Chapter 8: Air Masses, Fronts, and Cyclones Notes

Chapter 8: Air Masses, Fronts, and Cyclones

Section A: Extratropical Cyclones

Extratropical Cyclones (frontal cyclones, wave cyclones)

  • Large low-pressure systems outside the tropics, move west to east.

  • Gain energy from temperature differences across the polar front.

  • Also called frontal cyclones or wave cyclones, last a few days to a week.

  • Identifiable on daily weather charts.

Airmasses

  • Large, uniform bodies of air; classified by source region (Arctic, Polar, Tropical) and temperature (continental or maritime).

  • Modify as they move; e.g., cP air becomes mP over oceans.

Fronts

  • Boundaries between different airmasses.

  • Types: cold (advancing cold air), warm (advancing warm air), stationary, occluded.

  • Fronts cause clouds and precipitation due to lifting of moist air.

  • Frontal zones are narrow, with wind shear and turbulence.

Extratropical Cyclone Development

  • Develop along large temperature gradients (polar front).

  • Cyclogenesis common where cold continents meet warm oceans (e.g., Gulf of Mexico).

  • Cyclone structure: wave cyclone → occlusion → dissipation.

Wind Shear & Cyclone Stages

  • Wind shear: change in wind speed/direction.

  • Stages: Wave cyclone → occlusion → dissipation.

Cyclone Structure Aloft

  • Upper-level troughs develop before surface cyclones.

  • Jet stream intensifies with cyclone development, affecting cloud patterns.

Cyclone Behavior & Variations

  • Models help with predictions, but occluded cyclones can vary due to geographical features.

Section B: Tropical Cyclones and Hurricanes

Tropical Cyclones (Hurricanes)

  • Form in tropical easterlies, develop over warm water (27°C/80°F).

  • Stages: tropical depression → tropical storm → hurricane (≥64 knots).

  • Names vary (e.g., Typhoons in the Western Pacific).

  • Impact: storm surge, winds, tornadoes.

Development & Behavior

  • Form within 1,200 nm of equator, move west/northwest.

  • Weaken over land/cold water or transform into extratropical cyclones.

Structure & Weather

  • Eye (calm), eye wall (strong winds), spiral rainbands (thunderstorms).

  • Strongest winds and worst weather in right front quadrant (Northern Hemisphere).

Flight Hazards & Warnings

  • Flight near hurricanes: strong winds, thunderstorms, heavy rain.

  • National Weather Service issues watches (days ahead) and warnings (24 hours ahead).