11.3 Moisture in the atmosphere

Pages 285 - 291

Goal 1

Explain how clouds are formed

• Three basic steps– 1. Air mass rises– 2. Air mass cools and expands– 3. LCL reached for condensation to form

clouds

• Step 1– Air mass rises by the following mechanisms

• Convection current• Orographic lifting• Different temperature air mass collision

• Air mass rising by convection– Air mass warms up– Air mass flows up in atmosphere– Clouds form when LCL reached

• Air mass rising by orographic lifting– Air mass forced up mountainside– Cloud forms when LCL reached

Air mass rising by collision

• Air mass rising by collision– Cold air mass collides with warm air mass– Warm air mass forced up– Cloud forms when LCL reached

• Step 2– Air mass expands and cools– Lower pressure at higher altitudes allow air

mass to expand / spread out

• Step 3– LCL reached (dew point temp of cloud)– Condensation occurs around condensation

nuclei– Voila! A cloud!

• Stability– Air mass resistance to rising

• Cold surface• Warm neighboring air masses

• Latent heat– Energy released from condensation– Provides energy to storm system

• Warms air mass more• More rising• More condensation• More warming• Etc….

Goal 2

Identify various types of clouds and give their characteristics

• Classification system– Height

• Cirro (way high!! > 6 km)

• Alto (kinda high 2 – 6 km)

• Strato (low < 2 km)

• Classification system

– Shape

• Cirrus = wispy

• Cumulus = puffy

• Stratus = sheets

• Nimbus = low, gray, rain clouds

• Low clouds (liquid or ice)– Nimbostratus

• Low, gray rain clouds

• Low clouds– Stratocumulus

• Low, puffy white clouds

• Low clouds– Stratus

• Featureless

• Middle clouds (liquid or ice)– Altocumulus

• “sputtery”

• Middle clouds– Altostratus

• Featureless, more so than low lying stratus

• High clouds – Cirrocumulus (super cooled water)

• Translucent, fish scales

PD - gov

• High clouds – Cirrus (ice)

• Wispy

• High clouds – Cirrostratus

• Translucent, sheets

• Vertical development – Cumulonimbus

• Towering clouds• Up to the stratosphere• Storms

Goal 3

Describe the water cycle

• Amount of water on Earth is constant– 97% in oceans– 2% Freshwater frozen in polar icecaps– 1% cycling through water cycle

• Atmosphere• Surface• Sun’s energy

Water Cycle

• Step 1: Evaporation– Sun radiation EVAPORATES water

• Lakes• Streams• Oceans

Water Cycle

• Step 2: Condensation– Water vapor cools and CONDENSES– Condensation nuclei– Clouds are formed

Water Cycle

• Step 3: Precipitation– Water droplets coalesce (grow)– Precipitation occurs (water falls to ground)

• Bodies of water• Run-off

• Cycle starts over…

PD - gov

Goal 4

Describe types of precipitation

• Rain– Liquid entire time– Forms as liquid– Falls as liquid

• Snow– Frozen entire time– Forms as ice crystals– Falls as ice crystals

• Sleet– Melts and refreezes when falling to Earth – Small – Bounces on impact

Types of precipitation

• Hail– Hail stones grow while circulating in cloud– Sizes vary– Can be destructive

Types of precipitation

• Freezing Rain– Falls as rain (liquid)– Freezes on contact with cold surface

Thanks to following people who have generously published pictures with a creative commons license:

Orographic lift … WireLizard on FlickrNimbostratus ... Cat Sidh on Flickr

Stratocumulus … Nicholas T on FlickrStratus … deadmanjones on Flickr

Altocumulus … andreas.christen on FlickrAltostratus … PiccoloNameki on Wikipedia

Cirrus … LemonSunrise on FlickrCirrostratus … Cat Sidh on Flickr

Cumulonimbus … Nicholas T on FlickrRain cloud from above … barto on Flickr

Rain … Ferran. on FlickrSnowflakes … CaptPiper on Flickr

Snowflake … adriangonsalves on FlickrSleet … Daniel Greene on Flickr

Hail … Topato on FlickrIce storm … Big Grey Mare on Flickr

Berries in ice … A.BellVersoix ice storm … Vin60 on Flickr