MET 112 Global Climate Change - Lecture 6 Clouds and Global Climate Dr. Craig Clements San Jose...
-
date post
21-Dec-2015 -
Category
Documents
-
view
216 -
download
1
Transcript of MET 112 Global Climate Change - Lecture 6 Clouds and Global Climate Dr. Craig Clements San Jose...
MET 112 Global Climate Change - Lecture 6
Clouds and Global Climate
Dr. Craig ClementsSan Jose State University
QuestionsQuestions
What role do clouds play on the Earth’s climate?
What would happen to our climate if clouds were to increase/decrease?
Water in the atmosphereWater in the atmosphere
Definitions:
– Evaporation:
– Condensation:
– Precipitation:
Process where a liquid changes into a gasProcess where a liquid changes into a gas
Any liquid or solid water that Any liquid or solid water that falls from the atmosphere to falls from the atmosphere to the ground. (i.e. RAIN!)the ground. (i.e. RAIN!)
Process where a gas changes into a liquidProcess where a gas changes into a liquid
Water freely Water freely evaporating and evaporating and condensingcondensing
Since more water Since more water molecules are molecules are evaporating than evaporating than condensing, then condensing, then net evaporation is net evaporation is occurring.occurring.
Lid on:Lid on:
Now, evaporation Now, evaporation and condensation and condensation are equal. The air are equal. The air above water is above water is now called now called ‘saturated’.‘saturated’.
The humidity is The humidity is now 100%now 100%
CondensationCondensation
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.a. DustDustb.b. SaltSaltc.c. SmokeSmoke
Condensation occurs primarily as temperature cools:-colder the molecules more likely they are to ‘stick’ to other molecules
Clouds and radiationClouds and radiation
Cloud - Climate InteractionsCloud - Climate Interactions
Albedo effect - COOLINGAlbedo effect - COOLING Clouds reflect incoming solar radiation. Clouds reflect incoming solar radiation.
The cloud droplet size and total water content The cloud droplet size and total water content determine the overall reflectivity. determine the overall reflectivity.
Greenhouse effect - WARMINGGreenhouse effect - WARMING Clouds are good absorbers (and emitters) of long Clouds are good absorbers (and emitters) of long
wave (infrared) radiation.wave (infrared) radiation.
Indirect Effect due to aerosols (I) Certain aerosols may enhance cloud production and
character Recall how clouds form
– Water vapor condenses to liquid water– This processes requires ‘cloud condensation nuclei’– Examples of cloud condensation nuclei
Dust, salt, smoke (all of which are natural aerosols) So, aerosols (with both natural and anthropogenic origin)
– may serve as cloud condensation nuclei.
Indirect Effect due to aerosols (II)
More cloud condensation nuclei– would enhance cloud production
The question then is how would clouds change– Current understanding is that This processes would increase cloud albedoThis processes would increase cloud albedo
This idea of enhanced cloud formation by increases in aerosols is termed – The ‘indirect effect’ of aerosols
Understanding of these processes is currently incomplete.– But model results suggest more low clouds and thus
Total effect on Earth’s energy budget– Cooling– Radiative Forcing: negative– Cirrus cloud (high clouds) production possible, but still uncertain how
important.
Clouds and day to day Clouds and day to day temperaturestemperatures
Imagine that you are going camping in the Sierras Imagine that you are going camping in the Sierras with your friends. On the first day (and evening) it with your friends. On the first day (and evening) it is cloudy, while on the second day (and evening) it is cloudy, while on the second day (and evening) it is clear. Based on this information alone:is clear. Based on this information alone:
Which day would be warmer?Which day would be warmer?
Which evening would be warmer?Which evening would be warmer?
Explain your answers.Explain your answers.
Low and High cloudsLow and High clouds
Consider two types of clouds:Consider two types of clouds:
1.1. Low levels clouds Low levels clouds
2.2. High levels cloudsHigh levels clouds
Q: How is the Earth’s surface energy budget Q: How is the Earth’s surface energy budget different for low clouds compared to high different for low clouds compared to high clouds?clouds?
