MET 112 Global Climate Change - CLOUDS and CLIMATE Prof. Menglin Susan Jin Department of Meteorology, San Jos State University Outline Clouds Formation Clouds Climatology Clouds and the Radiation BudgetClouds by Christina Rossetti White sheep, white sheep, On a blue hill, When the wind stops You all stand still When the wind blows You walk away slow. White sheep, white sheep, Where do you go?Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. A Scientists’ view of Clouds CLOUDS: A visible mass of liquid water droplets suspended in the atmosphere above Earth's surface. http://earthobservatory.nasa.gov/Library/glossary.php3A good repository of cloud photos in various categories can be found at www.cloudappreciationsociety.org/gallery5 MET 112 Global Climate Change Video: cloud formation in Tucson  http://www.youtube.com/watch?v=NiCSk1zxMEs Timelapse of Tucson cloud formationsQuestions  What role do clouds play on the Earth’s climate?  What would happen to our climate if clouds were to increase/decrease?  How does clouds formation change with pollution?7 MET 112 Global Climate Change Video  http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/clouds/ DTS-5.mp4 Clouds-1.mp4 –clouds and aerosols8 MET 112 Global Climate Change Clouds Roles - Importance of Clouds  Clouds is part of hydrological cycle to move water  Clouds is key in energy – Clouds absorb/reflect short wave radiation (clouds alebedo effect) – Clouds emit longwave radiation back to space – clouds absorb surface longwave radiation and keep the heat in the atmosphere to warm the surface (clouds greenhouse effect)Earth System Water Cycle100% of the incoming energy from the sun is balanced by 100% percent total energy outgoing from the earth. incoming energy from the Sun = outgoing energy from the Earth.11 MET 112 Global Climate Change since the Earth is much cooler than the Sun, its radiating energy is much weaker (long wavelength) infrared energy. energy radiation into the atmosphere as heat, rising from a hot road, creating shimmers on hot sunny days. The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. So, the Earth maintains a stable average temperature and therefore a stable climate. http://www.srh.noaa.gov/jetstream//atmos/energy.htmClouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. Clouds Formation CLOUDS: A visible mass of liquid water droplets suspended in the atmosphere above Earth's surface. http://earthobservatory.nasa.gov/Library/glossary.php315 MET 112 Global Climate Change Water freely evaporating and condensing Since more water molecules are evaporating than condensing, then net evaporation is occurring.Clouds can form along warm and cold fronts, where air flows up the side of the mountain and cools as it rises higher into the atmosphere, and when warm air blows over a colder surface, such as a cool body of water.Water in the atmosphere  Definitions: – Evaporation: – Condensation: – Precipitation: Process where a liquid changes into a gas Any liquid or solid water that falls from the atmosphere to the ground. (i.e. RAIN!) Process where a gas changes into a liquidCondensation  The process by which water vapor changes to a cloud droplet  Water vapor molecules may ‘stick’ to condensation nuclei and grow (billions) to eventually form cloud droplet.  Examples of condensation nuclei include: a. Dust b. Salt c. Smoke  Condensation occurs primarily as temperature cools: -colder the molecules more likely they are to ‘stick’ to other molecules21 MET 112 Global Climate Change Aerosols Affect Cloud Droplet Size CCN 1.Aerosols serve as cloud condensation nuclie (CCN) CCN 2. More aerosols, they will compete for water vapor to condense on, so smaller cloud droplet Ocean case Land caseZonal Mean Cloud Effective Radius (M. D. King, S. Platnick et al. – NASA GSFC) July 2006 (Collection 5) Aqua Why ocean has larger cloud droplets than land?Clouds and radiation Cloud - Climate Interactions Albedo effect - COOLING  Clouds reflect incoming solar radiation.  The cloud droplet size and total water content determine the overall reflectivity. Greenhouse effect - WARMING  Clouds are good absorbers (and emitters) of long wave (infrared) radiation.Clouds and day to day temperatures Imagine that you are going camping in the Sierras with your friends. On the first day (and evening) it is clear, while on the second day (and evening) it is cloud. Based on this information alone: Which day would be warmer? Which evening would be warmer? Explain your answers.Which day would be warmer? 1. First day (clear) 2. Second day (cloudy) 3. Both the sameWhich evening would be warmer? 1. First day (clear) 2. Second day (cloudy) 3. Both the sameClouds typesLow and High clouds Consider two types of clouds: 1. Low levels clouds 2. High levels clouds Q: How is the Earth’s surface energy budget different for low clouds compared to high clouds?Clouds and climate Cloud A: Low level, (dark, thick) Cloud B: High level, light (sub visible or thin) Excellent reflector of incoming radiation; good absorber/emitter of infrared radiation Fair/poor reflector of incoming radiation; good/excellent absorber/emitter of infrared radiation  So, clouds both warm and cool the earth.  Overall, though, clouds act to cool the earthChanges in clouds  Increases in low level clouds will: –  Increases in high level clouds will:Changes in clouds  Increases in low level clouds will: – cool the surface (cooling outweighs warming)  Increases in high level clouds will: – warm the surface (warming outweighs cooling)CirrusAltocumulus (possibly cirrocumulus, depending on altitude of the clouds)StratocumulusBroken stratocumulusNimbostratusCumulus humilis (commonly called 'fair weather cumulus')CumulusCumulusCumulusCumulusCumulonimbusStratusStratusCirrusClouds That Look Like ThingsExplain how the earth’s climate would change as