Ocean Currents and Weather Systems - Exam Review

1. EXAM REVIEW SLIDES:

2. Average position and extent of the major surface ocean currents. Cold currents are shown in blue; warm currents are shown in red.

3. REVIEW SLIDES: A thermal circulation produced by the heating and cooling of the atmosphere near the ground. The H’s and L’s refer to atmospheric pressure. The lines represent surfaces of constant pressure (isobaric surfaces), where 1000 is 1000 millibars.

4. The idealized wind and surface-pressure distribution over a uniformly water-covered rotating earth. http://www.youtube.com/watch?v=Ye45DGkqUkE

5. Coastal Upwelling Ekman transport moves surface seawater offshore. Cool, nutrient-rich deep water comes up to replace displaced surface waters. Example: U.S. West Coast

6. A weather map showing surface pressure systems, air masses, fronts, and isobars (in millibars) as solid gray lines. Large arrows in color show air flow. (Green-shaded area represents rain; pink-shaded area represents freezing rain and sleet; white-shaded area represents snow.)

7. A vertical view of the weather across the cold front in the previous slides along the line X–X´. (active figure!)

8. Surface weather associated with a typical warm front. A vertical view along the dashed line P-P′ is shown in the next slide. (Green-shaded area represents rain; pink-shaded area represents freezing rain and sleet; white-shaded area represents snow.)

9. Vertical view of clouds, precipitation, and winds across the warm front in the previous slide along the line P–P′. http://www.youtube.com/watch?v=huKYKykjcm0&feature=related

10. Part I • Growth and Development of ordinary Cell Thunderstorms • Thunderstorm Electrification (Lightning) • Part II • Tornadoes Thunderstorms Chapter 10

11. Simplified model depicting the life cycle of an ordinary thunderstorm that is nearly stationary. (Arrows show vertical air currents. Dashed line represents freezing level, 0°C isotherm.)

12. A simplified model describing air motions and other features associated with an intense multicell thunderstorm that has a tilted updraft. The severity depends on the intensity of the storm’s circulation pattern. http://www.youtube.com/watch?v=bOfOA3PTghM&feature=related Thunderstorms Video

13. When a thunderstorm’s downdraft reaches the ground, the air spreads out forming a gust front.

14. Radar image of an outflow boundary. As cool (more-dense) air from inside the severe thunderstorms (red and orange colors) spreads outward, away from the storms, it comes in contact with the surrounding warm, humid (less-dense) air, forming a density boundary (blue line) called an outflow boundary between cool air and warm air. Along the outflow boundary, new thunderstorms often form.

15. A Doppler radar composite showing a prefrontal squall line extending from Indiana southwestward into Arkansas. Severe thunderstorms (red and orange colors) associated with the squall line produced large hail and high winds during October, 2001.

16. Pre-frontal squall-line thunderstorms may form ahead of an advancing cold front as the upper-air flow develops waves downwind from the cold front.

17. BONUS SLIDES: Supercells A supercell thunderstorm with a tornado sweeps over Texas.

18. BONUS SLIDES: Supercells Some of the features associated with a classic tornado-breeding supercell thunderstorm as viewed from the southeast. The storm is moving to the northeast.

19. BONUS SLIDES: Supercells A wall cloud photographed southwest of Norman, Oklahoma.

20. Chapter 10 Lightning The lightning stroke can travel in a number of directions. It can occur within a cloud, from one cloud to another cloud, from a cloud to the air, or from a cloud to the ground. Notice that the cloud-to-ground lightning can travel out away from the cloud, then turn downward, striking the ground many miles from the thunderstorm. When lightning behaves in this manner, it is often described as a “bolt from the blue.”

21. When the tiny colder ice crystals come in contact with the much larger and warmer hailstone (or graupel), the ice crystal becomes positively charged and the hailstone negatively charged. Updrafts carry the tiny positively charged ice crystal into the upper reaches of the cloud, while the heavier hailstone falls through the updraft toward the lower region of the cloud.

22. The generalized charge distribution in a mature thunderstorm.

23. The development of a lightning stroke. (a) 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.

24. Time exposure of an evening thunderstorm with an intense lightning display near Denver, Colorado. The bright flashes are return strokes. The lighter forked flashes are probably stepped leaders that did not make it to the ground. http://www.youtube.com/watch?v=H_MG__53wsM Lightning Strikes Video

25. The average yearly number of lightning flashes per square kilometer based on data collected by NASA satellites between 1995 and 2002. (NASA)

26. Chapter 10 Tornadoes Tornado incidence by state. The upper # shows the average annual number of tornadoes observed in each state from 1953–2004. The lower # is the average annual number of tornadoes per 10,000 square miles in each state during the same period. The darker the shading, the greater the frequency of tornadoes. (NOAA)

27. A devastating tornado about 200 meters wide plows through Hesston, Kansas, on March 13, 1990, leaving almost 300 people homeless and 13 injured. http://www.youtube.com/watch?v=-K-z-mZ9Va4&feature=related Inside the Tornado Video

28. Average number of tornadoes during each month in the United States.

29. The total wind speed of a tornado is greater on one side than on the other. When facing an on-rushing tornado, the strongest winds will be on your left side.

30. BONUS SLIDES: Supercells (a) A spinning vortex tube created by wind shear. (b) The strong updraft in the developing thunderstorm carries the vortex tube into the thunderstorm, producing a rotating air column that is oriented in the vertical plane.

31. End

32. BONUS SLIDES: Supercells Conditions leading to the formation of severe thunderstorms, and especially supercells. The area in yellow shows where supercell thunderstorms are likely to form.

33. BONUS SLIDES: Supercells A 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.

34. BONUS SLIDES: Supercells A simplified view of a supercell thunderstorm with a strong updraft and downdraft, forming in a region of strong wind speed shear. Regions beneath the supercell receiving precipitation are shown in color: green for light rain, yellow for heavier rain, and red for very heavy rain and hail.

35. BONUS SLIDES: Tornado A powerful multi-vortex tornado with three suction vortices.