MET 112 Global Climate Change -. CLOUDS and CLIMATE. Prof. Menglin Jin Department of Meteorology, San Jose State University. Outline Clouds Formation Clouds Climatology. Clouds and the Radiation Budget. Clouds by Christina Rossetti
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MET 112 Global Climate Change - CLOUDS and CLIMATE Prof. Menglin Jin Department of Meteorology, San Jose State University Outline Clouds Formation Clouds Climatology Clouds and the Radiation Budget
Clouds by Christina Rossetti White sheep, white sheep,On a blue hill,When the wind stopsYou all stand stillWhen the wind blowsYou walk away slow.White sheep, white sheep,Where do you go?
A good repository of cloud photos in various categories can be found at www.cloudappreciationsociety.org/gallery
Questions • What role do clouds play on the Earth’s climate? • What would happen to our climate if clouds were to increase/decrease?
Clouds Formation 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 visible mass of liquid water droplets suspended in the atmosphere above Earth's surface. http://earthobservatory.nasa.gov/Library/glossary.php3 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 Process where a gas changes into a liquid Any liquid or solid water that falls from the atmosphere to the ground. (i.e. RAIN!)
Water freely evaporating and condensing Since more water molecules are evaporating than condensing, then net evaporation is occurring.
Lid on: The humidity is now 100%
Lid on: Now, evaporation and condensation are equal. The air above water is now called ‘saturated’. The humidity is now 100%
Condensation • 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: • Dust • Salt • Smoke • Condensation occurs primarily as temperature cools: • colder the molecules more likely they are to ‘stick’ to • other molecules
Zonal Mean Cloud Effective Radius(M. D. King, S. Platnick et al. – NASA GSFC) July 2006 (Collection 5) Aqua
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 cloudy, while on the second day (and evening) it is clear. Based on this information alone: Which day would be warmer? Which evening would be warmer? Explain your answers.
0 of 70 Which day would be warmer? • First day (clear) • Second day (cloudy) • Both the same
0 of 70 Which evening would be warmer? • First day (clear) • Second day (cloudy) • Both the same
Low and High clouds Consider two types of clouds: • Low levels clouds • 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 earth
Changes 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)
Explain how the earth’s climate would change as a result of aircraft contrails.
Questions • What percentage of the sun’s radiation is • absorbed by the Earth’s surface? • absorbed by the atmosphere • reflected out to space? • If the sun’s radiation was to increase by 10%, how would the following energy units change (increase, decrease or stay the same) • Energy gained by the Earth’s surface. • Energy lost by the Earth’s surface. • Energy emitted by greenhouse gases. • Energy lost to space.
0 of 70 What percentage of the Sun’s radiation is absorbed by the Earth’s surface? • 19% • 51% • 70% • 117%
0 of 70 What percentage of the Sun’s radiation is absorbed by the Earth’s atmosphere? • 19% • 51% • 70% • 117%
0 of 70 What percentage of the sun’s radiation is reflected out to space? • 19% • 30% • 64% • 70% • 111%
0 of 70 If the Sun’s radiation was to increase by 10%, how would the energy gained by the earth’s surface change? • Increase • Decrease • Stay the same