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Chapter 9 and 10

Chapter 9 and 10. Atmosphere and Severe Weather. Energy, cont. The ability to do work Types Potential - stored energy Kinetic - energy of motion Heat - energy of random motion of atoms and molecules. Heat Transfer. Conduction Transfer through atomic or molecular interactions

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Chapter 9 and 10

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  1. Chapter 9 and 10 Atmosphere and Severe Weather

  2. Energy, cont. The ability to do work Types Potential - stored energy Kinetic - energy of motion Heat - energy of random motion of atoms and molecules

  3. Heat Transfer Conduction Transfer through atomic or molecular interactions Two bodies in contact with one another Convection Transfer through mass movement of a fluid Hot air rises displaces cool air which falls Creates a convection cell Radiation Transfer through electromagnetic waves

  4. Figure 9.3

  5. Earth’s Energy Balance A general equilibrium between incoming and outgoing radiation Earth intercepts only a fraction of the sun’s radiation Sun’s energy drives hydrologic cycle, ocean waves and currents, and global atmospheric circulation Nearly all of the energy available at Earth’s surface comes from the sun Exception, heat from Earth’s core that drives plate tectonics

  6. Heat Energy Energy transferred between two objects at different temperatures Sensible heat Heat that is monitored by a thermometer Latent heat Energy necessary to cause a change in state Example: latent heat of vaporization is energy necessary to change liquid water into water vapor

  7. Energy Behavior Redirection Reflection back to space by clouds, water, land Scattering disperses energy is many directions Transmission Energy is passed through atmosphere Absorption Alters molecules or causes them to vibrate Some of this may be re-emitted to space

  8. Energy Behavior, cont. Temperature depends on amount of energy absorbed or reflected Reflection depends on albedo Describes the reflectivity of surfaces Dark woodlands reflect 5 percent to 15 percent Light grasslands reflect 25 percent Absorption Energy that is not reflected is absorbed Different objects absorb different wavelengths Hotter objects radiate energy more rapidly and at shorter wavelengths

  9. Figure 9.4

  10. Weather/Climate • Weather- an areas short term atmospheric condition (hours and days) • Parameters use to determine atmospheric condition • Temperature • Pressure • Moisture content • Precipitation • Sunshine • Cloud cover • Wind speed and direction

  11. Climate • Climate- a region’s long-term atmospheric conditions (averages over decades) • Temperature and precipitation are the two main factors that influence climate • These two factors are influence by air circulation, latitude, altitude, and ocean currents

  12. The Atmosphere Gaseous envelope that surrounds Earth Composed mostly of nitrogen and oxygen Smaller amounts of water vapor, argon, carbon dioxide Water vapor Important for cloud formation and circulation Comes from evaporation off of Earth’s surface Humidity describes amount of moisture in atmosphere at particular temperature Relative humidity is the ratio of water vapor present to the amount that saturates the air

  13. Structure of the Atmosphere Troposphere All of Earth’s surface is within this layer Upper boundary is tropopause Temperature decreases with increasing altitude Clouds are present at the tropopause Figure 9.7

  14. Clouds Made from very small water droplets or ice crystals that condense from the atmosphere Cumulus – puffy fair weather clouds Cumulonimbus – Tall, dark storm clouds

  15. Figure 9.8

  16. Weather Processes: Atmospheric Pressure and Circulation Atmospheric pressure also called barometric pressure Weight of a column of air above a given point Force exerted by molecules on surface In the atmosphere, pressure decreases with increasing altitude Nearly all of the weight of the atmosphere is in the lower atmosphere

  17. Figure 9.10b

  18. Weather Processes: Atmospheric Pressure and Circulation, cont. 1 Changes in air temperature and air movement are responsible for horizontal changes in pressure Temperature influences pressure because cold air is more dense and exerts greater pressure on surface Global variations in temperature cause global winds At equator, air is warm and low in density Creates low pressure zones at the equator Air rises, condenses, forms clouds and rain Cooler, drier air sinks at latitudes around 30° causing deserts

  19. Weather Processes: Atmospheric Pressure and Circulation, cont. 2 Air movement can cause changes in pressure Convergence occurs when air flows in increasing pressure Divergence occurs when air flows out decreasing pressure At surface, air moves from surface high pressures (H) to low pressures (L) Air at low rises into atmosphere and then diverges in the upper atmosphere A surface low is often associated with a high aloft and vice versa Jet streams Narrow, fast moving jets of air caused by low pressures near the top of the troposphere

  20. Figure 9.12

  21. Air Circulation

  22. Figure 9.11

  23. Figure 4-11 The World’s Major Land Biomes Section 4-3 Tropical rain forest Temperate grassland Temperate forest Tundra Tropical dry forest Desert Northwestern coniferous forest Mountains and ice caps Tropical savanna Temperate woodland and shrubland Boreal forest (Taiga)

  24. Unstable Air Tendency of air is to remain in place Atmospheric stability Air parcels resist movement or return to original spot after they move In unstable air, parcels are rising until they reach air of similar temperature and density Air is unstable when lighter, warm or moist air is overlain by denser cold or dry air Some air sinks and some air rises

