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Water in the Atmosphere
Hydrological(Water) Cycle
Hydrological Cycle vocabulary
Evaporation: the process of converting a liquid to a
gas
Transpiration: process where plants absorb water
through the roots and then give off water vapor
through pores in their leaves
Precipitation: any form of water that falls from a
cloud to Earth’s surface(rain, snow, sleet, hail,
glaze)
Evapotranspiration: the rapid cycling of water vapor
into the atmosphere by evaporation from Earth’s
surface or by transpiration from plant leaves
Hydrological Cycle vocabulary
Sublimation: conversion of a solid directly to a gas
without passing through the liquid state
Infiltration: movement of surface water into rock or
soil through cracks and pores
Percolation: the movement and filtering of fluids
through porous materials.
H2O exists in
atmosphere in all
three states of
matter…
Solid:
snow
hail
ice
Liquid:
rain and cloud
droplets
Gas:
invisible H2O
vapor
H2O may
change from
one state to
another:
Melting:
• from solid ice to liquid H2O
Freezing:
• liquid H2O to solid ice
Evaporation:
• from liquid H2O to H2O vapor
Condensation: from H2O vapor to
liquid H2O
Sublimation: change from solid
to H2O vapor
Example: Dry ice
Deposition: process of water vapor
turning directly into a solid
Frost on a window pane
Phase
Changes
: Turn
to page
505 and
copy
figure 2
into
your
notes.
Quick Check:
Use the chart you drew to assist you.
1. Is energy lost or
gained when a gas
changes into a solid?
2. What is the above
process called?
3. Name the process that
occurs when ice cream
absorbs 334 joules of
energy?
4. Give an example of
sublimation.
Atmospheric Moisture
• Invisible in the form of water vapor gas (only
what we can’t see)
• Where does it come from?
Insolation(energy from the sun) -- heats water
*changing it into a gaseous state
Warm air can hold much more water than cold air
Water vapor enters the
atmosphere from the
evaporation of water from
oceans, lakes, marshes and
glaciers
• Humidity:
water vapor in the air
• Described as
a. Specific humidity b.relative humidity
Relative Humidity
(The measure we encounter daily)
 Measure of the amount of water vapor present
in air relative to the maximum amount that the
air can contain at a given temperature (%)
– e.g. if relative humidity is 50%, then it contains 1/2 the
amount of water vapor it could hold at a given
temperature
 Relative humidity decreases as
temperature increases
Temp.
Increase,
ability to
hold
water
increases
Then
RH
Decreases
Relative Humidity and Temperature
Figure 4.7, p. 125
Relative humidity=specific humidity X 100
capacity (saturated)
Psychrometer: instruments used
to measure relative humidity
• Works on principle
that evaporation
causes cooling
• 2 thermometers…wetbulb and dry-bulb
• Readings show how
dry the air is
Dew point: the
temperature at which air
is saturated with water
vapor
• Dew, clouds, and fog forms
• If dew point is below
freezing, frost will form
Dew Point Temperature
• As air is cooled it eventually becomes
saturated (100% relative humidity)
• the temperature of saturation is called
the dew point temperature
• If cooling continues, condensation
begins and dew forms
Clouds: simply high
fogs, mist, or haze
• Form when air above surface
cools below dew point
• Shape depends on air
movement that forms it:
-horizontal air movement = layers
-vertical air movement = piles
• Temperature above freezing – clouds
drop water
• Temperature below freezing – clouds
drop snow crystals
Three main
cloud types:
CIRRUS:
- thin, feathery, made of ice
crystals
- form at high altitudes
- seen when weather is fair, but
can mean rain or snow
STRATUS
• Low sheets or layers; gray and smooth
• Block out the sun
• Associated with rain and drizzle
CUMULUS
• Piled in thick, puffy masses
• Formed by vertically rising air currents
• Usually mean fair weather
Other cloud
types:
Cirrostratus
Stratocumulus
Cirrocumulus
Altocumulus
Nimbostratus
Cumulonimbus:
large cloud that produce
LIGHTNING, THUNDER,
HEAVY SHOWERS =
Thunderstorms
Precipitation:
• Water that falls from the
atmosphere to the earth
• Occurs when cloud droplets grow
into drops heavy enough to fall to
Earth
FORMS OF PRECIPITATION
• Drizzle: fine drops, very close together,
fall slowly ….less than 0.5mm diameter
• Rain drops: larger, farther apart, fall
faster… 0.5mm to 5mm diameter
• Snow: falls in clumps of six-sided crystals
• Sleet: pellets of ice tha fall to the ground
when raindrops fall through freezing air
• Hail:
forms in cumulonimbus clouds-
irregular balls or lumps made of layers of ice
Acid precipitation: acid drops
that fall to the ground
- contain nitrate and sulfate
particles that come from burning
fuels, volcanoes and cars
Rain gauge:
instrument used
to measure the
amount of
rainfall
• Cloud seeding:
method to cause an increase
in precipitation
Condensation nuclei: suspended
particles that provide the
necessary surfaces for cloud
forming condensation.