mid latitude cyclone notes

Introduction to Mid Latitude Cyclones

  • There are five important stages in the formation of mid latitude cyclones.
  • Discussion includes characteristics, necessary conditions for formation, stages, effects, and precautionary strategies.
  • Importance of these topics as they often appear as essay questions worth about eight marks each.

General Characteristics of Mid Latitude Cyclones

  • Also known as temperate or extra tropical cyclones.
  • Definition: Large weather systems occurring between 30° and 60° latitude in both hemispheres.
  • Remember: "Mid latitude cyclones" and "temperate cyclones" refer to the same systems.

Movement

  • Direction of movement: West to East (easterly direction).
  • Question: In which direction do mid latitude cyclones move? Answer: West to East.

Size and Duration

  • Diameter: Approximately 1,000 kilometers.
  • Weather conditions associated:
    • Varied weather including cloud cover, strong winds, and precipitation.
  • Affect South Africa mainly in winter.
  • Duration: Generally lasts between 4 to 14 days.

Conditions Necessary for Formation

Meeting of Air Masses

  • Warm subtropical air from 30° N/S meets cold polar air from 90° N/S at the Polar Front (located at 60° N/S).
    • Polar Front (60° N/S) is vital for formation of cyclones.
  • Diagram explanation:
    • Warm air from 30° N moves north while cold polar air from 90° N moves south (and vice versa in the Southern Hemisphere).

Air Mass Movement and Frictional Drag

  • Both air masses move parallel to each other in opposite directions.
  • Three reasons for frictional drag between the air masses:
    1. Difference in speed:
    • Cold air is denser and moves quicker than warm air.
    1. Uneven surface effects: Interaction with different terrains.
    2. Temperature differences between land and sea surfaces.

Stages in Formation of Mid Latitude Cyclones

Stage 1: Initial Stage

  • Warm, moist subtropical air meets cold, drier air along a stationary polar front.
    • Polar front can also be referred to as a stationary front.
  • Diagram indicates warm subtropical air (red arrow) and cold polar air (blue arrow).
  • Air masses move parallel to each other at the polar front.

Stage 2: Wave Stage

  • Characteristics:
    • Cold front and warm front form a wave shape.
  • Identification: Warm front with semicircles; cold front with triangles.
  • Process of warm air uplifted by cold air: Cold air is denser and moves faster.
  • Development of low-pressure center at the point of contact of the air masses.

Stage 3: Mature Stage

  • Cyclone intensifies, forming a distinct V shape in the diagram.
  • Pressure readings:
    • Center pressure: 1,002 millibars.
    • Outward pressure rises to 1,004 millibars.
  • Distinct cold and warm fronts; organized open wave shape.
  • Associated weather conditions: Widespread cloud cover, precipitation, and strong winds.
  • Variations in weather patterns on either side of fronts due to different front types.

Stage 4: Occlusion Stage

  • Characteristics:
    • Cold front catches up to warm front resulting in an occluded front.
  • Lowest pressure observed in the center (998 millibars).
  • Process of occlusion:
    • Cold front's density causes it to move quicker, lifting warm air off the ground.
  • Impact: Weather system begins to weaken; heavy precipitation is possible as warm, moist air rises rapidly.

Stage 5: Dissipation Stage

  • Occurs when the energy source (temperature contrast) begins to weaken.
  • Warm air is fully lifted and cyclone loses strength.
  • Weather conditions improve with fewer clouds and reduced precipitation.

Impacts of Mid Latitude Cyclones

Positive Impacts

  • Mid latitude cyclones bring rain and snow essential for ecosystems, agriculture, and human use.
  • Critical for replenishing soil and water reserves, especially in dry areas.
  • Rain carries nutrients into the soil promoting healthy crops and vegetation.
  • Strong winds can help clear pollutants from the atmosphere, improving urban air quality.
  • Contribution to snowpack accumulation leading to vital water sources during warmer months.

Negative Impacts

  • Heavy rainfall can lead to flash flooding or river floods, notably in low-lying areas.
    • Structural damages to homes, roads, farmland and the potential for loss of life.
  • Prolonged storms can devastate crops and livestock through various severe weather conditions.
  • Soil erosion from heavy rains, resulting in environmental damage.
  • Rough seas and hazardous marine conditions disrupting global shipping and safety of maritime operations.

Precautionary and Management Strategies

Strategies to Mitigate Impact

  1. Avoid building houses in low-lying areas prone to flooding.
  2. Implement efficient drainage systems in urban areas to alleviate flooding risks.
  3. Utilize shelters for livestock (e.g., sheds, barns) to protect them during storms.
  4. Maintain adequate food supplies for livestock to prevent losses during severe weather.
  5. Monitor weather patterns consistently, especially before outdoor activities (even simple trips).
  6. Stay indoors during hazardous weather conditions; heed storm warnings.
  7. Stockpile essentials like food, batteries, and medication in preparation for severe weather.
  8. Construct and maintain sea walls, levees, and storm surge barriers to protect coastal areas.
  9. Identify and zone high-risk flood areas to prevent construction and minimize damage from flooding.

Conclusion

  • Emphasis on thorough preparation and understanding of mid latitude cyclones due to their significant impacts and recurrent appearance in exam scenarios.
  • Encouragement of proactive studying and strategy review for optimal exam performance.