Lecture on Wind Dynamics

Overview

• Pressure influences global circulation, wind velocity, and wind direction.
• Key elements: Pressure Gradient Force, friction, and Coriolis Force.

Pressure and Wind Dynamics

• Pressure Gradient Force:
  • Air flows from high to low pressure.
  • High pressure systems direct low pressure systems.
  • Temperature and density variations influence pressure differences and wind.
• High vs Low Pressure Systems:
  • Cold, dry air sinks (high pressure), warm, wet air rises (low pressure).
  • Low-density air rises, high density sinks.
• Practical Example:
  • Open a fridge or top-loading freezer to feel cold air sinking.
• Wind Velocity Influences: Three Main Forces:
  1. Pressure Gradient Force.
  2. Friction.
  3. Coriolis Force.

Detailed Forces Influencing Wind

• Pressure Gradient Force (ΔP/S):
  • Change in pressure over a distance.
  • Example: 1,20 mbars to 1,0 mbars over 100 km (0.1 mbars/km).
  • Larger pressure differences yield higher wind velocities.
  • Example: Tropical storm with a 40 mbar change over 100 km (0.4 mbars/km).
• Friction:
  • Slows wind velocity, more pronounced with obstacles (e.g., trees).
  • Less friction over plains/open fields, more in forests.
  • Higher elevation/altitude yields less friction.
• Coriolis Force:
  • Deflects objects to the right in the Northern Hemisphere, left in Southern Hemisphere.
  • Influences wind patterns and directions.
  • Does not exist at the equator due to rotational speed.
  • Stronger away from equator.
  • Important for hurricane formation (5° to 20° latitude).

Practical Applications and Examples

• Isobars:
  • Lines of equal pressure.
  • Close isobars = stronger pressure gradient force, higher winds.
  • Wide isobars = weaker pressure gradient force, calmer winds.
  • Must adjust for elevation.
• Influence of Terrain:
  • Unadjusted pressure charts can be misleading due to topography.
  • Adjusting for sea-level gives accurate atmospheric pressure readings.
• Maritime Impacts:
  • Little friction over oceans, leading to higher wind energy transfer and larger waves.
  • Example: Southern Pacific storm with 36-foot wave heights.
• Cyclones and Anticyclones:
  • Northern Hemisphere: Low pressure systems (counterclockwise rotation), High pressure systems (clockwise rotation).
  • Southern Hemisphere: Opposite rotational directions.
  • High pressure = clear and dry, low pressure = clouds and precipitation.

Upper-Level Wind Dynamics

• Upper-level winds experience low friction.
• Coriolis Force causes winds to flow parallel to isobars at higher altitudes.

Upcoming Topics:

• Future lectures will cover wind patterns and names of different wind belts.