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What we’ve covered since the midterm

What we’ve covered since the midterm. Chapt 11: air masses. Typical winter conditions.

dwayne
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What we’ve covered since the midterm

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  1. What we’ve covered since the midterm

  2. Chapt 11: air masses

  3. Typical winter conditions invasion of cold, moist mP air into the mid-Atlantic and New England states. (Green-shaded area represents light rain and drizzle; pink-shaded region represents freezing rain and sleet; white-shaded area is experiencing snow.)

  4. Cold-occluded front The faster-moving cold front (a) catches up to the slower-moving warm front (b) and forces it to rise off the ground (c). (Green-shaded area in (d) represents precipitation.)

  5. Conditions this morning

  6. Chapt 12: Cyclogenisis • Topic: Jet Streaks and Storms • Entrance and exit regions associated with divergence and convergence, right exit allows divergence. • Conveyor Belt Model: air constantly glides through storm; warm, cold, and dry conveyor belt

  7. Chapt 13: Weather forecasting

  8. Weather Forecasting Methods • NWP • Types of Forecasts • Now cast <6 hrs • Short range 12-65 hrs • Medium range 3-8.5 days • Long Range >8.5 days • Accuracy and Skill • 12-24 hrs most accurate, 2-5 days good • Skill = more accurate than a forecast utilizing persistence of climatology • Other Forecasting Techniques • Persistence • Trend • Analogue • Statistical • Weather type • climatological

  9. Chapt. 14: thunderstorms & tornadoes Simplified model depicting the life cycle of an ordinary cell thunderstorm

  10. Thunderstorms • Multi-cell Thunderstorms • Thunderstorms that contain a number of convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top • Gust Front: leading edge of the cold air out-flowing air; shelf cloud, roll cloud, outflow boundary • Micro-bursts: localized downdraft that hits the ground and spreads horizontally in a radial burst of wind; wind shear, virga

  11. Lightning When the negative charge near the bottom of the cloud becomes large enough to overcome the air’s resistance, a flow of electrons — the stepped leader — rushes toward the earth. (b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, such as trees, buildings, and even humans. (c) When the downward flow of electrons meets the upward surge of positive charge, a strong electric current — a bright return stroke — carries positive charge upward into the cloud.

  12. Tornadoes average annual number of tornadoes observed in each state over average annual number of tornadoes per 10,000 square miles in each state • Tornado Occurrence • US experiences most tornadoes • Tornado Alley (warm, humid surface; cold dry air aloft) • Highest spring, lowest winter • Tornado winds • Measurement based upon damage after storm or Doppler radar • For southwest approaching storms, winds strongest in the northeast of the storm, 220 kts maximum • Multi-vortex tornados • Enhanced Fujita Scale

  13. classic tornadic supercell thunderstorm showing updrafts and downdrafts, along with surface air flowing counterclockwise and in toward the tornado. The flanking line is a line of cumulus clouds that form as surface air is lifted into the storm along the gust front.

  14. Chapt 15: hurricanes Intense storm of tropical origin with winds greater than 64kts; typhoon, cyclone, tropical cyclone Eye Eye wall Spiral rain band Anticyclonic divergence

  15. Required environmental conditions • light wind • 26.5°C sea surface temperatures (June-November) • Surface converge trigger (tropical wave) • Coriolis effect: 5-20º latitude • Tropical Disturbance • Tropical Depression (22-34kts) • Tropical Storm (35-64kts) • Hurricane (> 65kts)

  16. Chapt. 17: global climate

  17. Chapt. 17 Climate var. & change

  18. Possible Causes of Climate variability • Plate Tectonics and Mountain Building • Theory of plate tectonics • Ridge and subduction • Mountain interaction with airflow and ocean currents • Changes in ocean circulation • Variations in Solar Output • Variation on the Earth’s Orbit • Milankovitch Theory • Eccentricity • Precession • Obliquity

  19. Global Warming • Radiative Forcing • Any change in average net radiation that occurs at the top of the atmosphere which is due to some change in the climate system is called radiative forcing. • Climate Models and Recent Temperature • It is difficult to unequivocally prove greenhouse forcing due to the noise in the system. • Model well sulfate aerosols, greenhouse gases, change in solar radiation

  20. IPCC forecasts

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