Clouds and climateClouds and climate
Cloud A: Low level, (dark, thick)Cloud A: Low level, (dark, thick)
Cloud B: High level, light 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
Cumulus clouds. Small cumulus clouds such as these are sometimes called fair weather cumulus, or cumulus humilis
Changes in cloudsChanges in clouds
Increases in low level clouds will:Increases in low level clouds will:– cool the surface (cooling outweighs cool the surface (cooling outweighs
warming)warming)
Increases in high level clouds will:Increases in high level clouds will:– warm the surface (warming outweighs warm the surface (warming outweighs
cooling)cooling)
Controls on ClimateControls on Climate
Seasonal temperature and precipitation patterns Seasonal temperature and precipitation patterns are generally attributable to: are generally attributable to:
LatitudeLatitude Mountains and highlandsMountains and highlands Land and water locationLand and water location Prevailing windsPrevailing winds Pressure and wind systems Pressure and wind systems Ocean currentsOcean currents
QuestionsQuestions
Indicate the warmest and coldest areas of the Indicate the warmest and coldest areas of the Earth.Earth.
Consider the temperature at 60N latitude. Indicate Consider the temperature at 60N latitude. Indicate on the map the coldest and warmest places at 60N. on the map the coldest and warmest places at 60N.
What is the temperature difference between these What is the temperature difference between these locationslocations
What factors might explain this temperature What factors might explain this temperature difference?difference?
Why is there not a similar difference seen at 60S?Why is there not a similar difference seen at 60S?
Climate controls: Climate controls: Latitude/MountainsLatitude/Mountains
LatitudeLatitude– Higher latitude climates are generally Higher latitude climates are generally
(cooler/warmer)(cooler/warmer)– Lower latitudes climates are generally Lower latitudes climates are generally
(cooler/warmer)(cooler/warmer) MountainsMountains
– Higher altitudes climate are generally Higher altitudes climate are generally (cooler/warmer): cooler temperatures(cooler/warmer): cooler temperatures
– Windward side of mountains are generally Windward side of mountains are generally (cooler/warmer) and (wetter/drier), than leeward side(cooler/warmer) and (wetter/drier), than leeward side
Climate controls: Climate controls: Latitude/MountainsLatitude/Mountains
LatitudeLatitude– Higher latitude climates are generally Higher latitude climates are generally
(cooler/warmer)(cooler/warmer)– Lower latitudes climates are generally Lower latitudes climates are generally
(cooler/warmer)(cooler/warmer) MountainsMountains
– Higher altitudes climate are generally Higher altitudes climate are generally (cooler/warmer): cooler temperatures(cooler/warmer): cooler temperatures
– Windward side of mountains are generally Windward side of mountains are generally (cooler/warmer) and (wetter/drier), than leeward side(cooler/warmer) and (wetter/drier), than leeward side
Controls on ClimateControls on Climate
Seasonal temperature and precipitation patters Seasonal temperature and precipitation patters are generally attributable to: are generally attributable to:
LatitudeLatitude Mountains and highlandsMountains and highlands Land and water locationLand and water location Prevailing windsPrevailing winds Pressure and wind systems Pressure and wind systems Ocean currentsOcean currents
Controls on Climate: OceansControls on Climate: Oceans
Ocean TemperaturesOcean Temperatures– Coasts of continents are affected by ocean Coasts of continents are affected by ocean
temperatures: Generally less temperature temperatures: Generally less temperature extremes compared to interior of continentsextremes compared to interior of continents
– Cold oceans: Cold oceans:
– Warm oceans:Warm oceans:
generally produce cooler/drier conditionsgenerally produce cooler/drier conditions
generally produce more warm/humid conditionsgenerally produce more warm/humid conditions
Controls on Climate: Controls on Climate: Pressure systemsPressure systems
Rising and sinking motion associated with low Rising and sinking motion associated with low and high pressure affects climateand high pressure affects climate
Areas where pressure seasonally low, Areas where pressure seasonally low, –
Areas where pressure seasonally high, Areas where pressure seasonally high, –
Tropics: rainyTropics: rainy
Subtropical high (30N/30S): warm and drySubtropical high (30N/30S): warm and dry
January Average sea-level Pressure and surface wind patternJanuary Average sea-level Pressure and surface wind pattern