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How do the clouds form?. Water Vapor Basics (names of different phase changes, latent heat) Humidity indices (there are 6 total). Saturation vapor pressure.

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Presentation on theme: "How do the clouds form?. Water Vapor Basics (names of different phase changes, latent heat) Humidity indices (there are 6 total). Saturation vapor pressure."— Presentation transcript:

1 How do the clouds form?

2 Water Vapor Basics (names of different phase changes, latent heat) Humidity indices (there are 6 total). Saturation vapor pressure increases non-linearly with temperature Two methods of achieving saturation and condensation (diabatic vs. adiabatic processes). Different types of condensation - dew, frost, fog (radiation, advection, upslope, precipitation, steam), clouds. Review of last lecture

3 The most common atmospheric circulation structure L H H L Heating Cooling or No Heating Imbalance of heating Imbalance of temperature Imbalance of pressure Wind Radiation Convection Latent/Sensible Conduction

4 Clouds Clouds are instrumental to the Earths energy and moisture balances, and constitute a wild card for climate change

5 Satellite observation of clouds NASAs International Satellite Cloud Climatology Project (ISCCP) Combine the measurements of 5 geostationary and 1-2 polar orbiting satellites. 1983-Now, cloud top height and optical depth. NASAs Earth Observation System including a set of polar orbiting satellites (A-Train), especially CloudSat (with a cloud radar) and CALIPSO (with a cloud lidar). Ongoing, cloud particle information, detailed vertical structure.

6 Global map of clouds

7 Vertical structure of clouds

8 1. Cloud top height/pressure 2. Cloud thickness (optical depth) 3. Cloud coverage When clouds comprise more than 9/10th of the sky = overcast When coverage is between 6/10th and 9/10th = broken When coverage is between 1/10th and 6/10th = scattered Cloud coverage less than 1/10th = clear Cloud Properties

9 NASAs International Satellite Cloud Climatology Project (ISCCP) Cloud Classification - commonly used in climate research

10 Clouds are both good reflectors of solar radiation (cooling effect) and good absorbers of earth emitted longwave radiation (warming effect). The net effect (cooling or warming) depends on the type of cloud In a changing climate, increases in high thin clouds would promote warming, while increases in low thick clouds would cause cooling Climate models have difficulties in simulating clouds, especially low thick clouds (stratocumulus) Conclusion: Clouds cause the largest uncertainty in model simulations of future climate. Why do clouds constitute a wildcard for climate change? Stronger warming effect Stronger cooling effect

11 Video: Convective cloud time lapse http://www.youtube.com/watch?v=kapTREk0gX ghttp://www.youtube.com/watch?v=kapTREk0gX g

12 Formation of clouds Most clouds form as air parcels in boundary layer are lifted and cooled to saturation. The air parcels could be lifted by mountains, meeting of different air masses, surface convergence, and local convection

13 Lifting by local convection Static stability – refers to atmospheres susceptibility to being displaced F B = ρ env g – ρ parcel gStability related to buoyancy force determined by density difference btw parcel and environment (F B = ρ env g – ρ parcel g) determined by temperature difference btw parcel and environment (ρ = P/TR) When an air parcel rises, the cooling rate of the parcel (adiabatic lapse rate or ALR) relative to the cooling rate of surrounding atmosphere (environmental lapse rate or ELR) determines the stability of a parcel. Environment Parcel ρ parcel g Δp/Δz=ρ env g

14 Environment Parcel Environment Parcel The three types of stability Absolutely Unstable Conditionally Unstable Environment Parcel Absolutely Stable Convection happens when: (1)boundary layer air is warm and moist (2)Environmental air above boundary layer is cold When comparing the temperature btw parcel and environment, there are 3 possible outcomes:

15 When convection happens: 1.Rising up of air parcel (called updraft) 2.Formation of clouds and sometimes precipitation 3.Heating up the environment because parcel temperature is warmer than the environment

16 1) Entrainment Turbulent mixing of ambient air into parcel Leads to evaporation along cloud boundaries Evaporation uses latent heat, cooling the cloud reduces buoyancy Courtesy Russ Dickerson, U. Maryland What stops unstable air masses from rising indefinitely ? 2) Encountering a layer of stable air (inversion) a rising parcel may reach a stable upper air environment the parcel cooling rate will exceed that of the ambient air the parcel will slowly cease ascension and come to rest at some equal temperature level three types: radiation, frontal, subsidence

17 In convection, an updraft is often associated with a downdraft – Overturning of the troposphere Air can be cooled down by radiation, evaporation of raindrops, melting of snowflakes, etc. Air that is cooler than its environment tends to sink, leading to the formation of downdrafts Sometimes precipitation drag enhances the downdrafts Downdrafts cool down the environment (generally the lower troposphere) Downdrafts (also called downbursts) can cause significant damage at the ground

18 Low stratocumulus clouds Generated by convection inside boundary layer Convection is driven by cloud-top longwave cooling and evaporative cooling

19 3 cloud properties, 9 ISCCP cloud types Why do clouds constitute a wildcard for climate change? Competition between greenhouse effect and albedo effect Convection: 3 types of stability. Two factors limiting the height of clouds Summary

20 Works cited http://www.atmos.washington.edu/2004Q2/547/www/ http://capita.wustl.edu/capita/datasets/modis/globfused/g lob3d.htmlhttp://capita.wustl.edu/capita/datasets/modis/globfused/g lob3d.html http://www.ssec.wisc.edu/sos/wvsst/wvsst.html http://www.arm.gov/news/facility/post/1025 http://apollo.lsc.vsc.edu/classes/met130/notes/chapter4/ es_temp.htmlhttp://apollo.lsc.vsc.edu/classes/met130/notes/chapter4/ es_temp.html http://www.meted.ucar.edu/oceans/currents/print.htm http://visibleearth.nasa.gov/view.php?id=57735 http://www.crh.noaa.gov/lmk/?n=downburst http://cde.nwc.edu/SCI2108/course_documents/earth_m oon/earth/earth_science/convection/convection_advectio n.htmhttp://cde.nwc.edu/SCI2108/course_documents/earth_m oon/earth/earth_science/convection/convection_advectio n.htm


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