MID LATITUDE CYCLONE Fg Offr Seljin Mathew

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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