The lecture explains why wind blows and the factors affecting it.
Previous discussions included Earth's energy imbalance and winds' role in heat distribution.
Air Pressure and Wind Movement
Air Pressure: Highest at surface, varies by location.
Differences are temperature-induced due to varying sun angles.
Wind results from air pressure differences, moving from high to low pressure.
Key Terms
High Pressure Center: Location with relatively high air pressure; depicted with a blue 'H' on weather maps.
Low Pressure Center: Location with relatively low air pressure; depicted with a red 'L'.
Atmospheric Forces Influencing Winds
Pressure Gradient Force (PGF): Drives air molecules from high to low pressure areas - is the atmosphere's way of balancing out the pressure field, which causes wind to blow, always from high to low pressure.
**Coriolis Effect **: Apparent deflection of moving objects due to Earth's rotation. We are observing from a rotating reference frame since we are on a rotating earth.
Pressure Gradient Force (PGF)
Illustrated using a water beaker analogy; water flows from higher to lower level when separated by a divider.
Similarly, the atmosphere balances pressure differences, causing wind.
Coriolis Effect
Definition: Apparent deflection due to Earth's rotation.
Example: Merry-go-round analogy to demonstrate perceived curvature in motion.
Impact:
Increases with latitude and wind speed.
Zero at the equator.
Acts 90 degrees to the right of wind in the Northern Hemisphere and to the left in the Southern Hemisphere.
Global Wind Patterns
Pressure Variation: Shown from equator to poles, affecting wind direction.
Three Circulation Cells:
Hadley Cell: Equator to 30° N
Ferrel Cell: 30° N to 60° N
Polar Cell: 60° N to the North Pole
Wind Direction:
Equator: East to west (easterly trade winds).
45° N: West to east (westerly winds). coriolis effect is always at a 0 (equator) degree deviation
Vertical Circulation
Low pressure at equator leads to rising air; high pressure at 30° N leads to sinking air.
Climate and Air Pressure
High Pressure Areas: Clear, dry weather.
Low Pressure Areas: Cloudy, rainy weather.
Impact on Climate:
Rainforests near equator due to low pressure.
Deserts around 30° latitude due to high pressure.
Mid-latitude cyclones at 60° latitude.
Polar high pressure leads to cold, clear conditions.
Global Precipitation Patterns
Rain follows low pressure; most precipitation at the equator and 60° N.
Visual map of global precipitation aligns with pressure zones.
Practice Problems
Exercises to reinforce understanding of circulation cells, pressure forces, and real atmospheric wind directions.
Summary
Through understanding pressure centers and atmospheric forces, wind patterns and their climatic effects can be predicted.
Importance of air pressure in determining regional climates and weather patterns.