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
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