Moisture, Clouds, & PrecipitationCh. 18

Earth-Space Science

Bremen High School

Teacher: Aaron McNeely

Water in the AtmosphereSec 18.1

Water vapor Water in a gas form The source of all clouds, condensation, and

precipitation For weather, water vapor is the most important

gas in the atmosphere Precipitation is any water, solid or liquid, that

falls from the sky Water vapor is 0-4% of atmospheric gases

Water’s Changes of State

Three states of matter: Solid, liquid, and gas

Water can change between these states in earth’s atmosphere, termed the water cycle

Water Cycle

Water constantly moves among the oceans, fresh water bodies, and atmosphere

Planet-wide phenomena powered by the sun

Steps in the Water Cycle General Steps:

Water evaporates from the ocean Water falls as precipitation upon land or ocean (cycle

complete) Water that falls on land becomes run-off or soaks into the

ground (infiltration) Run-off carries water directly back to the ocean in streams

and rivers Groundwater eventually joins lakes and rivers Plants absorb water and release it back into the

atmosphere (transpiration) Cycle complete when land-based water reaches the

ocean

Phenomena of the Water Cycle

Evaporation Precipitation Infiltration Run-off Transpiration

Water Cycle

http://www.metoffice.com/education/images/water_cycle.jpg

Water’s Changes of State

Evaporation—Liquid to gas Condensation—Gas to liquid Melting—Solid to liquid Freezing—Liquid to solid Sublimation—Solid to gas Deposition—Gas to solid

Evaporation

Liquid to a gas Energy required, termed latent heat Evaporation is a cooling process,

removes heat from surroundings

Condensation

Gas to liquid Latent heat is released Ex: Cold beverage, morning car

http://www.2xup-ph.org/album/discovery/condensation.jpg

Melting

Solid to liquid Heat required, used to break bonds

between water molecules Latent heat is the energy source for

weather such as thunderstorms, tornadoes, and hurricanes

http://www.phys.unsw.edu.au/~tonyt/dome%202003/melting%20ice.JPG

Freezing

Liquid to solid Water releases latent heat during

freezing Molecules in water become trapped in

the crystal structure of ice

                                                

http://www.bbc.co.uk/bristol/content/weather/2002/a2z/f/freezing_rain.shtml

Sublimation

Solid to gas, skips liquid phase Dry ice (frozen carbon dioxide)

sublimates, also freezer ice cubes can shrink

Dry ice

http://www.nwoutdoorgrrl.com/images/uploads/1953a.jpg

Deposition

Gas to a solid, opposite of sublimation Frost

http://fizyka.phys.put.poznan.pl/~pieransk/Physics%20Around%20Us/Frost%2001.jpg

Water’s Changes of State Diagram

•Red arrows = absorption of latent heat

•Blue arrows = release of latent heat

Humidity

Water vapor in the air Saturation occurs when air holds all

the water vapor that it is able to hold (at a particular temperature and pressure)

Saturated warm air holds more water than cool saturated air

Relative Humidity

A ratio of the air’s water vapor content compared to the amount it could possibly hold

Expressed as a percent 100% is saturated air

Changes in Relative Humidity

When the amount of water vapor in the air is constant: Lowering temperature increases

relative humidity Raising temperature decreases

relative humidity

Relative Humidity Example

Temperature = 20°C

Temperature = 10°C

Saturation = 14g water vapor

Saturation = 7g water vapor

Actual water vapor = 7g

Actual water vapor = 7g

Relative Humidity = 7g/14g = 50%

Relative humidity = 7g/7g = 100%

•Amount air can possibly hold

•Assume no water is taken or added from the parcel of air

•Relative humidity increases just by lowering temperature

Dew Point

A measure of humidity Dew point is the temperature at which a

quantity of air becomes saturated Below dew point, the air’s excess water

vapor condenses as dew, fog, or clouds High dew points indicate moist air, low dew

points indicate dry air (warm air holds more moisture, etc.)

http://static.flickr.com/38/89402458_8dd93eeb91_m.jpg

Dew on a Spider Web

Water Vapor for Saturation

Data: Table 1 on p. 506, Prentice Hall Earth Science

Water Vapor Needed for Saturation0.

