Week 8 Notes

1. Week 8 Notes • Tonight (Oct 12) • Airmasses and Fronts (Chp 8) • El Niño Classwork (HW#7) • El Niño and La Niña • Next Week (Oct 19) • Mid-Latitude Cyclonic Storms • Remote Sensing • Review for Midterm #2 • Oct. 26 – MIDTERM #2 • Guest Speaker – Julie Watts, KPIX • Term Paper Outlines Due

2. Week 8 Notes • Tonight (Oct 12) • Airmasses and Fronts (Chp 8) • El Niño Classwork (HW#7) • El Niño and La Niña • Next Week (Oct 19) • Mid-Latitude Cyclonic Storms • Remote Sensing • Review for Midterm #2 • Oct. 26 – MIDTERM #2 • Guest Speaker – Julie Watts, KPIX • Term Paper Outlines Due

4. CHAPTER 9 AIR MASSES AND FRONTS

5. Air Masses and Fronts

6. Air Mass Development Semi-permanent circulation patterns provide consistent wind patterns and breeding grounds for air masses.

7. Air Mass Properties • Take on the properties of the underlying surface • Characterized by Temperature and Humidity • Classified by location of “origin” • Geographically • Tropical • Polar • Arctic • Surface Properties • Maritime • continental • Characteristics more prevalent if air mass remains over source region for a long period

8. Air Mass Properties Fig. 9.1, p. 238

9. Air Mass Classifications • cP - continental Polar • Cold, dry, stable • Extremely cold cP air mass may be designated cA (continental Arctic) • mP - maritime Polar • Cool, moist, unstable • mT - maritime Tropical • Warm, moist, usually unstable • cT - continental Tropical • Hot, dry • Stable air aloft, unstable surface air • cA – continental Arctic

10. Air Mass Source Regions

11. Continental Polar (cP) • Cold, Dry • Develops over the interior of • North America -- Central Canada -- Siberia Arctic Air (cA) • Bitterly Cold and Very Dry • Develops over the snow or ice usually north of 60° N

12. Marine Polar (mP) • Cold, Moist • Source: Cold ocean waters of the North Pacific and North Atlantic • Major type for storms to affect N. California and the Pacific NW • Responsible for fueling “Nor-easters”

13. Tropical (T) • Continental Tropical (cT) • Hot, Dry • Source: Deserts of Mexico and the SW United States • Very unstable because of heat and convection, but cloudless because of lack of moisture. • Marine Tropical (mT) • Warm, Humid • Source: Tropical and subtropical oceans and the Gulf of Mexico

14. United States Air Masses

15. Example Air Masses cP mT

16. Air Mass Invasion

17. Air Mass Modification • Air masses eventually move • If it moves over a region different from where it originated, the air mass will be modified, by the land that the air is travelling over. • Changes: warming, cooling, adding or reducing moisture content

18. Air Mass Modification cP The cP air mass will be warmed by the warmer land that it passes over. Warmer Land

19. Air Mass Modification • Originates as cP air from Asia and is carried across the Pacific becoming mP Stepped Art Fig. 9.8, p. 245

20. Lake Effect Snow

21. Fronts • Fronts • Narrow transition zone between air masses of differing densities. • The density differences usually arise from temperature differences. • Density differences may be a result of humidity differences (summer). • A front is the boundary or transition zone between different air masses.

22. Frontal Symbols

23. Cold Front • Cold Front • Boundary with a colder (more dense) airmass advances and displaces the warmer (less dense) air. • The largest temperature differences are normally associated with cold fronts. • Average speed ≈ 30 mph • Temperatures drop rapidly

24. Cold Front • Precipitation: Located on either side of the front. • Convective, showery in nature

25. Warm Front • Warm Front • Colder (more dense) air retreats and is replaced by the warmer (less dense) air. • Warm fronts tend to have weaker temperature gradients. • Average speed ≈ 16 mph • Temperatures slowly rise

26. Warm Front • Lifted warm air produces widespread clouds and precipitation well in advance of boundary

27. Occluded Front • Cold fronts typically move faster than warm fronts. • Cold fronts can catch up and “overtake” a warm front. • Two types of occlusions: • Cold type occlusion • Warm type occlusion (very rare)

28. Occluded Front

29. What kind of front is it? • From the vantage point of the ground… • If warm air replaces colder air, the front is a warm front • If cold air replaces warmer air, the front is a cold front • If the front does not move, it is a stationary front • Occluded fronts do not intersect the ground; the interface between the air masses is aloft

31. El Niño, La Niña and Other Climate Variables

32. Classwork: El Niño Pre-Test (HW#7) Divide into 6 groups. Discuss and choose a spokesperson to present a few comments from then group. THIS IS A CLOSED BOOK/COMPUTER EXERCISE. Turn in a sheet for each group with last names. What is El Niño? Where does El Nino occur? What impact does El Niño have on California? Does it impact other parts of the world? What is La Niña? Is there currently an El Niño, La Niña or neither?

34. Ripped from the Headlines… El Niño Myths • El Niño will be coming to California again • All El Niños are the same • El Niño spawns storms • El Niño means lots of rain for California • El Niño means flooding and big waves for California

35. Normal

36. El Niño

37. El Niño Fig. 14.13, p. 418

38. El NiñoStorm Track Pattern

39. Worldwide El Niño Impacts

40. La Niña

41. La NiñaStorm Track Pattern

42. Worldwide La Niña Impacts

43. Southern Oscillation • Pressure Difference between Darwin and Tahiti • Discovered by Gilbert Walker in 1924 • “Tropical See-Saw” • Negative SOI closely related to El Niño • ENSO = El Niño Southern Oscillation

44. Oceanic Niño Index (ONI) • SST departures from average Niño 3.4 SST • 3-month running mean values of SST departures

45. El Niño: ONI ≥ +0.5°CLa Niña: ONI ≤ - 0.5°C

46. List of ENSO Events 5 Consecutive months of criteria

47. All El Niños

48. All El Niños

49. Weak El Niño

50. Weak El Niño