ATMOSPHERE Part 2

Water Cycle

Air pressure- weight of the atmosphere

1. Caused by gravity

2. 14.7 lbs/ sq.in at sea level

Barometer- instrument to measure air pressure

Two types:

ANEROID

MERCURY

Clicker

• What causes air pressure?

a) Gravity

b) Inertia

c) Radiation

d) Friction SMART Response QuestionTo set the properties right click and selectSMART Response Question Object->Properties...

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:

HumidityThe 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

things that can change air pressure

Specific Humidity ACTUAL

amount of water vapor in the air at a given time and placeUnits - g of

water vapor / Kg of air

Saturated AirAt a steady temperature the

amount of water vapor is at it’s peak (maximum)

Rate of condensation = Rate of evaporation

• 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 pressureUNIT - %

Relative humidity = specific humidity X 100% maximum capacity(saturated)

100% Rel. Hum. – saturated air0% 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 QuestionTo set the properties right click and selectSMART Response Question Object->Properties...

Clicker Dry bulb=22 degrees:

Difference between bulb readings is 5 degrees what is the RH %?

SMART Response QuestionTo set the properties right click and selectSMART Response Question Object->Properties...

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

Temperature- warm 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) Lightb) Dustc) UV raysd) Mesosphere

SMART Response QuestionTo set the properties right click and selectSMART Response Question Object->Properties...

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 liftingb) Advective coolingc) Convective coolingd) Coalescence

SMART Response QuestionTo set the properties right click and selectSMART Response Question Object->Properties...

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” likeForm when warm moist air lie above a

layer of cool air

Cirrus

“feathery” highest cloudsForm 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

SupercoolingWater 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.