  25. Fronts Air masses do not mix, Fronts are the boundary between cooler and warmer air masses Cold front when cold air is moving into warm air Warm front when warm air is moving into cold air Stationary front where boundary shows little movement Occluded front where rapidly moving cooler air overtakes another cold air mass wedging warm air in between

  26. Figure 9.13

  27. Rain Shadow

  28. Hazardous Weather: Thunderstorms Most occur in equatorial regions Most common in the afternoon or evening hours in spring or summer Three conditions necessary Warm and humid air in lower atmosphere Steep vertical temperature gradient such that the rising air is warmer than the air above it Cold air over warm air Updraft must force air up to the upper atmosphere

  29. Figure 9.15

  30. Thunderstorm Development Moist air is forced upwards, cools and water vapor condenses to form cumulus clouds Cumulus stage Moisture supply and updrafts continue, clouds grow A continuous release of latent heat from condensation warms the surrounding air causing the air to rise further Expanding the cloud into colder air causes water droplets to freeze Larger snowflakes fall and melt as raindrops Large droplets grow until they cannot be supported by updrafts

  31. Thunderstorm Development, cont. Mature stage Downdrafts and falling precipitation leave the base of the cloud Updrafts and downdrafts are present Cloud continues to grow until it reaches the top of unstable atmosphere (tropopause) Storm produces heavy rain, lightning and thunder, and occasionally hail Dissipative stage Upward supply of moist air is blocked by downdrafts Thunderstorm weakens, precipitation decreases, and the cloud dissipates Most are air mass thunderstorms and do little damage

  32. Figure 9.16

  33. Severe Thunderstorms National Weather Service, classified severe if winds > 93 km (58 mi.) per hour, or hailstones > 1.9 cm (0.75 in), or generates a tornado Necessary conditions Large changes in vertical wind shear differences in wind speed and direction Greater the wind shear, the more severe the storm High water vapor content in lower atmosphere Updraft of air Dry air mass above a moist air mass

  34. Severe Thunderstorm Types Mesoscale convective systems (MCSs) Most common type Very large clusters of self-propagating storms in which downdrafts from one creates a new storm Downdrafts come together to form outflow boundaries curved lines of thunderstorms that may travel long distances Squall lines Long lines of individual storm cells common along cold fronts Updrafts form anvil-shaped clouds extending ahead of the line Downdrafts surge forward as gust front in advance of precipitation Can develop along drylines Fronts with differing moisture content

  35. Severe Thunderstorm Types, cont. Supercells Smaller than MCSs and squall lines, but more damaging Extremely violent and spawn most tornadoes Last from 2 to 4 hours Downbursts from thunderstorms can create: Derechos Strong, straight-line windstorms Wind gusts can be tornado strength Cause fallen trees, power outages, injuries, fatalities Microbursts Hazard for aviation

  36. Hail Hard, round, irregular pieces of ice originating from thunderstorms Hail moves up and down in lower part of the storm adding layers of liquid water which then freezes Cause mostly property damage http://www.youtube.com/watch?v=HPDzy5q-s1g

  37. El Nino

  38. Lightning Lightning requires the separation of different charges into different regions of a cloud. How does charge separation in clouds occur? We don’t know for certain, but we observe this: Lightning only occurs in cold clouds with supercooled droplets and temps below 5oF. Thus, the ice crystal processes responsible for precipitation in cold clouds likely plays an critical role in charge separation.

  39. Charge Separation: One Theory Hailstones are covered by a layer of liquid water. The thin layer of liquid is positively charged. When hailstones and ice crystals collide, some of liquid molecules stick to the ice crystals. Along with the mass transfer, positive ions transfer from the hailstones to the ice crystals. The heavier, negative hail falls to cloud bottom. The lighter, positive ice crystals drift to cloud top. Produces negative lower, positive upper cloud.

  40. Charge Separation + • Top of cloud top has a positive charge. • Lower and middle of cloud has a negative charge. • Charge separation in cloud maintains the earth’s fair weather electric field denoted by the arrow E • E points toward positive polarity Polarization E – Williams, The Weather Book

  41. Lightning Stroke Ground strikes are usually negative, that is electrons flow from cloud to ground. Williams, The Weather Book

  42. Types of Discharges www://thunder.msfc.nasa.gov/

  43. http://video.nationalgeographic.com/video/environment/environment-natural-disasters/landslides-and-more/lightning/http://video.nationalgeographic.com/video/environment/environment-natural-disasters/landslides-and-more/lightning/

  44. Lightning Safety Williams, The Weather Book

  45. Hazardous Weather: Tornadoes Usually spawned by severe thunderstorms 1992–2002, killed 57 people/year Defined by vortex extending downward from the cloud and touching the ground Called funnel clouds when it does not touch ground Form where there are large differences in atmospheric pressure over short distances Figure 9.18b

  46. Tornado Development—Organizational Stage Vertical wind shear causes rotation to develop within the storm Strong updrafts in advance of the front tilt the horizontally rotating air vertically Known as a mesocyclone Updrafts at rear of the storm lower part of the cloud Wall cloud Wall cloud rotates and funnel descends

  47. Figure 9.19

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