Wind: Global Systems Chapter 7

Overview of Global Circulation and Jet Streams

  • Global Circulations: The atmosphere consists of three main cells — Hadley Cell (0° latitude), Ferrell Cell (between 30° and 60° latitude), and Polar Cell (60° latitude to poles). These cells influence jet streams and surface winds directionally.

  • Relation to Jet Streams: The subtropical jet stream and the polar jet stream are influenced by the interactions of these three cells, affecting weather patterns and systems.

Thermal Circulations

  • Monsoons: Seasonal winds that create wet and dry periods.

  • Mountain and Valley Breeze: Updrafts during the day as surfaces heat (valley breeze) and downdrafts at night as cooling occurs (mountain breeze).

  • Sea Breeze: Wind going from sea to land due to temperature differences.

  • Santa Ana Wind: A warm, dry wind in Southern California, impacting wildfire conditions.

  • Haboob: Intense dust storms that occur in arid regions.

ENSO (El Niño Southern Oscillation)

  • Impact on Texas: Influences rainfall patterns, leading to wetter or drier conditions.

Upwelling and Downwelling Circulation

  • Upwelling: Nutrient-rich waters rise, supporting marine life.

  • Downwelling: Cold, dense water sinks, impacting ocean health.

Air Masses and Fronts

  • Basic Air Masses: Characterized by temperature and humidity - Polar (P), Tropical (T), Arctic (A), Maritime (m), and Continental (c).

  • Source Regions: Ideal for air mass formation include consistent conditions (e.g., tranquil areas).

  • Weather Impact: Maritime polar (mP) and continental tropical (cT) air masses affect US weather; mP brings moisture; cT brings heat.

  • Movement: Generally moving from high to low-pressure areas, often from the west in the U.S.

Synoptic Scale vs. Mesoscale

  • Differences: Synoptic scale covers larger systems like cyclones, while mesoscale involves smaller systems like thunderstorms.

  • Fronts: Understanding various types - cold, warm, occluded, and stationary. Each leads to different weather patterns:

  - Occluded Fronts: Bring complex weather as cold air overtakes warm air.
  - Dryline: Distinction of moisture content, crucial for thunderstorm development.

Mid-Latitude Cyclones and Cyclogenesis

  • Upper Levels: Features divergence aiding in cyclone formation, influenced by jet streams.

Thunderstorms

  • Ingredients: Moisture, instability, and lift are essential for formation.

  • Severe Thunderstorm Criteria: Features such as organized structure and potential for hail/wind.

  • Supercells: Long-lasting thunderstorms powered by persistent updrafts and a rotating structure.

  • Squall Lines: Formed along cold fronts, associated with severe weather.

  • Thunderstorm Dissipation: Occurs if updrafts weaken, or precipitation drags air down, causing downdrafts.

  • Structure of a Supercell: Includes updraft, downdraft, and mesocyclone.

Updrafts and Downdrafts

  • Causes: Updrafts result from heating and instability; downdrafts occur when precipitation drags air down.

  • Doppler Radar: Essential for monitoring storms and detecting wind patterns.

Thunder & Lightning

  • Charge Separation: Occurs in clouds, with negative charges concentrated at the base and positive charges at the top.

  • Lightning Types: Includes cloud-to-ground, in-cloud, etc., and involves rapid discharge of electricity.