Transcript Atmospheric Pressure - Grosse Pointe Public School System

ATMOSPHERE Part 2
Water Cycle
Air pressureweight of the atmosphere
1. Caused by gravity
2. 14.7 lbs/ sq.in at sea level
Barometer- instrument to
measure air pressure
MERCURY
Two types:
ANEROID
Clicker
• What causes air pressure?
a)
b)
c)
d)
Gravity
Inertia
Radiation
Friction
SMART Response Ques
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Units of Measurement
1.Millibars- unit on national weather map
2.Inches of Mercury on local weather
1.Conversion- 29.92’’= 1013.25 mb
Latent heat
• Energy absorbed and stored in molecules
“hidden”
Homework
• Define/ research:
– Psychrometer
Psychrometer

Instrument to
measure humidity

Dry bulb –
measures air temp.
Wet bulb – has a
water soak wick
around the bulb –
water evaporates –
cools the air

Psychrometer
Dry air - greater evaporation
- greater cooling
- greater the difference in the 2
temperatures
High humidity – no evaporation (saturated air)
- temperatures of the 2 bulbs
will be the same or very close
Chart:
things that can change air
pressure
Humidity
The more water vapor in the air the
lower the air pressure
Dry air is more dense
H20 is molecularly lighter than N2, O2
and CO2
Specific Humidity

ACTUAL
 Saturated Air
amount of
 At a steady temperature the
water vapor in
amount of water vapor is at it’s
the air at a
peak (maximum)
given time and
Rate of condensation = Rate of evaporation
place
 Units - g of
water vapor /
Kg of air
• Dependent on air temperature
• Higher the air temp. - greater
the amount of water vapor in
the air
Relative Humidity

Comparison of the specific humidity and the
maximum amount of water vapor that the air
can hold at a given temperature and pressure
 UNIT - %
Relative humidity = specific humidity X 100%
maximum capacity(saturated)
100% Rel. Hum. – saturated air
0% Rel. Hum. – dry air
Clicker

At any given temperature , 1m3 of air
can hold 10 g of water vapor. What is
the relative humidity at that
temperature if 1 m3 of air is holding 9
g of water?
SMART Response Question
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
Clicker
Dry bulb=22
degrees: Difference
between bulb
readings is 5
degrees what is the
RH %?
SMART Response Questi
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things that can change air pressure
Altitude ( elevation )As altitude increases; air pressure
decreases
Fewer gas molecules= less pressure
Greatest at sea level or below
Least at the top of mountains
things that can change air pressure
Temperaturewarm air becomes less dense than cold air
– Becomes a low pressure
• As temperature increases air
pressure decreases
• Cold air will be a high pressure
Dew point: The temperature air
must be cooled to in order to reach
Saturation.

Any point below water vapor will
condense into liquid water.

If dew point falls below freezing point
of water we get FROST.
Cloud Formation

Clouds are made of which two states of
matter?
 Water Vapor (gas)
 Liquid water
Clicker

Water needs to condense on a solid
surface there are no solid surfaces in
the atmosphere. Using what you know
about scattering, what is needed to
allow water vapor to condense into a
cloud?
a) Light
b) Dust
c) UV rays
d) Mesosphere
SMART Response Ques
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Condensation nuclei

Dust, ice, salt, and other solid
particles suspended in the
atmosphere.
What else is necessary to form a cloud?
*Hypothesis*
Cloud formation: 2 methods

Method 1:
 Convective cooling
○ The lowering of the temperature of a mass
of air due to rising and expanding.
○ Most clouds form this way

Temperature changes that occur this
way are called Adiabatic temperature
changes.
Describe and Diagram
Method 2: Force lifting
Cloud formation requires rising air
 lifting can come from air forced up
terrain, air being heated and becoming
buoyant, frontal systems passing
through, etc.

Clicker

How are most clouds formed?
a) Force lifting
b) Advective cooling
c) Convective cooling
d) Coalescence
SMART Response Quest
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Describe and Diagram: Frontal lifting
Describe and Diagram: Orographic
Lifting
(Barrier)
Cloud Identification: the basics
Cumulus

“Puffy” thick high topped clouds
 Formed by rising moist air that cools
Stratus

“sheet” like
 Form when warm moist air lie above a
layer of cool air
Cirrus

“feathery” highest clouds
 Form above 6000 m (19685 ft)
Prefix/ Suffix

Alto: Middle

Cirro: Curly

Nimbo/nimbus: Rain
Precipitation
Rain: liquid water in the form of
droplets
Freezing Rain: rain that falls
when surface temperatures are
below freezing.
Snow: precipitation in the form of
flakes of crystalline water ice that
falls from clouds.
Sleet: form of precipitation
consisting of small, translucent
balls of ice. Ice pellets are usually
smaller than hailstones
Hail: solid precipitation. It consists
of balls or irregular lumps of ice,
each of which is called a hailstone.
Rain making processes

Coalescence
 Different size water
droplets
 Combine to form
larger

Supercooling
 Water droplets
commonly remain as
liquid water and do
not freeze, even well
below 0 degrees.
 Freezing
condensation nuclei
Cloud seeding: form of intentional
weather modification

dispersing substances into the air that
serve as cloud condensation or ice
nuclei.