This document discusses water vapor and its role in atmospheric processes. It describes the three states of matter and how humidity is measured. It explains how clouds form at the dew point and how they are classified by height and type. The document also discusses different forms of precipitation and how they develop within clouds.

1. Water Vapor and
the Atmosphere

2. Water in the
Atmosphere
Precipitation is any
form of water that
falls from a cloud.
When it comes to
understanding
atmospheric processes,
water vapor is the
most important gas in
the atmosphere

3. Water Changes State
The three states of matter solid, liquid, and gas
(plasma is the fourth)

4. Humidity
amount of
water vapor in
air.

5. Relative
Humidity
Ratio of the air’s
actual water-vapor
content compared with
the amount of water
vapor air can hold at
that temperature and
pressure.
Lowering air
temperature causes an
increase in relative
humidity
Raising air
temperature causes a
decrease in relative
humidity

6. Dew Point
Dew point is the
temperature to
which a parcel of
air would need to
be cooled to
reach saturation.

7. How do I measure
humidity?
 Instrument: Hygrometer
 Psychrometer : a type of
hygrometer consisting of
two identical
thermometers mounted
side by side
 Dry bulb: give the present
air temperature
 Wet bulb: has thin wet
wick tied around the end

8. Cloud Formation
Clouds form
when air is
cooled to its
dew point

9. Clouds
Clouds are
classified on
the basis of
their form
and height.

10. Three Types of Clouds
Cirrus (cirrus = curl of hair)
high, white, and thin
Cumulus (cumulus = a pile)
rounded individual cloud
masses that have a flat base
and the appearance of rising
domes or towers
Stratus (stratus = a layer)
best described as sheets or
layers that cover much or all
of the sky

11. Classification of
Clouds by Height
High Clouds
 Have bases above 6000
meters
 Cirrus: high, white and thin
 Cirrostratus: flat layers
 Cirrocumulus: fluffy masses

12. Middle Clouds (Alto)
 Have bases between 2000 and
6000 meters
 Altocumulus: rounded masses
that are larger and denser
than cirrocumulus clouds
 Altostratus: uniform white to
grayish sheet covering the sky
with the sun or moon visible as
a bright spot

13. Low Clouds
 Have bases below 2000
meters
 Stratus: uniform layer of
clouds that covers much of the
sky
 Stratocumulus: scalloped
bottom that appears as long
parallel rolls or broken rounded
patches
 Nimbostratus: grayish clouds
covering most of the sky often
producing precipitation
 Cumulonimbus: cloud covering all

14. Fog
 A cloud with
its base at or
very near the
ground.

15. How Does Precipitation Form?
For precipitation
to form, cloud
droplets must
grow in volume
by roughly one
million times.

16. Forms of Precipitation
The type of precipitation
that reaches Earth’s
surface depends on the
temperature profile in the
lower few km of the
atmosphere
 Rain: drops of water that
fall from a cloud and have a
diameter of at least 0.5 mm
 Snow: light, fluffy, sixsided ice crystals

17. Forms of
Precipitation
Sleet: fall of small particles of
clear to translucent ice
Glaze: when raindrops become
supercooled as they fall through
subfreezing air and turns to ice
when they impact objects
 Hail: form of solid precipitation
which consists of balls of
irregular lumps of ice produced
in cumulonimbus clouds