Clouds Textbook Section 18.2 Irondale High School Earth Science Clouds are collections of billions of ice crystals, water droplets, or combination of the two At temperatures above freezing, a cloud consists of small water droplets At temperatures below freezing, a cloud consists of tiny ice crystals and/or super cooled water drops Naming/Classifying Clouds Clouds almost always form in upward moving air they are natures way of painting updrafts! (Remember that water vapor is invisible!) Clouds are named according to their: Height above ground level Shape High Clouds Cloud Heights Above 7,000 meters (~23,000 feet) Cirrus or a prefix Cirro used to name these Middle Clouds 2,000 7,000 meters (~6,600 ~23,000 feet) Prefix Alto used to name these Low Clouds Below 2,000 meters (~6,600 feet)
Cloud Shapes Stratiform Clouds: Clouds that form horizontally in layers Stratus, or prefix Strato used to name Cumuliform Clouds: Clouds that grow vertically, and are puffy Cumulus, or prefix Cumulo used to name Image from: http://www.centennialofflight.gov/2003ff/clues/clipart/stratus.jpg Clouds Producing Precipitation These clouds are named with the prefix nimbo or the suffix nimbus depending on the specific cloud type http://www.wmo.int/pages/mediacentre/news/archive/images/monsoon_rain.jpg Image from: http://images.usatoday.com/weather/photos/clouds/cumulus.jpg http://www.ucar.edu/educ_outreach/webweather/cloud3.html http://www.free online private pilot groundschool.com/images/cloud types.gif
Cloud Example #1 Cloud Example #2 Puffy, cotton ball like fair weather cloud Vertical development Cumulus! Flat, layered Low Producing Precipitation Nimbostratus! http://mapmaker.meteor.wisc.edu/~jbr unner/ackerman/smclouds/nimbostratus.gif http://www.meteonet.org/assets/images/cumulus.jpg Cloud Example #3 Cloud Example #4 Mid level cloud Puffy characteristics Altocumulus! High cloud Composed entirely of ice crystals Thin, wisplike strands Cirrus! http://www.freewebs.com/thomp730/cirrus%20clouds Horz.jpg http://www.windows.ucar.edu/php/gallery/gallery.php?id=32
High Cloud Puffy in nature Composed of ice crystals Cirrocumulus! Cloud Example #5 Mid level cloud Flat in shape Altostratus! Cloud Example #6 http://i.pbase.com/v3/59/307059/2/48991673.5926fs.jpg http://quest.arc.nasa.gov/aero/virtual/demo/weather/tutorial/altostratus.html Cloud Example #7 Very tall, summer cloud Produces precipitation Is also known as a thunderhead Can extend to the top of the troposphere Anvil top Cumulonimbus! http://upload.wikimedia.org/wikipedia/commons/8/82/wagga Cumulonimbus.jpg Another Cumulonimbus over Africa as Viewed from Space http://www.allamericanpatriots.com/photos/cumulonimbus cloud over africa http://faculty.ksu.edu.sa/kolibi/pictures%20library/24gr_cumulonimbus%5b1%5d.jpg
High cloud composed entirely of ice crystals Thin and flat in shape May often produce a halo effect around sun or moon Cirrostratus! Cloud Example #8 http://content.answers.com/main/content/wp/en/thumb/d/d1/300p x Cirrostratus02.jpg Low clouds Relatively horizontal, yet mildly puffy in shape Stratocumulus! Cloud Example #9 http://farm1.static.flickr.com/107/292945969_3289550df5.jpg?v=0 Cloud Formation In order for clouds to form, there needs to be: 1. Water vapor present in the air (this is invisible) 2. Cooling of the air temperature to the dew point (often through expansion of rising air) air is now saturated 3. Particles in the air for the water vapor to condense onto known as CCN (Cloud Condensation Nuclei) The Condensation Level From text page 398
Instability/Stability Finding Cloud Base (Condensation Level) From text page 399 From text page 401 Cloud Base Height Calculations Dew Point drops at a rate of 2 C per 1000m rise Air Temperature drops at a rate of 10 C per 1000m rise In other words the dew point and temperature approach each other at a rate of 8 C for every 1000m of rise Cloud Base Height Calculations So as the air rises, temperature & dew point, with an original spread of 8 C, would become equal (form a cloud) at 1000m Spread in Temperature ( C) 8 16 24 32 Cloud Base Height (m) 1000 2000 3000 4000
Cloud Base Height Calculations Or think of it this way what if we look at it as how many meters high will a cloud form, per 1 C of difference between temperature and dewpoint? 1000m/8 C = 125m So (Temperature Dew Point) x 125 = Cloud Base Height (with temperatures in celsius and height in meters)