WindThe winds are major influences in our weather patterns, the production of ocean waves, and as the major formative influences in desert regions. Winds result from any influence that creates differences in atmospheric pressure. On Earth, global wind patterns are influenced by several factors: First, the planet's rotation creates counterclockwise low pressure cell rotations in the Northern hemisphere and corresponding clockwise rotation in the Southern hemisphere (the coriolis effect). Second, the warming influence of ocean currents and atmospheric capture of solar heat. Third, convection cells (Hadley cells) create low pressure gradients in regions such as the equator, high pressures at 30 degrees north and south (areas with major deserts), and low pressure zones at 60 degrees north (the maritimes), and finally, another high pressure area at the poles. Examples of globally-influenced winds are the 'Trade Winds' in the tropics and the 'Roaring Forties' with extremely dry conditions in subpolar regions. Heated air, driven upward by solar convection, will then cool rapidly as it rises and attempt to maintain angular momentum, rushing downward seeking areas of low pressure again. However, these air currents are deflected perpendicular to their velocity by coriolis acceleration. In an attempt to reach equilibrium between its linear velocity and normal coriolis forces, winds will then begin to curl in the direction of angular rotation and form circular low-pressure cells, known as cyclones or hurricanes. Subject to coriolis forces, a particle will begin to rotate with velocity v and a rotational frequency f which gives R = v / f for the radius of the cyclone cell. - Climatologists recognize convection cells and cyclone formation as a major route for temperature equilibrium on the planet, redistributing vast amounts of atmospheric thermal energy worldwide. The coriolis effect is also thought to influence ocean waves through the Ekman offset, as well as Rossby and Kelvin waves in the troposphere. Regionally, winds can be created by adiabatic processes as moisture-laden winds travelling over bodies of water reach land, and by regional evaporation and precipitation of moisture, leading to dramatic seasonal wet-dry cycles such as the monsoons in India and SE asia. It is thought that adiabatic winds resulting from temperature gradients in glacially active regions helped create eolian loess deposits in areas such as Inner Mongolia, the Midwest US, and Northern Europe.Ablation and transport of soil particles will occur in areas of high winds, with deposition occuring in areas of decreasing energy gradients. Though eolian processes do not account for the deposition volumes of fluvial or marine processes worldwide, wind is an important means of mass transport in desert regions today, and fossil loess deposits of windblown silt can reach a hundred meters or more in thickness, yielding rich but fragile farmland in these areas. | Index Geophysics concepts Reference Lutgens & Tarbuck Ch 12 | ||
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