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LIFE CYCLE OF EXTRA-TROPICAL CYCLONE

Understand the stages of a mid-latitude cyclone, from initial development to dissipation, with a focus on cloud patterns and frontal interactions. Learn how these systems evolve and impact weather patterns.

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LIFE CYCLE OF EXTRA-TROPICAL CYCLONE

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  1. LIFE CYCLE OF EXTRA-TROPICAL CYCLONE

  2. Initially there is a boundary or front, separating warm air to the south from cold air to the north The front is often stationary Life Cycle of Mid-latitude Cyclone

  3. Life Cycle of Mid-latitude Cyclone • An upper level disturbance embedded in the jet stream moves over the front • A wave forms on the front • The front develops a "kink" where the wave is developing

  4. Life Cycle of Mid-latitude Cyclone • Precipitation commences and it is heaviest along the front (dark green)

  5. Life Cycle of Mid-latitude Cyclone • As the wave intensifies, both cold and warm fronts become better organized

  6. Life Cycle of Mid-latitude Cyclone • The wave becomes a mature low pressure system, while the cold front, moving faster than the warm front, "catches up" with the warm front • As the cold front overtakes the warm front, an occluded front forms

  7. Life Cycle of Mid-latitude Cyclone • As the cold front continues advancing on the warm front, the occlusion increases and eventually cuts off the supply of warm moist air, causing the low pressure system to gradually dissipate

  8. Winds • Southerly winds east of the low transport warm and moist air northward and this moisture often contributes to the development of precipitation • A warm front marks the leading edge of this warm, moist air mass • Behind the low, northerly winds transport colder and drier air southward, with a cold front marking the leading edge of this colder, drier air mass

  9. Satellite Imagery • On satellite images, a mature mid-latitude cyclone is easily identifiable by a comma-shaped cloud • Satellite images show four stages of development of an mid-latitude cyclone

  10. Leaf Stage • During the initial development of a mid-latitude cyclone, the cloud pattern appears in the shape of a leaf • This characteristic shape is often observed on the east side of an upper-level trough

  11. Leaf Stage • The leaf shaped pattern is caused by the jet stream pushing into the western edge of the cloud system and spreading the cloud down wind

  12. Leaf Stage • The highest cloud tops are over the eastern portion of the leaf • Middle-level clouds are over the westward portion • The leaf cloud is a significant region of clouds and precipitation, even if cyclogenesis does not occur • The western edge of the leaf has a well-defined border

  13. Open Comma Stage • A comma shaped cloud pattern appears in satellite images when the mid-latitude cyclone has well-developed warm and cold fronts • As the comma cloud pattern develops, pressure at the surface usually falls

  14. Open Comma Stage • The back edge of the common cloud pattern is easily identified and represents the position of the cold front and the clouds, often thunderstorms, form because of the frontal lifting • The front edge of the comma cloud pattern is more diffuse as upper-level winds make the clouds to spread out

  15. Occluded Stage • As the occlusion forms, the low-pressure circulation separates from the jet stream • This is the mature stage of the storm, when the central pressure in the storm stops falling • The point at which the occluded, cold and warm fronts come together is referred to as the triple point, and it is often seen in satellite imagery where the jet stream cuts across the system

  16. Occluded Stage • The cloud pattern is still in the shape of a comma, the clouds spiral around the centre of the storm located in the head of the comma

  17. Occluded Stage • The cloud pattern is still in the shape of a comma, the clouds spiral around the centre of the storm located in the head of the comma

  18. Dissipating Stage • As the storm system continues to weaken, upper-level winds tend to tear it apart and the system becomes disorganised

  19. Dissipating Stage • The cloud system loses its organisational pattern and the comma head gets cut off from the tail

  20. Dissipating Stage • The comma head and its associated low pressure may lag behind and continue to rotate • Such cut-off, cold-core lows weaken slowly with time and tend to be very persistent

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