Mid-latitude cyclones

• Other names:

  Frontal Depression

  Temperate

  Extra Tropical
• Mid-latitude cyclones occur at 40 degrees to 60 degrees North & South
• Warm Front

  • The air behind the warm front is warm
  • The air in front of the warm front is cold
• Cold Front

  • The air behind the cold front is cold
  • The air in front of the cold front is warm
• These cyclones move eastward over land and are often associated with extreme winter weather such as wind, snow, and ice.
• Ocean currents play an important role in mid-latitude cyclone formation by providing energy and moisture to fuel storm development.
• Wind roration always clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere
• We have a low pressure system because the air is rising and the air is cooler than the air above it
• A high pressure system has sinking air which means that the air is warmer than the air below it
• High pressure systems are usually dry and sunny while low pressure systems can be cloudy and wet
• Mid-latitude cyclones move from west to east because it is carried by the Tropical Westerlies
• Stages of development

  1. Initial Stage
  2. Developing Stage
  3. Mature Stage
  4. Degeneration stage (Dissipating)
• In the Initial Stage cold air from the polar easterlies meets with warm air from the westerlies at the polar front (60 degrees)
• In the Developing Stage wave movements develop along the polar front. The regular surface becomes disturbed and a vortex of low press develops at the apex. The air circulation converges in a direction in the Southern Hemisphere around the LP
• In the Mature Stage

  • A clear low pressure centre has formed with a distinct cold front and warm front.

  • Behind the warm front, the mass of warm air turns towards the poles and forms the warm sector:

  • Behind the cold front the cold air mass turns towards the equator and forms the cold sector.

  • The entire mid-latitude cyclone moves eastwards.
• In the Occluded stage

  • While the mid-latitude cyclone is moving eastwards the cold front catches up with the warm front (cold air is more dense and therefore travels faster).
  • The cold air then pushes the warm air from the warm sector up and out of the cyclone until the cold front merges with the warm front and they form an occluded front.
• In the Degeneration stage

  • Eventually the low pressure centre is surrounded entirely by cold air and the weather system dissipates.
• Cold Front Occlusion:

  Air behind the cold front is colder and therefore denser than the air ahead of the warm front.

  The cold front remains in contact with the ground, and lifts the warm front.

  
• Warm Front Occlusion:

  Air behind the cold front is warmer and therefore lighter than the air ahead of the warm front. The warm front remains in contact with the ground, and the cold front rises.