1!Quiz Ch. 7-8 !!• What is CAPE?!• In stable air, is higher air hotter or colder than it “should be”?!• In unstable air, is higher air hotter or colder than it “should be”?!• In dry air, what variable “should be” constant (i.e. if air has neutral stability)?!• In moist/saturated air, what variable “should be” constant (i.e. if air has neutral stability)?!Answer briefly and clearly, with appropriate equations or diagrams. !Lecture Ch. 8a!• Cloud Classification!• Precipitation Processes!Curry and Webster, Ch. 8!For Wednesday, Read Ch. 12!2!Cloud Classification!10 main cloud types!1. Cirrus (Ci)!2. Cirrocumulus (Cc)!3. Cirrostratus (Cs)!4. Altocumulus (Ac)!5. Altostratus (As)!6. Nimbostratus (Ns)!7. Stratocumulus (Sc)!8. Stratus (St)!9. Cumulus (Cu)!10. Cumulonimbus (Cb)!All high clouds!Middle clouds!Grayish, block the sun, sometimes patchy!Sharp outlines, rising mounds, bright white!Cumulus Clouds!Swelling Cumulus Active heaped-up cloud with flat bottom and growing cauliflower top. [http://www.fox8wghp.com/spacious.htm]!10.2 Cumuliform Clouds!Types of cumulus!• Fair weather cumulus!– Horizontal/vertical scale = 1 km!– No precipitation!• Towering cumulus!– Horizontal/vertical scale = several km!– Frequently precipitate!• Cumulonimbus!– Vertical extension to tropopause with anvil tops!– Width = 10s of km!– Heavy precip, lightning, thunder, hail!• Mesoscale convective complex!– Aggregation of cumulonimbus (100s of km)!– Large amount of rain!– Can develop circulation pattern!Southeast Pacific!3!Cumulonimbus Clouds!Cumulonimbus Massive cloud system producing heavy showers, sometimes with hail. Most active clouds may have lightning and thunder. A few spawn tornadoes. [http://www.fox8wghp.com/spacious.htm]!10.2 Stratus Clouds!Stratus Low lying layer of cloud (called fog if on the ground) with no structure. [http://www.fox8wghp.com/spacious.htm]!10.2 Cirrus Clouds!Cirrus! An ice crystal cloud, wispy in appearance. May produce ice crystal snow in winter or in mountains. [http://www.fox8wghp.com/spacious.htm]!Altostratus Clouds!Altostratus Thickly layered water droplet cloud. Sun seen as through ground glass. [http://www.fox8wghp.com/spacious.htm]!Nimbostratus Clouds!Nimbostratus Thick layered cloud - usually dark gray. Produces continuous rain or snow over large area. [http://www.fox8wghp.com/spacious.htm]!Fog!http://www.tqnyc.org/2009/00767/fog.jpg!4!Global Cloud Distribution"Zonally averaged climatology of cloud type"Cirrus!Cumulonimbus!Altitude (km)!Latitude!Altostratus!Nimbostratus!Stratus!Cumulus!Cloud Types and Drop Sizes!• Frequency distributions of the mean cloud droplet size for various cloud types!Decoupling of Stratocumulus-Topped Boundary Layer!Drizzle evaporates, net cooling!Drizzle forms, net warming!Observations: "Varying cloudy structure!R. Wood, 11/17/10!Precipitation Processes!• Collision/coalescence (accretional growth)!Small, spherical drop!Larger, spherical drop!Largest, spherical drop!5!Larger than 3 mm, drops break up due to aerodynamic forces!Ice crystals!Larger drops are faster so they collide with the smaller drops in their way.!Whether or not the two particles stick is determined by the collection efficiency!Collection Efficiency E is the probability that a collision AND coalescence event will occur.!r/R = 0.2!Flow field around large particle will move smaller particle, lower E !r/R = 1!Inertia of collected drop increases, higher E !Drop Growth and Size!• Bigger particles (~25 micron) grow faster !Drops above this size grow and precipitate!6!Precipitation and Drop Size!• Terminal velocity increases with drop size!• Precipitation occurs when !!– terminal velocity exceeds updraft velocity!Precipitation and Cloud Type!• Precipitation depends on!– Condensed water (water and temperature)!– Updraft velocity (dynamics)!– Temperature (cold or warm processes)!– Drop size (aerosol effects)!Stochastic collection model: based on probability!10% collide (w/ drops outside this population)!10% collide (w/ drops outside this population)!Diffusion of water onto ice in water-saturated environment!Slow growth by collision/coalescence!Aggregation is slower!Collision/coalescence is faster for larger droplets!Liquid Water Path!MODIS cloud LWP, and cloud temperature, used to determine adiabatic h!PBL Clouds are thin!!Adiabatic cloud thickness of stratiform boundary layer clouds!7!Connecting this course to current research… Start from two sections of Curry & Webster: Parameterization of Cloud Microphysical Processes (Section 8.6), pages 241 - 244. Understand the ideas behind the equations on page 242 and note the remarks on page 244. Cloud-radiation Feedback (Section 13.4), especially the last 2 paragraphs of Section 13.4.1 on pages 368, 369, and the last paragraph of Section 13.4 on page 374. What do we mean by “parameterization”? Some physical processes are too poorly understood, and/or they occur on too small space and time scales, so we cannot adequately represent them in global numerical climate models. For example, clouds and cloud-radiation interactions are important to climate and to modeling climate change. We don’t know how to include these processes correctly, but we cannot afford to omit them. A working definition of “parameterization”: A parameterization is an algorithm or rule for obtaining the statistical effect, of an ensemble of small-scale processes (e. g., cloud processes), on the large-scale prognostic fields computed explicitly in a model (e. g., wind, pressure, temperature, humidity). In general, the parameterization must be explicit, in the sense that the statistical effect can be computed as a function of the large-scale variables themselves. Example: cloud fraction might be a function of humidity. First, some background. We define “climate sensitivity” as the equilibrium change in global average surface atmospheric temperature in response to doubling the present atmospheric concentration of carbon dioxide. (There are many alternative definitions). Many (but not all) reputable models have sensitivities ranging from about 1.5 deg C to 4.5 deg C. This range is an
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