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 stops You all stand still When the wind blows You walk away slow. White sheep, white sheep, Where do you go?

A good repository of cloud photos in various categories can be found at

Questions  What role do clouds play on the Earth’s climate?  What would happen to our climate if clouds were to increase/decrease?

Earth System Water Cycle

6 MET 112 Global Climate Change

Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condensesdew into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. Clouds Formation

8 MET 112 Global Climate Change Video  videos/MET%20112%20Video%20Library- MP4/clouds/ videos/MET%20112%20Video%20Library- MP4/clouds/ Clouds Formers –clouds and aerosols

CLOUDS: A visible mass of liquid water droplets suspended in the atmosphere above Earth's surface. 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:

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 liquid

Water freely evaporating and condensing

Since more water molecules are evaporating than condensing, then net evaporation is occurring.

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: a. Dust b. Salt c. 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 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 same

Which evening would be warmer? 1.First day (clear) 2.Second day (cloudy) 3.Both the same

Clouds types

Low 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) (sub visible or thin)

Clouds and climate Cloud A: Low level, (dark, thick) Cloud B: High level, light (sub visible or thin) (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)

Cirrus

Altocumulus (possibly cirrocumulus, depending on altitude of the clouds)

Stratocumulus

Broken stratocumulus

Nimbostratus

Cumulus humilis (commonly called 'fair weather cumulus')

Cumulus

Cumulonimbus

Stratus

Cirrus

Clouds That Look Like Things

Explain how the earth’s climate would change as a result of aircraft contrails.

Class Participation Concept Map

Activity : Water Concept Map Draw a concept map using the following terms. You may add additional terms if you wish. Water vapor Ice Liquid water Condensation Evaporation Gas High Cloud Low Cloud Precipitation Condensation nuclei Temperature Warming Cooling Air