ATMOSPHERE Part 2

Water Cycle

Air pressure- weight of the atmosphere 1.Caused by gravity 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

Units of Measurement 1.Millibars- unit on national weather map 2.Inches of Mercury on local weather 1.Conversion ’’= 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:

Humidity The more water vapor in the air the lower the air pressure Dry air is more dense H 2 0 is molecularly lighter than N 2, O 2 and CO 2 things that can change air pressure

Specific Humidity  ACTUAL amount of water vapor in the air at a given time and place Units - g of water vapor / Kg of air SSaturated Air At 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 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, 1m 3 of air can hold 10 g of water vapor. What is the relative humidity at that temperature if 1 m 3 of air is holding 9 g of water?

Clicker  Dry bulb=22 degrees: Difference between bulb readings is 5 degrees what is the RH %?

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) Light b) Dust c) UV rays d) Mesosphere

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

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.