2. What we’ve covered since the midterm NigamWind: global systems; general circulation of the atmosphere: single cell model; three cell model; global pattern of winds and pressure systems at the surface and aloft Chp. 10 Ruiz- Barradas Air masses and fronts different type of air masses and associated weather; weather fronts; structure, weather and development of fronts Chp. 11 ZengFormation of the jet stream; formation of the polar front jet formation of the tropical jet Chp. 12 ZengPolar front theory-Bergen School cyclogenesis; developing cyclones and jet stream; upper level waves and surface storms; barotropic atmosphere; baroclinic atmosphere; vorticity; Rossby waves Chp. 12 Cartonglobal seasonal surface wind patterns; SST; ocean currents; upwelling; ocean water masses CartonAtmosphere/ocean Interactions: ENSO, Indian dipole, Atlantic variability KalnayWeather ForecastingChp 13 C. Kieu HurricanesChp. 15 C. KieuThunderstorms and tornadoes; atmospheric conditions that produce thunderstorms and tornadoes; air-mass thunderstorms; severe thunderstorms; lightning; tornadoes; Chp 14 CartonGlobal Climate Climate ChangeChp.16/17

3. Chapt 11: air masses

4. 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.) Typical winter conditions

5. 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.)

6. Conditions this morning

7. 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

11. Chapt 13: Weather forecasting

12. 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

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

15. 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

16. 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.

17. Tornadoes 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 average annual number of tornadoes observed in each state over average annual number of tornadoes per 10,000 square miles in each state

18. 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.

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

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

23. Chapt. 17: global climate

26. Chapt. 17 Climate var. & change

27. 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

28. 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

29. IPCC forecasts