
Forms when raindrops freeze instantly
when they hit a solid surface
Forms when a frozen raindrop or clump of
ice crystals is blown back up repeatedly,
building up layers of ice before falling to
the ground
Forms when ice crystals in a cloud collide
and clump together
List and explain the factors that contribute to frequent precipitation in some areas and
dryness in other areas.
Precipitation forms in areas where air rises and produces condensation. These areas
include places near the equator where the sun’s heat raises land and air temperatures,
places with low pressure where storms are common, and places where moist air rises over
mountains and cools.
Dryness occurs in places where air sinks and warms. These places include areas of
persistent high pressure, areas with extremely cold temperatures, and areas on the
leeward side of mountains where dry air sinks.