Geostrophic Winds
Earth's atmosphere is very thin in comparison to its diameter of 12,000 km. The troposphere, which extends to about 11 km altitude, is where all of our weather, and the greenhouse effect occurs. As a comparison, if the globe were a ball with a diameter of 1.2 metres, the atmosphere would only be 1 mm thick.
The Geostrophic Wind
Geostrophic winds are those which act on a global scale. The geostrophic winds are largely driven by temperature differences, and thus pressure differences, and are not influenced by the relief of the surface of the earth. Geostrophic winds are found at altitudes of 1000 metres and above. Geostrophic wind speed can be measured using weather balloons.
Surface Winds
Below 100m of altitude, winds are very much influenced by the ground surface. The wind will be slowed down by the Earth's surface roughness and obstacles. Wind directions near the surface will be slightly different from the direction of the geostrophic wind because of the Coriolis Force.