Page 168 - Handbook of Gold Exploration and Evaluation
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146    Handbook of gold exploration and evaluation































                     3.6 Magnetopause and magnetosphere, Van Allen Belt in black on either side
                     of the Earth (after Strahler and Strahler, 1992).


              corkscrew fashion along the lines of force suddenly increasing the magnetic
              field strength many fold. An ensuing magnetic storm simultaneously generates
              electrical currents in a layer of ionised atmospheric gases (the ionosphere) that
              sets in at about 50 km from the surface and extends to an altitude of 1000 km.
              Voltage fluctuations may reach 1,000 to 2,500 volts during violent storms.
              Dynamic currents measured in thousands of amperes flow in enormous
              horizontal circular patterns around the Earth giving rise to a series of electrical
              currents in a shallow layer of the Earth's surface. Technologies that rely upon
              electronics are affected by magnetic storms in two different ways. Circulating
              electrical currents disrupt radio communications, which depend upon the
              reflection of radio waves in the ionosphere; and television systems, which affect
              the functioning of navigation satellites on which modern global positioning
              systems rely (refer to Chapter 5). Induced electrical currents in high-tension
              power transmission lines at ground level overheat transformers and cause major
              shutdowns.


              Insolation

              The amount of direct and diffuse solar radiation reaching a unit horizontal area
              of the Earth is defined as insolation. A heat surplus in the low latitudes, between
              about 37ë N and 37ë S of the equator, is reversed in the high latitudes where out-
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