AOSS 401, Fall 2006 Lecture 19 October 26 , 2007

1. AOSS 401, Fall 2006Lecture 19October 26, 2007 Richard B. Rood (Room 2525, SRB) rbrood@umich.edu 734-647-3530 Derek Posselt (Room 2517D, SRB) dposselt@umich.edu 734-936-0502

2. Class NewsOctober 26, 2007 • Homework • Homework 5 posted today • Includes a programming assignment that will be posted this afternoon/evening • Focus your attention on question 1

3. Today • Bring together physical concepts and preview the rest of the course • Material from Chapter 6 • Middle Latitude Structure • Quasi-geostrophic theory

4. Flow over a mountain rangeWest to East

5. What is happening with planetary vorticity?(In the (east-west, north-south) plane) Depth, H Depth, H +ΔH Depth, H +ΔH Depth, H -ΔH n f is greater for deflections to north f is less for deflections to south f + ζ is less than earth’s vorticity and wants to turn north. Arrives here wanting vorticity. “Overshoots” s west east

6. Flow over a mountain rangeEast to West

7. What is happening with planetary vorticity?(In the (east-west, north-south) plane) Depth, H Depth, H +ΔH Depth, H +ΔH Depth, H -ΔH n Flow from east planetary and relative vorticity interact together, no overshoot or undershoot. s west east

8. Wind and geopotential 200 hPa Note: Troughs associated with mountain ranges, continents

9. Observations of the Atmosphere • Vorticity • Small scale flow • Large-scale flow • Large scale flow and the climate system • Heat transport • Jet streams • Development of mid-latitude cyclones

10. Vorticity on Small Scales • From the southern California fires: http://video.nbc11.com/player/?id=171454 • What is the cause? http://aoss-web.engin.umich.edu/class/aoss102/tools/swf/?url=class/aoss102/tools/swf/

11. Vorticity on Large Scales • Remember, vorticity is caused by • Wind shear • Rotation in the flow • Can we identify these on weather maps? • (The following maps come from http://www.aos.wisc.edu/weather/)

12. 300 mb Wind Speed

13. Where is there positive vorticity?

14. 500 mb Vorticity

15. Thermal Wind • Remember, thermal wind relates • Vertical shear of geostrophic wind • Horizontal temperature gradients • Can we identify these on weather maps?

16. Where are the strongest ?

17. 850 mb Temperature

18. Convergence/Divergence • Remember, vertical motion on large scales directly related to • Convergence/divergence of ageostrophic wind • Curvature in the flow • Can we identify these on weather maps?

19. Where are surface lows/highs?

20. Surface Precipitation

21. 850 mb Temperature

22. Concepts • Vorticity: shear and curvature • Why is curvature vorticity (as opposed to shear vorticity) usually associated with developing low pressure systems? • Divergence and convergence and location of surface high and low pressure systems • Thermal wind—vertical shear of the horizontal wind and horizontal temperature gradients

23. Concepts • Features commonly found together • Jet stream • Upper level positive vorticity • Fronts • Midlatitude cyclones (low pressure systems) • Coincidence? • More on this later…

24. Large scale flow and the climate system

25. Transfer of heat north and south is an important element of the climate at the Earth’s surface. Redistribution by atmosphere, ocean, etc. Top of Atmosphere / Edge of Space Large scale weather systems transport large quantities of thermal energy from equator toward the poles CLOUD ATMOSPHERE heat is moved to poles cool air moved towards equator cool air moved towards equator SURFACE This is a transfer. Both ocean and atmosphere are important!

26. Hurricanes and heat

27. Hurricanes and heat

28. Mid-latitude cyclones

29. Mid-latitude cyclones & Heat

30. Mid-latitude Cyclones & Jet Stream

31. An estimate of the January mean temperature mesosphere stratopause note where the horizontal temperature gradients are large stratosphere tropopause troposphere south summer north winter

32. An estimate of the January mean zonal wind note the jet streams south summer north winter

33. An estimate of the July mean zonal wind note the jet streams south winter north summer

34. Wind and geopotential 200 hPa Note: Variability in east-west of the wind field. Note: Time variability of the wind field. Note: Troughs associated with mountain ranges, continents

35. Waves in the atmosphere • 300 mb Jet Stream Animation

36. Short summary • We have strong mean zonal winds. • We have latitudinal and time variability of the zonal winds • Quasi-stationary long waves. • On these quasi-stationary long waves, mid-latitude cyclones form and propagate.

37. Mid-latitude cyclones • What we know: • Low pressure systems • Form through spinup of low-level positive vorticity • Divergence/convergence is key • This is just the beginning… • Always closely associated with fronts—why? • Sometimes develop rapidly, sometimes not at all—why?

38. The mid-latitude cyclone

39. Mid-latitude cyclones: Norwegian Cyclone Model

40. Fronts and Precipitation Norwegian Cyclone Model CloudSat Radar

41. Relationship between upper troposphere and surface note tilt with height

42. Idealized vertical cross section

43. What’s at work here?

44. Mid-latitude cyclone development

45. Mid-latitude cyclones: Norwegian Cyclone Model • http://www.srh.weather.gov/jetstream/synoptic/cyclone.htm

46. warm Cold and warm advection cold

47. Lifting and sinking

48. Increasing the pressure gradient force

49. Relationship between upper troposphere and surface divergence over low enhances surface low // increases vorticity

50. Relationship between upper troposphere and surface vertical stretching // increases vorticity