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Meteorology
3.4.3 The Earth's surface and the geostrophic wind
Winds arise as a result of temperature differences and the consequent pressure
differences, which cause a gradient force (pressure change per unit distance).
Wind direction is determined by:
- The Coriolis force
- The location of pressure systems
Wind speed is determined by:
- The gradient force (isobar distance hPa / distance in km)
- Friction (with the Earth's surface)
Winds are divided into:
- Geostrophic winds (above 2000 feet)
- Winds in the friction layer (surface winds 0-2000 feet)
3.4.3.1 The Geostrophic Wind
The geostrophic wind is located above the friction layer (the layer in which wind
speed is reduced due to friction with the Earth).
In the Northern Hemisphere, low pressure will be to the left, and high pressure
will be to the right, relative to the geostrophic wind's direction.
When air moves from high pressure to low pressure, it will be affected by the
Coriolis force.
The wind direction will be:
- High pressure: to the right
- Low pressure: to
the left
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 253
