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Midlatitude Weather Systems ATMS 490

Learn about the jet stream, a narrow current of strong winds in the midlatitude tropopause. Discover its characteristics, effects on weather, and its association with temperature gradients and air masses.

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Midlatitude Weather Systems ATMS 490

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  1. Midlatitude Weather SystemsATMS 490

  2. The Large Scale Picture

  3. Jet Stream A jet stream (or jet) is a narrow current of strong winds. Can exist at several levels, but most often applied to the high velocity winds in the vicinity of the midlatitude tropopause

  4. Midlatitude Jet Stream Facts • Can reach 250 mph (or more) • Centered on the upper troposphere…around 250 hPa (30,000 ft) • Stronger in winter. Generally, weakens and moves northward during summer. • Closely associated with a tropospheric temperature gradient (thermal wind!) • Not uniform zonally

  5. Wasaburo Oishi, Japanese Discoverer (1920s)

  6. Fu-Go Balloon Weapon During WWII

  7. Strahlstromung (German) for “jet stream” first used in 1939 • Big effects on bomber flights during WWII

  8. B-29s flying westward to Japan

  9. Jet Stream winds are not uniform

  10. 250 mb isotach

  11. Jet Streams are NOT uniform

  12. Main Upper Tropospheric Jets Closely Associated with the Tropopause

  13. Tropopause

  14. http://itg1.meteor.wisc.edu/wxwise/AckermanKnox/chap7/subtropical_jet.htmlhttp://itg1.meteor.wisc.edu/wxwise/AckermanKnox/chap7/subtropical_jet.html

  15. Why are their jet streams?

  16. Thermal Wind Equation

  17. Or alternatively…

  18. The Jet Stream The Jet Stream results from temperature gradients 500 mb 700 mb 850 mb Psurface Warm Cold

  19. 250 mb isotach

  20. Lower atmosphere temperature gradient

  21. Air Masses

  22. Maritime Tropical (mT) Source Region

  23. Continental Polar (cP) Source Region

  24. Continental Tropical (cT) Source Region

  25. Maritime Polar (mP) Source Region

  26. Bering Sea Cloud Streets (cP to mP)

  27. Where air masses of differing temperatures come together, we see fronts

  28. Fronts An Important Midlatitude Weather Feature

  29. Definition You Should NEVER Forget A front is a boundary between relatively uniform warm air and a zone in which temperatures cools rapidly

  30. Four Main Types of Fronts

  31. Warm Front

  32. Stationary Fronts

  33. Occluded Front (a hybrid)

  34. As a front passes there are changes in: • Temperature • Dew point • Wind direction • Pressure • cloudiness

  35. Fronts and PressureFronts are associated with troughs of low pressure

  36. Fronts are associated with bands of clouds

  37. Vertical Structure of Fronts

  38. Cold Front • Slope ~1:50, moves fast (20-30 mph), convection on leading edge

  39. Warm Front • Smaller slope (~1:200), slower (1—15 knots), more stratiform clouds

  40. Stationary Front similar structure to warm front, but without movement

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