Wind - Chapter 2 notes

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Environmental Science
Tanzina Mohsin

EESA09 Lecture 2 What is Wind? Differences in air pressure (Vertical or horizontal) produce a pressure gradient Pressure Gradient Force In the absence of other forces, air moves from high pressure to low pressure Steep PG (closely spaced isobars) indicate strong PGF Coriolis Force Because the earth rotates, the rotation directly results in a fictitious force called Coriolis Force Gustave de Coriolis (1835) Northern Hemisphere Deflects wind to the right Southern Hemisphere Deflects wind to the left Above the surface of earth (1 km or more), when there is a balance between pressure gradient force and the Coriolis force, geostrophic wind is formed The only way to achieve a balance between these forces is for the wind to flow perpendicular to the pressure gradient Below 1 km, wind is influenced by friction (three way balance) Wind flows towards centre of a low and away from the high pressure centre Global Circulation Air has natural inclination to move from high pressure to low pressure, but is modified by: a) Earth rotation creating the Coriolis effect causes wind to deflect (NH=R, SH=L) b) Earth surface contributes friction which slows down and redirects (funnels) the wind c) LandSea contrast leading to temperature differences between land and water surface also influences the wind (continentality) d) Wind vary with season (caused by tilt of earth)
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