Lecture Notes: Mid-Latitude Cyclones

Introduction

• Speaker: Ana
• Topic: Mid-Latitude Cyclones
• Context: South African weather phenomenon occurring mainly in winter, particularly affecting South Africa.

Overview of Mid-Latitude Cyclones

• Definition:
  • Low-pressure weather condition
  • Occurs in winter between 30° to 60° latitudes
  • Moves eastwards (from west to east)
• Characteristics of Low Pressure:
  • Associated with rising air
  • Northern Hemisphere: Air rises anticlockwise (counterclockwise)
  • Southern Hemisphere: Air rises clockwise

Occurrence

• Season: Winter
• Location: Between 30° to 60° latitudes (mid-latitude region)
• Movement: Eastwards due to westerly winds

Formation Stages of Mid-Latitude Cyclones

1. Initial Stage

• Latitude Line: 60° latitude, called the Polar Front
• Wind Movements:
  • Polar Easterlies: Move from east to west
  • Tropical Westerlies: Move from west to east
• Interactions: Polar Easterlies move north, forcing Tropical Westerlies south, but do not mix.

2. Wave Formation Stage

• Air Movements:
  • Polar Easterlies uplift warm air, causing a low-pressure area
• Formation: Leads to a wave pattern where warm air rises sharply

3. Mature Stage (Most Important)

• Diagram: Important to draw cross-section diagrams
• Fronts:
  • Warm Front: Warm air sector
  • Cold Front: Cold air sector
• Weather Map Representation:
  • Cold Front: Depicted with spikes
  • Warm Front: Smooth line
• Weather Conditions:
  • Warm Sector: Light, warm air
  • Cold Front: Heavy, dense air causing uplift and formation of cumulus clouds
  • Heavy precipitation occurs behind the warm front, light precipitation in front
• Movement: Cyclone moves on a circular path
  • Southern Hemisphere: Clockwise
  • Northern Hemisphere: Counterclockwise

4. Occluded Stage

• Description: Cold front catches up with the warm front, leading to uplift
• Outcome: Mixing of cold and warm air masses

5. Dissipating Stage

• Final Stage: Cold front fully mixes with warm front
• Result: Cyclone dissipates

Conclusion

• Key Points:
  • Understand each stage for full understanding and exam success
  • Engage with content through drawing and reviewing videos
• Next Topic: Transition to Tropical Cyclones

• Action Items:
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