Wind and Deserts Pressure The weight of the air above an object exerts a force upon that object, and this force is called pressure. Variations in pressure lead to the development of winds that play a significant role in shaping our daily weather. Winds flow from areas of high pressure to areas of low pressure - clockwise in the northern hemisphere Clouds A visible aggregate of tiny water (or ice) droplets suspended in the air Relative Humidity - 75% relative humidity means that the air contains three-quarters the amount of water vapor required for saturation. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. As air rises it tends to cool and water vapor may condense if saturation is reached Convective - hot air rises Convergence - two air masses meet and air column is forced upwards Orographic Interactions in the Atmosphere Reflection Scattering - Oxygen and Nitrogen scatter the shorter wavelengths - sky is blue Refraction Diffraction - light bends around an object If incoming solar radiation is 100 units: 16 units are absorbed by dust, water and ozone; 3 units are absorbed by clouds; 6 units are scattered back by air; 20 units are reflected by clouds; 4 units are reflected by the surface. 30 reflected back to atmosphere - the albedo - reflectivity : if the albedo decreased, the temperature goes up Earth receives 51 units These units heat up the Earth's surface and infrared radiation is emitted. The Earth's atmosphere absorbs some of this radiation. The greater the amount of absorbers (such as carbon dioxide), the greater the amount of heat absorbed and the higher the temperature. Thus, the Earth's atmosphere is relatively transparent to visible light but absorbs some of the outgoing infrared. Ozone (O3) absorbs ultraviolet - high energy Aeolian Sedimentation Modification of grain shape by the wind Accumulations Dune Fields Erosional Features The Rock Record