1. MID LATITUDE CYCLONE
Fg Offr Seljin Mathew

2. Introduction
A cyclone is an area of low pressure around which the winds flow counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere
However, the characteristics of mid-latitude cyclones are significantly different from those of a tropical cyclone

3. MID LATITUDE CYCLONE
A developing cyclone is typically accompanied by a warm front pushing northward and a cold front pulling southward, marking the leading edges of air masses being wrapped around a centre of low pressure, or the centre of the cyclone

4. MID LATITUDE CYCLONE
The counter clockwise winds associated with northern hemisphere mid-latitude cyclones play a significant role in the movement of air masses
They transport warm moist air northward ahead of a low while dragging
colder, drier air southward
behind it

5. MID LATITUDE CYCLONE
Rising air in the vicinity of a low pressure centre favours the development of clouds and precipitation, which is why cloudy weather (and likely precipitation) are commonly associated with an area of low pressure
In satellite images, cyclones are identifiable by the characteristic comma shaped configuration of cloud bands

6. LIFE CYCLE OF A MID LATITUDE CYCLONE
Initially there is a boundary or front, separating warm air to the south from cold air to the north
The front is often stationary

7. LIFE CYCLE OF A 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

8. LIFE CYCLE OF A MID LATITUDE CYCLONE
Precipitation commences and it is heaviest along the front (dark green)

9. LIFE CYCLE OF A MID LATITUDE CYCLONE
As the wave intensifies, both cold and warm fronts become better organized

10. LIFE CYCLE OF A 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

11. LIFE CYCLE OF A 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. OPEN COMMA STAGE 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

18. 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

19. 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

20. 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

21. DISSIPATING STAGE
As the storm system continues to weaken, upper-level winds tend to tear it apart and the system becomes disorganised

22. DISSIPATING STAGE
The cloud system loses its organisational pattern and the comma head gets cut off from the tail

23. 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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