Chapter 6: Understanding Air Pressure and Winds

Key Concepts

• Wind Creation: Wind is created by differences in air pressure (pressure gradient force).
• Flow Direction: Wind flows from areas of high pressure to areas of low pressure.
• Forces Influencing Wind:
  • Pressure Gradient Force: Drives wind from high to low pressure.
  • Coriolis Force: Deflects wind to the right in the Northern Hemisphere due to Earth's rotation.
  • Friction: Slows down wind and alters its direction at the surface.

Air Pressure Basics

• Definition: Pressure exerted by the weight of the air.
• Measurement:
  • Standard sea level pressure is 1013.25 millibars.
  • Pressure is measured using barometers (digital or analog).

Isobars

• Definition: Lines on a weather map representing areas of equal air pressure.
• Significance: Indicate regions of high and low pressure.
  • Close isobars = steep pressure gradient = stronger winds.

Factors Affecting Air Pressure

• Temperature: Colder air masses exert higher pressure.
• Humidity: Dry air masses exert higher pressure.
• Seasonal Variations: Higher surface pressure in winter, lower in summer.

Wind Dynamics

• Surface Winds:

  • Influenced by pressure gradient, Coriolis force, and friction.
  • High Pressure (Anticyclones): Clockwise wind flow.
  • Low Pressure (Cyclones): Counterclockwise wind flow.

• Upper-Level Winds:

  • Less affected by friction, flow parallel to isobars.
  • Geostrophic Wind: Resultant wind flow above ground level.

Weather Systems

• Cyclones: Low pressure, counterclockwise flow, associated with clouds and precipitation.
• Anticyclones: High pressure, clockwise flow, generally clear weather.

Wind Measurement

• Tools:
  • Wind Vane: Measures wind direction.
  • Cup Anemometer: Measures wind speed.
  • Wind Sock: Provides visual wind direction and speed, commonly used at airports.
  • Aerovane: Measures both speed and direction.
  • Doppler Radar: Estimates wind speed and direction.

Practical Applications

• Weather Maps:
  • Identify types of winds and pressure systems using isobars, wind barbs, and pressure gradients.
  • Pressure Tendency: Indicates potential weather changes based on rising or falling pressure.

Conclusion

• Summary: Understanding the forces and factors influencing wind and air pressure helps predict weather patterns and conditions.
• Further Study: Review chapter notes and class materials. Contact instructor for clarification or questions.

Note: This chapter introduces fundamental concepts that will be further explored in subsequent chapters, particularly in relation to weather systems and forecasting.