1

0.3

0.75 2 3.

5 5 7

10

14

20

26.5

35

47

0

10

20

30

40

50

-40 -22 -4 14 32 41 50 59 68 77 86 95 104

Temperature (F)

Wat

er V

apo

r C

on

ten

t at

S

atu

rati

on

(g

/kg

)

Sling Psychrometer

Wet bulb

•Device to measure relative humidity, uses two thermometers and wet and dry bulbs

Adiabatic Temperature Changes (Sec 18.2)

Adiabatic heating or cooling Compressing or expanding air changes

temperature Compressed air is warmer ,expanded air

is cooler No heat is added or removed

Adiabatic Cooling

Rising air cools due to decrease in pressure

This adiabatic cooling causes clouds to form

Dry & Wet Adiabatic Rates

Rising air cools 10°C every 1000 meters, termed dry adiabatic cooling rate

After saturation, clouds form, cooling rate drops, termed wet adiabatic (5°C for every 1000 meters)

Wet & Dry Adiabatic Lapse Rates

http://geology.csupomona.edu/drjessey/class/Gsc101/adiabatic.gif

Cloud Formation by Adiabatic Cooling

Cooling = 10°C per 1000 m

Cooling = 5°C per 1000 m

Processes That Lift Air (for cloud creation)

Orographic lifting Frontal wedging Convergence Local convection

Orographic Lifting

When air is forced up the sides of mountains As the air rises, adiabatic cooling causes

cloud formation and precipitation Earth’s rainiest locations are often on the

windward sides of mountain ranges Leeward side of mountain range results in

rain shadow desert

Orographic Processes

Windward side

Leeward side

Orographic Clouds

http://home.online.no/~vteigen/orog2.jpg

Where is the air rising?

Take me to your leader.

http://www.lpl.arizona.edu/~jweirich/orographic_cloud.jpg

Frontal Wedging

Warm and cold air masses collide (fronts)

Warm air is forced up over the cooler air

Rising air cools adiabatically creating clouds, precipitation, and storms

Frontal Wedging and Clouds

Convergence

Occurs when air comes together after moving from different directions

Air rises at the collision and cools adiabatically creating clouds and storms

Convergence and Clouds

Convergence often creates storms in Florida

Local Convection

Differences in reflectivity, e.g., asphalt road versus grassy field create areas of warmer and cooler air

Rising warm air creates clouds Sinking cool air is clear Rising air also referred to as thermals Thermals affect birds and airplanes

Localized Convection

http://raanz.org.nz/wiki/uploads/TM/tmfig041.png

Birds and Thermals

Birds, like this condor, often sail using thermals

http://img1.travelblog.org/Photos/6108/22953/t/108896-Condor-sailing-on-thermals-0.jpg

Convective Cells

Convection cells often develop in stable air creating lumpy clouds (cumulus) separated by clear areas

Fair Weather Cumulus

Where is air rising and sinking?

http://webserv.chatsystems.com/~doswell/chasesums/05jun05_01.JPG

Stability

Temperature inversions, air overhead is warmer, creates stability

Warmer air acts as a cap over the cooler air

Surface air can become stagnant and polluted, dangerous air

Condensation Nuclei

Condensation nuclei are small particles around which water can start to condense

Needed for cloud formation Microscopic dust, smoke, ocean salt,

meteoritic material (space)

Tiny Particles

http://vortex.plymouth.edu/precip/dropsizes2.jpg

CloudsSec 18.3

Visible masses of tiny water droplets or ice crystals suspended in the atmosphere

Latin names Classified according to form (shape)

and height

Form and Height

Three Forms: Cirrus Cumulus Stratus

Heights: Low Middle (alto) High

Cirrus

Latin for “curl of hair” High, white, and thin, resemble

feathers or cotton candy Ice crystals

Cirrus Clouds

Cirrus clouds are high, white, and thin

Cumulus

Latin for “a pile” Rounded, lumpy cloud masses,

resemble cauliflower Normally a flat base and lumpy top Water droplets

Cumulus Clouds

http://www.lotc.com.au/images/scenes/sunset6.jpg

Cumulus clouds are

lumpy

Stratus

Latin for “a layer” Flat, layered, sheet-like clouds Extensive, create gray, dismal

conditions Low stratus clouds - water droplets High stratus clouds - ice crystals Often create halos around the sun or

moon

Stratus Clouds (flat)

