Water vapor is the most important gas in the atmosphere. Clouds form when air is cooled to its dew point. There are three main types of clouds - cirrus, cumulus, and stratus - which are classified based on their height in the atmosphere. Precipitation forms as cloud droplets grow in size, with the type of precipitation depending on temperature profiles. Common forms of precipitation include rain, snow, sleet, glaze, and hail.

1. Water Vapor andWater Vapor and
the Atmospherethe Atmosphere

2. Water in theWater in the
AtmosphereAtmosphere
PrecipitationPrecipitation is anyis any
form of water thatform of water that
falls from a cloud.falls from a cloud.
When it comes toWhen it comes to
understandingunderstanding
atmospheric processes,atmospheric processes,
water vapor is thewater vapor is the
most important gas inmost important gas in
the atmospherethe atmosphere

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

4. HumidityHumidity
amount ofamount of
water vapor inwater vapor in
air.air.

5. RelativeRelative
HumidityHumidity
Ratio of the air’sRatio of the air’s
actual water-vaporactual water-vapor
content compared withcontent compared with
the amount of waterthe amount of water
vapor air can hold atvapor air can hold at
that temperature andthat temperature and
pressure.pressure.
Lowering airLowering air
temperature causes antemperature causes an
increase in relativeincrease in relative
humidityhumidity
Raising airRaising air
temperature causes atemperature causes a
decrease in relativedecrease in relative
humidityhumidity

6. Dew PointDew Point
Dew pointDew point is theis the
temperature totemperature to
which a parcel ofwhich a parcel of
air would need toair would need to
be cooled tobe cooled to
reach saturation.reach saturation.

7. How do I measureHow do I measure
humidity?humidity?
 Instrument:Instrument: HygrometerHygrometer
 Psychrometer : a type ofPsychrometer : a type of
hygrometer consisting ofhygrometer consisting of
two identicaltwo identical
thermometers mountedthermometers mounted
side by sideside by side
 Dry bulb: give the presentDry bulb: give the present
air temperatureair temperature
 Wet bulb: has thin wetWet bulb: has thin wet
wick tied around the endwick tied around the end

8. Cloud FormationCloud Formation
Clouds formClouds form
when air iswhen air is
cooled to itscooled to its
dew pointdew point

9. CloudsClouds
Clouds areClouds are
classified onclassified on
the basis ofthe basis of
their formtheir form
and height.and height.

10. Three Types of CloudsThree Types of Clouds
CirrusCirrus ((cirruscirrus = curl of hair)= curl of hair)
high, white, and thinhigh, white, and thin
CumulusCumulus ((cumuluscumulus = a pile)= a pile)
rounded individual cloudrounded individual cloud
masses that have a flat basemasses that have a flat base
and the appearance of risingand the appearance of rising
domes or towersdomes or towers
StratusStratus ((stratusstratus = a layer)= a layer)
best described as sheets orbest described as sheets or
layers that cover much or alllayers that cover much or all
of the skyof the sky

11. Classification ofClassification of
Clouds by HeightClouds by Height
High CloudsHigh Clouds
 Have bases above 6000Have bases above 6000
metersmeters
 Cirrus: high, white and thinCirrus: high, white and thin
 Cirrostratus: flat layersCirrostratus: flat layers
 Cirrocumulus: fluffy massesCirrocumulus: fluffy masses

12. Middle Clouds (Alto)Middle Clouds (Alto)
 Have bases between 2000 andHave bases between 2000 and
6000 meters6000 meters
 Altocumulus: rounded massesAltocumulus: rounded masses
that are larger and denserthat are larger and denser
than cirrocumulus cloudsthan cirrocumulus clouds
 Altostratus: uniform white toAltostratus: uniform white to
grayish sheet covering the skygrayish sheet covering the sky
with the sun or moon visible aswith the sun or moon visible as
a bright spota bright spot

13. Low CloudsLow Clouds
 Have bases below 2000Have bases below 2000
metersmeters
 Stratus: uniform layer ofStratus: uniform layer of
clouds that covers much of theclouds that covers much of the
skysky
 Stratocumulus: scallopedStratocumulus: scalloped
bottom that appears as longbottom that appears as long
parallel rolls or broken roundedparallel rolls or broken rounded
patchespatches
 Nimbostratus: grayish cloudsNimbostratus: grayish clouds
covering most of the sky oftencovering most of the sky often
producing precipitationproducing precipitation
 Cumulonimbus: cloud covering allCumulonimbus: cloud covering all

14. FogFog
 A cloud withA cloud with
its base at orits base at or
very near thevery near the
ground.ground.

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

16. Forms of PrecipitationForms of Precipitation
The type of precipitationThe type of precipitation
that reaches Earth’sthat reaches Earth’s
surface depends on thesurface depends on the
temperature profile in thetemperature profile in the
lower few km of thelower few km of the
atmosphereatmosphere
 RainRain:: drops of water thatdrops of water that
fall from a cloud and have afall from a cloud and have a
diameter of at least 0.5 mmdiameter of at least 0.5 mm
 SnowSnow:: light, fluffy,light, fluffy, six-six-
sided ice crystalssided ice crystals

17. Forms ofForms of
PrecipitationPrecipitation
SleetSleet: fall of small particles of: fall of small particles of
clear to translucent iceclear to translucent ice
GlazeGlaze: when raindrops become: when raindrops become
supercooled as they fall throughsupercooled as they fall through
subfreezing air and turns to icesubfreezing air and turns to ice
when they impact objectswhen they impact objects
 HailHail: form of solid precipitation: form of solid precipitation
which consists of balls ofwhich consists of balls of
irregular lumps of ice producedirregular lumps of ice produced
in cumulonimbus cloudsin cumulonimbus clouds