Stratus clouds form

flat layers

High Clouds

Usually composed of ice crystals Examples:

Cirrus Cirrostratus Cirrocumulus

Cirrostratus

http://hea-www.harvard.edu/hrc.ARCHIVE/2004/2004243.000000-2004243.240000/SpaceWeather/swpod2004/28aug04/Koeman1.jpg

These clouds produced a halo around the sun

Middle Clouds

Middle clouds have the prefix alto in their names Examples:

Altostratus Altocumulus,

Altocumulus (middle-height, lumpy)

http://meteo.astronomie.cz/pic/ac06.jpg

Altostratus (middle, flat)

http://www.mmem.spschools.org/grade5science/weather/altostratus.jpeg

Low Clouds

Low clouds produce local weather such as rain

Prefix nimbo indicates rain Examples:

Stratus Stratocumulus Nimbostratus

Nimbostratus (rainy, low)

http://met.no/met/met_lex/q_u/skyer/nimbostratus/nimbostratus_bilder/nimbostratus1.jpg

Vertical Clouds

Vertical clouds extend through all of these height levels Example:

Cumulonimbus

Cumulonimbus (vertical)

Cumulonimbus clouds often create powerful storms

http://www.meteorologia.it/Fotoatlante/foto/

Cloud Classification

Cloud Summary Table

High Cirrus Cirrostratus Cirrocumulus

Middle Altostratus Altocumulus

Low Fog Stratus

Nimbostratus

Cumulus

Stratocumulus

C u

m u

l o

n I m

b u

s

Fog

When a cloud develops at ground level Results when the ground cools below

dew point Fog condenses in low areas Also can form by evaporation when

cool air moves over a warmer body of water

Fog in San Francisco

http://i1.trekearth.com/photos/19267/100_0032-5.jpg

Mechanisms of Precipitation

Tiny droplets of airborne moisture collect into larger masses

A one million times change in volume Two processes:

Bergeron process Collision-coalescence process

Bergeron Process

Cold clouds Supercooled droplets form ice crystals Fall as precipitation Supercooling occurs when droplets of

water remain in a liquid state even below the normal freezing temperature (0C)

Bergeron Process Diagram

•Ice crystal grow at the expense of cloud droplets

•Eventually the ice crystal becomes large enough to fall as precipitaiton (snow)

Collision-Coalescence Process

Warm clouds Condensation nuclei collect tiny

droplets of vapor Droplets succumb to gravity and fall as

precipitation

Forms of Precipitation

Function of temperature in lower atmosphere

Forms of Precipitation: Rain, Snow, Sleet, Glaze, Hail

Rain and Snow

Rain is drops of water at least 0.5mm in diameter

Snow (ice crystals) will survive on the ground if surface temp is below 39° F (4° C)

Snow can range from tiny crystals to large, fluffy clumps

Sleet & Glaze

Sleet: Small particles of clear ice, fleet forms when tiny water droplets descend through a colder air layer above the earth’s surface

Glaze: Fall of supercooled water droplets, can create clear ice coating on surface objects (ice storms)

Ice Storms

http://www.bellsystemmemorial.com/images/edward_kelly_photos/red_bank_nj_ice_storm_open_wire.jpg

Ice storms can result in power outages

Hail

Solid lumps of ice produced in cumulonimbus clouds

In these clouds, solid particles of ice move vertically and grow by collectiing supercooled droplets

Onion-like internal layers 5-140mm in size

Hailstones

http://www.crh.noaa.gov/arx/images/hail.061201.jpg

Hail Damage

http://externalweb.nmt.edu/reslife/hail/hail%202/Hail%20Storm%20damage%204.jpg

Acid Rain

Precipitation that forms in clouds containing air pollution

Pollution particles act as condensation nuclei

Acid rain can damage forests and stone structures

http://www.terradaily.com/images/forest-acid-rain-bg.jpg

Acid Rain and Stonework

1908 1968